Patent Publication Number: US-11659169-B2

Title: Affine Linear Weighted Intra Predictions

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of copending International Application No. PCT/EP2019/074504, filed Sep. 13, 2019, which is incorporated herein by reference in its entirety, and additionally claims priority from European Application No. EP 18194357.2, filed Sep. 13, 2018, which is incorporated herein by reference in its entirety. 
     The present document relates to techniques including, inter alia, Affine Linear Weighted Intra Predictions (ALWIPs). 
    
    
     BACKGROUND OF THE INVENTION 
     Different inventive embodiments and aspects will be described. At least some of these embodiments refer, inter alia, to methods and/or apparatus for video coding, such as High Efficiency Video Coding (HEVC). 
     Also, further embodiments will be defined by the enclosed claims. 
     It should be noted that any embodiments as defined by the claims can be supplemented, in some cases optionally, by any of the details (features and functionalities) described in the following chapters. 
     Also, the embodiments described in the following chapters can be used individually, and can also be supplemented by any of the features in another chapter, or by any feature included in the claims. 
     Also, it should be noted that individual aspects described herein can be used individually or in combination. Thus, details can be added to each of said individual aspects without adding details to another one of said aspects. 
     It should also be noted that the present disclosure describes, explicitly or implicitly, features of decoding and/or encoding system and/or method. 
     Moreover, features and functionalities disclosed herein relating to a method can also be used in an apparatus. Furthermore, any features and functionalities disclosed herein with respect to an apparatus can also be used in a corresponding method. In other words, the methods disclosed herein can be supplemented by any of the features and functionalities described with respect to the apparatuses. 
     Also, any of the features and functionalities described herein can be implemented in hardware or in software, or using a combination of hardware and software, as will be described in the section “implementation alternatives”. 
     Moreover, any of the features described in parentheses (“( . . . )” or “[ . . . ]”) can be optional in some examples. 
     The achievement of more performing techniques for predicting blocks to be encoded and/or decoded is a constant goal of the technology. For example, it is advantageous to efficiently compress the datastreams to reduce the length of the code. 
     SUMMARY 
     One embodiment may have a decoder for decoding a picture from a data stream supporting a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction mode, configured to 
     decode a predetermined block of the picture by 
     
         
         
           
             assigning, based on a first signalization in the data stream, the predetermined block to the first set or the second set, 
             sorting the assigned set of intra-prediction modes according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block, to obtain a list of intra prediction modes, 
             deriving, for the predetermined block, from the data stream, an index into the list of intra prediction modes, 
             predicting the predetermined block using an intra prediction mode onto which the index points,
 
wherein decoder is configured to,
 
             if the assigned set is the first set of intra-prediction modes, in sorting the assigned set, use a second mapping which maps each intra-prediction mode of the second set of prediction modes onto a representative one in the first set of intra-prediction modes. 
           
         
       
    
     Another embodiment may have a decoder for decoding a picture from a data stream supporting, for each of different block sizes, a set of intra-prediction modes, configured to 
     decode a predetermined block of the picture by 
     
         
         
           
             sorting the set of intra-prediction modes for the block size of the predetermined block according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block, to obtain a list of intra prediction modes, 
             deriving, for the predetermined block, from the data stream, an index into the list of intra prediction modes, 
             predicting the predetermined block using an intra prediction mode onto which the index points,
 
wherein decoder is configured to,
 
             if one of the neighboring blocks is of a different size than the predetermined block, in sorting the assigned set, use a mapping which maps each intra-prediction mode of the set of prediction modes for the one neighboring block&#39;s block size onto a representative one in the set of intra-prediction modes for the predetermined block&#39;s block size. 
           
         
       
    
     According to an embodiment, a method for decoding a picture from a data stream supporting a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction mode, may have the steps of: 
     decoding a predetermined block of the picture by 
     
         
         
           
             assigning, based on a first signalization in the data stream, the predetermined block to the first set or the second set, 
             sorting the assigned set of prediction modes according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block to obtain a list of intra prediction modes, 
             deriving, for the predetermined block, from the data stream, an index into the list of intra prediction modes, 
             predicting the predetermined block using an intra prediction mode onto which the index points,
 
wherein decoding is based on,
 
             if the assigned set is the first set of intra-prediction modes, in sorting the assigned set, use a second mapping which maps each intra-prediction mode of the second set of prediction modes onto a representative one in the first set of intra-prediction modes. 
           
         
       
    
     According to another embodiment, a non-transitory digital storage medium may have a computer program stored thereon to perform the inventive method, when said computer program is run by a computer. 
     Another embodiment may have an encoder for encoding a picture on a data stream supporting a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction mode, configured to 
     encode a predetermined block of the picture by 
     
         
         
           
             assigning, and encoding on a first signalization in the data stream, the predetermined block to the first set or the second set, 
             sorting the assigned set of prediction modes according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block to obtain a list of intra prediction modes, 
             determining, for the predetermined block an index into the list of intra prediction modes, 
             predicting the predetermined block using an intra prediction mode onto which the index points,
 
wherein the encoder is configured to,
 
             if the assigned set is the first set of intra-prediction modes, in sorting the assigned set, use a second mapping which maps each intra-prediction mode of the second set of prediction modes onto a representative one in the first set of intra-prediction modes. 
           
         
       
    
     Yet another embodiment may have an encoder for encoding a picture onto a data stream supporting, for each of different block sizes, a set of intra-prediction modes, configured to 
     encode a predetermined block of the picture by 
     
         
         
           
             sorting the set of intra-prediction modes for the block size of the predetermined block according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block to obtain a list of intra prediction modes, 
             inserting, for the predetermined block, into the data stream, an index into the list of intra prediction modes, 
             predicting the predetermined block using an intra prediction mode onto which the index points,
 
wherein encoder is configured to,
 
             if one of the neighboring blocks is a different size than the predetermined block, in sorting the assigned set, use a mapping which maps each intra-prediction mode of the set of prediction modes for the one neighboring block&#39;s block size onto a representative one in the set of intra-prediction modes for the predetermined block&#39;s block size. 
           
         
       
    
     According to an embodiment, a method for encoding a picture on a data stream supporting a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction mode, may have the steps of:
         assigning, and encoding on a first signalization in the data stream, the predetermined block to the first set or the second set,   sorting the assigned set of prediction modes according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block to obtain a list of intra prediction modes,   determining, for the predetermined block an index into the list of intra prediction modes,   predicting the predetermined block using an intra prediction mode onto which the index points,   encoding the data stream,
 
wherein the encoder is configured to,
   if the assigned set is the first set of intra-prediction modes, in sorting the assigned set, use a second mapping which maps each intra-prediction mode of the second set of prediction modes onto a representative one in the first set of intra-prediction modes.       

     According to an embodiment, a non-transitory digital storage medium may have a computer program stored thereon to perform the inventive method, when said computer program is run by a computer. 
     According to another embodiment, a method for decoding a picture from a data stream may have the steps of:
         mapping a set of P neighboring samples neighboring the predetermined block using a linear or affine linear transformation onto a set of Q predicted values for samples of the predetermined block,   wherein the linear or affine linear transformation includes P*Q weighting factors among which at least ¼ P*Q weighting factors are non-zero weighting values, which include, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value, wherein the series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block, form an envelope which is omnidirectionally non-linear.       

     According to yet another embodiment, a non-transitory digital storage medium may have a computer program stored thereon to perform the inventive method, when said computer program is run by a computer. 
     Yet another embodiment may have an encoder for encoding a data stream from a picture, configured to
         map a set of P neighboring samples neighboring the predetermined block using a linear or affine linear transformation onto a set of Q predicted values for samples of the predetermined block,   wherein the linear or affine linear transformation includes P*Q weighting factors among which at least ¼ P*Q weighting factors are non-zero weighting values, which include, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value, wherein the series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block, form an envelope which is omnidirectionally non-linear.       

     According to yet another embodiment, a method may have the steps of:
         mapping a set of P neighboring samples neighboring the predetermined block using a linear or affine linear transformation onto a set of Q predicted values for samples of the predetermined block,   wherein the linear or affine linear transformation includes P*Q weighting factors among which at least ¼ P*Q weighting factors are non-zero weighting values, which include, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value, wherein the series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block, form an envelope which is omnidirectionally non-linear.       

     According to yet another embodiment, a non-transitory digital storage medium may have a computer program stored thereon to perform the inventive method, when said computer program is run by a computer. 
     In accordance to an aspect, there is a decoder disclosed for decoding a picture from a data stream, configured to predict a predetermined block of the picture by
         mapping a set of P neighboring samples neighboring the predetermined block using a linear or affine linear transformation onto a set of Q predicted values for samples of the predetermined block,   wherein the linear or affine linear transformation comprises P*Q weighting factors among which at least ¼ P*Q weighting factors are non-zero weighting values, which comprise, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value, wherein the series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block, form an envelope which is omnidirectionally non-linear.       

     The decoder may be such that the P*Q weighting factors are unrelated to each other via any regular mapping rule. 
     The decoder may be such that a mean of maxima of cross correlations between a first series of weighting factors relating to the respective predicted value, and a second series of weighting factors relating to predicted values other than the respective predicted value, or a reversed version of the latter series, whatever leads to a higher maximum, is lower than a predetermined threshold. 
     The decoder may be such that the predetermined threshold is 0.3. 
     The decoder may be such that in the P neighboring samples are located along a one-dimensional path extending along a border of the predetermined block and, for each of the Q predicted values, the series of P weighting factors relating to the respective predicted value are ordered in a manner traversing the one-dimensional path in a predetermined direction. 
     The decoder may be configured to
         derive, for the predetermined block, a prediction residual from the data stream in order to obtain for each of the set of Q predicted values a corresponding residual value, and   reconstruct the predetermined block by correcting each of the set of Q predicted values by the corresponding residual value to obtain a corresponding reconstructed value so that the corresponding reconstructed value depends on the P neighboring samples strictly linearly.       

     The decoder may be such that, wherein
         the decoder is configured to subdivide the picture into a plurality of blocks of different block sizes, which comprise the predetermined block,   wherein the decoder supports, for each of a set of block sizes,
           a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode,   and a second set of intra-prediction modes, wherein for each of the second set of intra-prediction modes, according to the respective intra-prediction mode, a block of the respective block size is predicted by mapping a set of P neighboring samples neighboring the block of the respective block size using an associated linear or affine linear transformation onto a set of Q predicted values for samples of the block of the respective block,   
            wherein, for each block size of the set of block sizes, the associated linear or affine linear transformations of intra-prediction modes within the second set of intra-prediction modes for the respective block size mutually differ and a cardinality of the second set of intra-prediction modes for the block sizes in the set of block sizes coincide, but the associated linear or affine linear transformations of intra-prediction modes within the second set of intra-prediction modes for different block sizes within the set of block sizes are not transferable onto each other by scaling.       

     In accordance to an aspect, there is disclosed a method for decoding a picture from a data stream, comprising:
         mapping a set of P neighboring samples neighboring the predetermined block using a linear or affine linear transformation onto a set of Q predicted values for samples of the predetermined block,   wherein the linear or affine linear transformation comprises P*Q weighting factors among which at least ¼ P*Q weighting factors are non-zero weighting values, which comprise, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value, wherein the series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block, form an envelope which is omnidirectionally non-linear.       

     In accordance to an aspect, there is disclosed an encoder for encoding a data stream from a picture, configured to
         map a set of P neighboring samples neighboring the predetermined block using a linear or affine linear transformation onto a set of Q predicted values for samples of the predetermined block,   wherein the linear or affine linear transformation comprises P*Q weighting factors among which at least ¼ P*Q weighting factors are non-zero weighting values, which comprise, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value, wherein the series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block, form an envelope which is omnidirectionally non-linear.       

     The encoder may be such that the P*Q weighting factors are unrelated to each other via any regular mapping rule. 
     The encoder may be such that a mean of maxima of cross correlations between a first series of weighting factors relating to the respective predicted value, and a second series of weighting factors relating to predicted values other than the respective predicted value, or a reversed version of the latter series, whatever leads to a higher maximum, is lower than a predetermined threshold. 
     The encoder may be configured to use the linear or affine linear transformation for luma component of the predetermined block. 
     In accordance to an aspect, there is disclosed an encoding method, comprising:
         mapping a set of P neighboring samples neighboring the predetermined block using a linear or affine linear transformation onto a set of Q predicted values for samples of the predetermined block,   wherein the linear or affine linear transformation comprises P*Q weighting factors
           among which at least ¼ P*Q weighting factors are non-zero weighting values,   which comprise, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value, wherein the series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block, form an envelope which is omnidirectionally non-linear.   
               

     In accordance to an aspect, there is disclosed a decoder for decoding a picture from a data stream supporting a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction mode, configured to 
     decode a predetermined block of the picture by 
     
         
         
           
             assigning, based on a first signalization in the data stream, the predetermined block to the first set or the second set, 
             sorting the assigned set of intra-prediction modes according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block, to obtain a list of intra prediction modes, 
             deriving, for the predetermined block, from the data stream, an index into the list of intra prediction modes, 
             predicting the predetermined block using an intra prediction mode onto which the index points,
 
wherein decoder is configured to,
 
             if the assigned set is the second set of intra-prediction modes, in sorting the assigned set, use a first mapping which maps each intra-prediction mode of the first set of prediction modes onto a representative one in the second set of intra-prediction modes, and/or 
             if the assigned set is the first set of intra-prediction modes, in sorting the assigned set, use a second mapping which maps each intra-prediction mode of the second set of prediction modes onto a representative one in the first set of intra-prediction modes. 
           
         
       
    
     In accordance to an aspect, there is disclosed a decoder for decoding a picture from a data stream supporting, for each of different block sizes, a set of intra-prediction modes, configured to 
     decode a predetermined block of the picture by 
     
         
         
           
             sorting the set of intra-prediction modes for the block size of the predetermined block according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block, to obtain a list of intra prediction modes, 
             deriving, for the predetermined block, from the data stream, an index into the list of intra prediction modes, 
             predicting the predetermined block using an intra prediction mode onto which the index points,
 
wherein decoder is configured to,
 
             if one of the neighboring blocks is of a different size than the predetermined block in sorting the assigned set, use a mapping which maps each intra-prediction mode of the set of prediction modes for the one neighboring block&#39;s block size onto a representative one in the set of intra-prediction modes for the predetermined block&#39;s block size. 
           
         
       
    
     The decoder may be further configured to decode, from the data stream, the index using a variable length code so that a code length monotonically depends on a rank of the intra-prediction mode in the list of intra-prediction modes the index points to. 
     The decoder may be such that the variable length code is a unary code. 
     The decoder may be configured to sort the assigned set of intra-prediction modes so that the intra-prediction modes within the assigned set of intra-prediction modes used for the neighboring blocks or being targeted by the intra-prediction modes used for the neighboring blocks via the first or second mapping, are put at a beginning of the list. 
     The decoder may be configured to sort the set of intra-prediction modes for the block size of the predetermined block so that the intra-prediction modes within the this set of intra-prediction modes used for the neighboring blocks or being targeted by the intra-prediction modes used for the neighboring blocks via the mapping, are put at a beginning of the list. 
     The decoder may be configured, so that according to each of the second set of intra-prediction modes, the predetermined block is predicted by mapping a set of P neighboring samples neighboring the predetermined block using a linear or affine linear transformation onto a set of Q predicted values for samples of the predetermined block, 
     wherein, for each of the second set of intra-prediction modes, 
     the linear or affine linear transformation comprises PQ weighting factors among which at least ¼ PQ weighting factors are non-zero weighting values, which comprise, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value, wherein the series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block, form an envelope which is omnidirectionally non-linear. 
     The decoder may be configured so that according to each of the set of intra-prediction modes, the predetermined block is predicted by mapping a set of P neighboring samples neighboring the predetermined block using a linear or affine linear transformation onto a set of Q predicted values for samples of the predetermined block, 
     wherein, for each of the second set of intra-prediction modes, the linear or affine linear transformation comprises PQ weighting factors among which at least ¼ PQ weighting factors are non-zero weighting values, which comprise, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value, wherein the series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block, form an envelope which is omnidirectionally non-linear. 
     The decoder may be such that 
     the decoder is configured to subdivide the picture into a plurality of blocks of different block sizes, which comprises the predetermined block, 
     the decoder is configured to support, for each of a set of block sizes, a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction modes, 
     wherein the decoder is configured to, 
     
         
         
           
             if one of the neighboring blocks is of the same block size within the set of block sizes as the predetermined block, but assigned to a different one of the first and second sets of intra-prediction modes, in sorting the assigned set, use the first and second mapping, and 
             if one of the neighboring blocks is of a different block size within the set of block sizes from the predetermined block, in sorting the assigned set, use,
           if the assigned set for the predetermined block is the second set for the predetermined block&#39;s block size while an assigned set for the one neighboring block is the first set for the one neighboring block&#39;s block size, use a third mapping which maps each intra-prediction mode of the first set of prediction modes for the one neighboring block&#39;s block size, onto a representative one in the second set of intra-prediction modes for the predetermined block&#39;s block size, and/or,   if the assigned set for the predetermined block is the first set for the predetermined block&#39;s block size while an assigned set for the one neighboring block is the second set for the one neighboring block&#39;s block size, use a fourth mapping which maps each intra-prediction mode of the second set of prediction modes for the one neighboring block&#39;s block size, onto a representative one in the first set of intra-prediction modes for the predetermined block&#39;s block size, and/or   
         
             if one of the neighboring blocks is of the same block size within the set of block sizes as the predetermined block, if the assigned set for the predetermined block is the second set for the predetermined block&#39;s block size and an assigned set for the one neighboring block is the second set for the one neighboring block&#39;s block size,
           use a fifth mapping which maps each intra-prediction mode of the second set of prediction modes for the one neighboring block&#39;s block size, onto a representative one in the second set of intra-prediction modes for the predetermined block&#39;s block size.   
         
           
         
       
    
     The decoder may be such that 
     the decoder is configured to subdivide the picture into a plurality of blocks of different block sizes, which comprises the predetermined block, 
     the decoder is configured to support, for each of a set of block sizes, a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction modes, 
     wherein decoder is configured to, 
     
         
         
           
             if the predetermined block is non-quadratic, perform the predicting the predetermined block using the intra prediction mode onto which the index points, by
           applying a series of neighboring samples neighboring the predetermined block onto a linear or affine linear transformation associated with the intra prediction mode onto which the index points if the predetermined block is oriented in a first way, and   applying a reversed version of the series of neighboring samples neighboring the predetermined block onto a linear or affine linear transformation associated with an intra prediction mode of the second set of intra-prediction modes other than the linear or affine linear transformation associated with the intra-prediction mode onto which the index points to obtain a predicted block and subsequently transposing the predicted block if the predetermined block is oriented in a second way, perpendicular to the first way.   
         
           
         
       
    
     The decoder may be configured such that 
     wherein the second set of intra-prediction modes comprises a first and a second subsets of intra-prediction modes, and the predetermined block is quadratic, 
     wherein decoder is configured to, 
     
         
         
           
             perform the predicting the predetermined block using the intra prediction mode onto which the index, by
           applying a series of neighboring samples neighboring the predetermined block onto a linear or affine linear transformation associated with the intra prediction mode onto which the index points if the intra prediction mode onto which the index points is comprised by the first subset, and   applying a reversed version of the series of neighboring samples neighboring the predetermined block onto a linear or affine linear transformation associated with an intra prediction mode of the first subset of intra-prediction modes to obtain a predicted block and subsequently transposing the predicted block if the intra prediction mode onto which the index points is comprised by the second subset.   
         
           
         
       
    
     The decoder may be such that for at least one of the intra-prediction modes of the second set, the prediction using the one intra-prediction mode involves predicting the predetermined block from spatial domain to transform domain or transform domain to transform domain. 
     Decoder may be configured to use a transformation of the first or second set for the luma component and a transformation of the first set for the chroma component. 
     Decoder may be configured to map a mode of the second set used for a luma component into a mode of the first set for the luma component. 
     Decoder may be such that the second mapping maps a plurality of modes of the second set into a single mode of the first set. 
     Decoder may be such that the second mapping maps all the modes of the second set into a single mode of the first set. 
     Decoder may be such that the single mode of the first set is the planar mode. 
     In accordance to an aspect, there is disclosed a method for decoding a picture from a data stream supporting a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction mode, the method comprising: 
     decoding a predetermined block of the picture by 
     
         
         
           
             assigning, based on a first signalization in the data stream, the predetermined block to the first set or the second set, 
             sorting the assigned set of prediction modes according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block to obtain a list of intra prediction modes, 
             deriving, for the predetermined block, from the data stream, an index into the list of intra prediction modes, 
             predicting the predetermined block using an intra prediction mode onto which the index points,
 
wherein decoding is based on,
 
             if the assigned set is the second set of intra-prediction modes, in sorting the assigned set, use a first mapping which maps each intra-prediction mode of the first set of prediction modes onto a representative one in the second set of intra-prediction modes, and/or 
             if the assigned set is the first set of intra-prediction modes, in sorting the assigned set, use a second mapping which maps each intra-prediction mode of the second set of prediction modes onto a representative one in the first set of intra-prediction modes. 
           
         
       
    
     In accordance to an aspect, there is disclosed an encoder for encoding a picture on a data stream supporting a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction mode, configured to 
     encode a predetermined block of the picture by 
     
         
         
           
             assigning, and encoding on a first signalization in the data stream, the predetermined block to the first set or the second set, 
             sorting the assigned set of prediction modes according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block to obtain a list of intra prediction modes, 
             determining, for the predetermined block, from the data stream, an index into the list of intra prediction modes, 
             predicting the predetermined block using an intra prediction mode onto which the index points,
 
wherein the encoder is configured to,
 
             if the assigned set is the second set of intra-prediction modes, in sorting the assigned set, use a first mapping which maps each intra-prediction mode of the first set of prediction modes onto a representative one in the second set of intra-prediction modes, and/or 
             if the assigned set is the first set of intra-prediction modes, in sorting the assigned set, use a second mapping which maps each intra-prediction mode of the second set of prediction modes onto a representative one in the first set of intra-prediction modes. 
           
         
       
    
     In accordance to an aspect, there is disclosed an encoder for encoding a picture onto a data stream supporting, for each of different block sizes, a set of intra-prediction modes, configured to 
     encode a predetermined block of the picture by 
     
         
         
           
             sorting the set of intra-prediction modes for the block size of the predetermined block according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block to obtain a list of intra prediction modes, 
             inserting, for the predetermined block, into the data stream, an index into the list of intra prediction modes, 
             predicting the predetermined block using an intra prediction mode onto which the index points,
 
wherein encoder is configured to,
 
             if one of the neighboring blocks is a different size than the predetermined block, in sorting the assigned set, use a mapping which maps each intra-prediction mode of the set of prediction modes for the one neighboring block&#39;s block size onto a representative one in the set of intra-prediction modes for the predetermined block&#39;s block size. 
           
         
       
    
     The encoder may be further configured to encode in the data stream the index using a variable length code so that a code length monotonically depends on a rank of the intra-prediction mode in the list of intra-prediction modes the index points to. 
     The encoder may be such that the variable length code is a unary code. 
     The encoder may be configured to sort the prediction modes according to their probability and/or historical data regarding the previous uses for other blocks. 
     The encoder may be configured to write a second signalization in the data stream with a first symbol continuously repeated up to a second symbol, so as to derive the index in the list on the basis of the length of the symbol repetitions. 
     The encoder may be configured to sort the assigned set of intra-prediction modes so that the intra-prediction modes within the assigned set of intra-prediction modes used for the neighboring blocks or being targeted by the intra-prediction modes used for the neighboring blocks via the first or second mapping, are put at a beginning of the list. 
     The encoder may be configured to sort the set of intra-prediction modes for the block size of the predetermined block so that the intra-prediction modes within the this set of intra-prediction modes used for the neighboring blocks or being targeted by the intra-prediction modes used for the neighboring blocks via the mapping, are put at a beginning of the list. 
     The encoder may be configured so that, according to each of the second set of intra-prediction modes, the predetermined block is predicted by mapping a set of P neighboring samples neighboring the predetermined block using a linear or affine linear transformation onto a set of Q predicted values for samples of the predetermined block, 
     Wherein, for each of the second set of intra-prediction modes, 
     the linear or affine linear transformation comprises PQ weighting factors 
     
         
         
           
             among which at least ¼ P*Q weighting factors are non-zero weighting values, 
             which comprise, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value, wherein the series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block, form an envelope which is omnidirectionally non-linear. 
           
         
       
    
     The encoder may be configured, so that according to each of the set of intra-prediction modes, the predetermined block is predicted by mapping a set of P neighboring samples neighboring the predetermined block using a linear or affine linear transformation onto a set of Q predicted values for samples of the predetermined block, 
     Wherein, for each of the second set of intra-prediction modes, 
     the linear or affine linear transformation comprises P*Q weighting factors 
     
         
         
           
             among which at least ¼ P*Q weighting factors are non-zero weighting values, 
             which comprise, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value, wherein the series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block, form an envelope which is omnidirectionally non-linear. 
           
         
       
    
     The encoder may be such that the encoder is configured to subdivide the picture into a plurality of blocks of different block sizes, which comprises the predetermined block, the encoder is configured to support, for each of a set of block sizes, a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction modes, 
     wherein the encoder is configured to, 
     
         
         
           
             if one of the neighboring blocks is of the same block size within the set of block sizes as the predetermined block, but assigned to a different one of the first and second sets of intra-prediction modes, in sorting the assigned set, use the first and second mapping, and 
             if one of the neighboring blocks is of a different block size within the set of block sizes from the predetermined block, (e.g. they are not the same) in sorting the assigned set, use,
           if the assigned set for the predetermined block is the second set for the predetermined block&#39;s block size while an assigned set for the one neighboring block is the first set for the one neighboring block&#39;s block size, use a third mapping which maps each intra-prediction mode of the first set of prediction modes for the one neighboring block&#39;s block size, onto a representative one in the second set of intra-prediction modes for the predetermined block&#39;s block size, and/or,   if the assigned set for the predetermined block is the first set for the predetermined block&#39;s block size while an assigned set for the one neighboring block is the second set for the one neighboring block&#39;s block size, use a fourth mapping which maps each intra-prediction mode of the second set of prediction modes for the one neighboring block&#39;s block size, onto a representative one in the first set of intra-prediction modes for the predetermined block&#39;s block size, mapping and/or   
         
             if one of the neighboring blocks is of the same block size within the set of block sizes as the predetermined block, if the assigned set for the predetermined block is the second set for the predetermined block&#39;s block size and an assigned set for the one neighboring block is the second set for the one neighboring block&#39;s block size,
           use a fifth mapping which maps each intra-prediction mode of the second set of prediction modes for the one neighboring block&#39;s block size, onto a representative one in the second set of intra-prediction modes for the predetermined block&#39;s block size.   
         
           
         
       
    
     The encoder may be such that 
     the encoder is configured to subdivide the picture into a plurality of blocks of different block sizes, which comprises the predetermined block, 
     the encoder is configured to support, for each of a set of block sizes, a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction modes, 
     wherein encoder is configured to, 
     
         
         
           
             if the predetermined block is non-quadratic, perform the predicting the predetermined block using the intra prediction mode onto which the index points, by
           applying a series of neighboring samples neighboring the predetermined block onto a linear or affine linear transformation associated with the intra prediction mode onto which the index points if the predetermined block is oriented in a first way, and   applying a reversed version of the series of neighboring samples neighboring the predetermined block onto a linear or affine linear transformation associated with an intra prediction mode of the second set of intra-prediction modes other than the linear or affine linear transformation associated with the intra-prediction mode onto which the index points to obtain a predicted block and subsequently transposing the predicted block if the predetermined block is oriented in a second way, perpendicular to the first way.   
         
           
         
       
    
     The encoder may be such that 
     the second set of intra-prediction modes comprises a first and a second subsets of intra-prediction modes, and the predetermined block is quadratic 
     wherein the encoder is configured to, 
     
         
         
           
             perform the predicting the predetermined block using the intra prediction mode onto which the index points, by
           applying a series of neighboring samples neighboring the predetermined block onto a linear or affine linear transformation associated with the intra prediction mode onto which the index points if the intra prediction mode onto which the index points is comprised by the first subset, and   applying a reversed version of the series of neighboring samples neighboring the predetermined block onto a linear or affine linear transformation associated with an intra prediction mode of the second subset of intra-prediction modes to obtain a predicted block and subsequently transposing the predicted block if the intra prediction mode onto which the index points is comprised by the second subset.   
         
           
         
       
    
     The encoder may be such that for at least one of the intra-prediction modes of the second set, the prediction using the one intra-prediction mode involves predicting the predetermined block from spatial domain to transform domain or transform domain to transform domain. 
     In accordance to an aspect, there is disclosed a method for encoding a picture on a data stream supporting a first set of intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode, and a second set of intra-prediction mode, comprising
         assigning, and encoding on a first signalization in the data stream, the predetermined block to the first set or the second set,   sorting the assigned set of prediction modes according to intra-prediction modes used for neighboring blocks, neighboring the predetermined block to obtain a list of intra prediction modes,   determining, for the predetermined block, from the data stream, an index into the list of intra prediction modes,   predicting the predetermined block using an intra prediction mode onto which the index points,   encoding the data stream,
 
wherein the encoder is configured to,
   if the assigned set is the second set of intra-prediction modes, in sorting the assigned set, use a first mapping which maps each intra-prediction mode of the first set of prediction modes onto a representative one in the second set of intra-prediction modes, and/or   if the assigned set is the first set of intra-prediction modes, in sorting the assigned set, use a second mapping which maps each intra-prediction mode of the second set of prediction modes onto a representative one in the first set of intra-prediction modes.       

     In accordance to an aspect, there is disclosed a method for decoding a picture from a data stream, configured to 
     predict a predetermined block of the picture by 
     
         
         
           
             subjecting a first set of neighboring samples, which neighbor the predetermined block at a first side of the predetermined block, to a transformation [e.g., FFT, DCT . . . ] to obtain a first set of transform coefficients, and/or subjecting a second set of neighboring samples, which neighbor the predetermined block at a second side of the predetermined block, to a transformation to obtain a second set of transform coefficients, 
             subjecting a combination of the first and second sets of transform coefficients or a combination of the first set of neighboring samples, and the second set of transform coefficients or a combination of the second set of neighboring samples, and the first set of transform coefficients to a linear or affine linear transformation. 
           
         
       
    
     Decoder may be configured to
         Subdivide the picture into a plurality of blocks of different sizes which includes the predetermined block,   Locate the first and second sets of neighboring samples in a manner independent from sizes of neighboring blocks which include the first and second sets of neighboring samples.
 
[We do not necessarily take the whole block but only the stripe] Decoder may be configured to
 
Locate the first and second sets of neighboring samples in a manner so that the first and second sets of neighboring samples are located along a one-dimensional path alongside the first and second sides, respectively, wherein the first and second sets of transform coefficients represent one-dimensional transforms.
   Decoder may be configured to form the combination of the first and second sets of transform coefficients by grabbing a first proper subset of the transform coefficients out of the first set of transform coefficients and/or a second proper subset of the transform coefficients out of the second set of transform coefficients so that the combination is independent from a non-grabbed portion of the first and/or second set of transform coefficients, respectively.   Decoder may be configured so that the subjecting the combination of the first and second sets of transform coefficients to the linear or affine linear transformation yields a predictor of the predetermined block in transform domain.   Decoder may be configured so that the subjecting the combination of the first and second sets of transform coefficients to the linear or affine linear transformation yields a predicted value for a proper subset of transform coefficients of a transform of the predetermined block [while e.g. the other are set to zero by default].
           Decoder may be configured so that the subjecting the combination of the first and second sets of transform coefficients to the linear or affine linear transformation yields a predictor of the predetermined block in spatial domain. In accordance to an aspect, there is disclosed a method for decoding a picture from a data stream, comprising
 
predicting a predetermined block of the picture by
   
           subjecting a first set of neighboring samples, which neighbor the predetermined block at a first side of the predetermined block, to a transformation [e.g., FFT, DCT . . . ] to obtain a first set of transform coefficients, and/or subjecting a second set of neighboring samples, which neighbor the predetermined block at a second side of the predetermined block, to a transformation to obtain a second set of transform coefficients,   subjecting a combination of the first and second sets of transform coefficients or a combination of the first set of neighboring samples, and the second set of transform coefficients or a combination of the second set of neighboring samples, and the first set of transform coefficients to a linear or affine linear transformation.
 
[e.g., we transform each of the portions from the spatial domain to a transform domain and only thereafter we apply the (e.g., linear or affine) transformation].
       

     In accordance to an aspect, there is disclosed an encoder for encoding a picture onto a data stream, configured to 
     predict a predetermined block of the picture by 
     
         
         
           
             subjecting a first set of neighboring samples, which neighbor the predetermined block at a first side of the predetermined block, to a transformation [e.g., FFT, DCT . . . ] to obtain a first set of transform coefficients, and/or subjecting a second set of neighboring samples, which neighbor the predetermined block at a second side of the predetermined block, to a transformation to obtain a second set of transform coefficients, 
             subjecting a combination of the first and second sets of transform coefficients or a combination of the first set of neighboring samples, and the second set of transform coefficients or a combination of the second set of neighboring samples, and the first set of transform coefficients to a linear or affine linear transformation.
 
e.g., we transform each of the portions from the spatial domain to a transform domain and only thereafter we apply the (e.g., linear or affine) transformation]
 
           
         
       
    
     Encoder may be configured to
         Subdivide the picture into a plurality of blocks of different sizes which includes the predetermined block,   Locate the first and second sets of neighboring samples in a manner independent from sizes of neighboring blocks which include the first and second sets of neighboring samples.       

     Encoder may be configured to 
     Locate the first and second sets of neighboring samples in a manner so that the first and second sets of neighboring samples are located along a one-dimensional path alongside the first and second sides, respectively, wherein the first and second sets of transform coefficients represent one-dimensional transforms.
         Encoder may be configured to form the combination of the first and second sets of transform coefficients by grabbing a first proper subset of the transform coefficients out of the first set of transform coefficients and/or a second proper subset of the transform coefficients out of the second set of transform coefficients so that the combination is independent from a non-grabbed portion of the first and/or second set of transform coefficients, respectively.   Encoder may be configured so that the subjecting the combination of the first and second sets of transform coefficients to the linear or affine linear transformation yields a predictor of the predetermined block in transform domain.   Encoder may be configured so that the subjecting the combination of the first and second sets of transform coefficients to the linear or affine linear transformation yields a predicted value for a proper subset of transform coefficients of a transform of the predetermined block.   Encoder may be configured so that the subjecting the combination of the first and second sets of transform coefficients to the linear or affine linear transformation yields a predictor of the predetermined block in spatial domain.       

     In accordance to an aspect, there is disclosed a method for encoding a picture from a data stream, comprising 
     predicting a predetermined block of the picture by 
     
         
         
           
             subjecting a first set of neighboring samples, which neighbor the predetermined block at a first side of the predetermined block, to a transformation [e.g., FFT, DCT . . . ] to obtain a first set of transform coefficients, and/or subjecting a second set of neighboring samples, which neighbor the predetermined block at a second side of the predetermined block, to a transformation to obtain a second set of transform coefficients, 
             subjecting a combination of the first and second sets of transform coefficients or a combination of the first set of neighboring samples, and the second set of transform coefficients or a combination of the second set of neighboring samples, and the first set of transform coefficients to a linear or affine linear transformation.
 
[e.g., we transform each of the portions from the spatial domain to a transform domain and only thereafter we apply the (e.g., linear or affine) transformation].
 
           
         
       
    
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which: 
         FIGS.  1  and  2    shows apparatus to block-wise encode an image. 
         FIGS.  3  and  4    shows apparatus to block-wise decode an image. 
         FIG.  5    shows a predetermined block to be predicted. 
         FIG.  6    shows a prediction operation. 
         FIG.  7    shows a diagram illustrating a conventional prediction. 
         FIG.  8    partially shows a datastream. 
         FIG.  9    shows indexes to be used in examples. 
         FIG.  10   a    (which is subdivided into  FIGS.  10   a   ′,  10   a ″, and  10   a ′″) and  FIGS.  10   b  to  10   e    show techniques for mapping between different modes. 
         FIGS.  11   a  and  11   b    show examples of procedures. 
         FIGS.  11   c  and  11   d    show examples of mapping. 
         FIG.  12    (which is subdivided into  FIGS.  12   ′,  12 ″,  12 ′″, and  12 ″″) and  FIG.  13    show examples of procedures. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Encoders, Decoders According to Examples 
     In the following, various examples are described which assist in achieving a more effective compression when using intra-prediction. Some examples achieve the compression efficiency increase by spending a set of intra-prediction modes. The latter ones may be added to other intra-prediction modes heuristically designed, for instance, or may be provided exclusively. And even other examples make use of both of the just-discussed specialties. 
     In order to ease the understanding of the following examples of the present application, the description starts with a presentation of possible encoders and decoders fitting thereto into which the subsequently outlined examples of the present application could be built. 
       FIG.  1    shows an apparatus for block-wise encoding a picture  10  into a datastream  12  (also indicated as  80  in some examples, see below). The apparatus is indicated using reference sign  14  and may be a still picture encoder or a video encoder. In other words, picture  10  may be a current picture out of a video  16  when the encoder  14  is configured to encode video  16  including picture  10  into datastream  12 , or encoder  14  may encode picture  10  into datastream  12  exclusively. Examples below may make use of the apparatus  14 . 
     As mentioned, encoder  14  performs the encoding in a block-wise manner or block-base. To this, encoder  14  subdivides picture  10  into blocks, units of which encoder  14  encodes picture  10  into datastream  12 . Examples of possible subdivisions of picture  10  into blocks  18  are set out in more detail below. Generally, the subdivision may end-up into blocks  18  of constant size such as an array of blocks arranged in rows and columns or into blocks  18  of different block sizes such as by use of a hierarchical multi-tree subdivisioning with starting the multi-tree subdivisioning from the whole picture area of picture  10  or from a pre-partitioning of picture  10  into an array of tree blocks wherein these examples shall not be treated as excluding other possible ways of subdivisioning picture  10  into blocks  18 . 
     Further, encoder  14  is a predictive encoder configured to predictively encode picture  10  into datastream  12 . For a certain block  18  this means that encoder  14  determines a prediction signal for block  18  and encodes the prediction residual, i.e. the prediction error at which the prediction signal deviates from the actual picture content within block  18 , into datastream  12 . 
     Encoder  14  may support different prediction modes so as to derive the prediction signal for a certain block  18 . The prediction modes, which are of importance in the following examples, are intra-prediction modes according to which the inner of block  18  is predicted spatially from neighboring, already encoded samples of picture  10 . The encoding of picture  10  into datastream  12  and, accordingly, the corresponding decoding procedure, may be based on a certain coding order  20  defined among blocks  18 . For instance, the coding order  20  may traverse blocks  18  in a raster scan order such as row-wise from top to bottom with traversing each row from left to right, for instance. In case of hierarchical multi-tree based subdivisioning, raster scan ordering may be applied within each hierarchy level, wherein a depth-first traversal order may be applied, i.e. leaf notes within a block of a certain hierarchy level may precede blocks of the same hierarchy level having the same parent block according to coding order  20 . Depending on the coding order  20 , neighboring, already encoded samples of a block  18  may be located usually at one or more sides of block  18 . In case of the examples presented herein, for instance, neighboring, already encoded samples of a block  18  are located to the top of, and to the left of block  18 . 
     Intra-prediction modes may not be the only ones supported by encoder  14 . In case of encoder  14  being a video encoder, for instance, encoder  14  may also support intra-prediction modes according to which a block  18  is temporarily predicted from a previously encoded picture of video  16 . Such an intra-prediction mode may be a motion-compensated prediction mode according to which a motion vector is signaled for such a block  18  indicating a relative spatial offset of the portion from which the prediction signal of block  18  is to be derived as a copy. Additionally or alternatively, other non-intra-prediction modes may be available as well such as inter-view prediction modes in case of encoder  14  being a multi-view encoder, or non-predictive modes according to which the inner of block  18  is coded as is, i.e. without any prediction. 
     Before starting with focusing the description of the present application onto intra-prediction modes, a more specific example for a possible block-based encoder, i.e. for a possible implementation of encoder  14 , as described with respect to  FIG.  2    with then presenting two corresponding examples for a decoder fitting to  FIGS.  1  and  2   , respectively. 
       FIG.  2    shows a possible implementation of encoder  14  of  FIG.  1   , namely one where the encoder is configured to use transform coding for encoding the prediction residual although this is nearly an example and the present application is not restricted to that sort of prediction residual coding. According to  FIG.  2   , encoder  14  (which may be used for examples below) may comprise a subtractor  22  configured to subtract from the inbound signal, i.e. picture  10  or, on a block basis, current block  18 , the corresponding prediction signal  24  so as to obtain the prediction residual signal  26  which is then encoded by a prediction residual encoder  28  into a datastream  12 . The prediction residual encoder  28  is composed of a lossy encoding stage  28   a  and a lossless encoding stage  28   b . The lossy stage  28   a  receives the prediction residual signal  26  and comprises a quantizer  30  which quantizes the samples of the prediction residual signal  26 . As already mentioned above, the present example uses transform coding of the prediction residual signal  26  and accordingly, the lossy encoding stage  28   a  comprises a transform stage  32  connected between subtractor  22  and quantizer  30  so as to transform such a spectrally decomposed prediction residual  26  with a quantization of quantizer  30  taking place on the transformed coefficients where presenting the residual signal  26 . The transform may be a DCT, DST, FFT, Hadamard transform or the like. The transformed and quantized prediction residual signal  34  is then subject to lossless coding by the lossless encoding stage  28   b  which is an entropy coder entropy coding quantized prediction residual signal  34  into datastream  12 . Encoder  14  further comprises the prediction residual signal reconstruction stage  36  connected to the output of quantizer  30  so as to reconstruct from the transformed and quantized prediction residual signal  34  the prediction residual signal in a manner also available at the decoder, i.e. taking the coding loss is quantizer  30  into account. To this end, the prediction residual reconstruction stage  36  comprises a dequantizer  38  which perform the inverse of the quantization of quantizer  30 , followed by an inverse transformer  40  which performs the inverse transformation relative to the transformation performed by transformer  32  such as the inverse of the spectral decomposition such as the inverse to any of the above-mentioned specific transformation examples. Encoder  14  comprises an adder  42  which adds the reconstructed prediction residual signal as output by inverse transformer  40  and the prediction signal  24  so as to output a reconstructed signal, i.e. reconstructed samples. This output is fed into a predictor  44  of encoder  14  which then determines the prediction signal  24  based thereon. It is predictor  44  which supports all the prediction modes already discussed above with respect to  FIG.  1   .  FIG.  2    also illustrates that in case of encoder  14  being a video encoder, encoder  14  may also comprise an in-loop filter  46  with filters completely reconstructed pictures which, after having been filtered, form reference pictures for predictor  44  with respect to inter-predicted block. 
     As already mentioned above, encoder  14  operates block-based. For the subsequent description, the block bases of interest is the one subdividing picture  10  into blocks for which the intra-prediction mode is selected out of a set or plurality of intra-prediction modes supported by predictor  44  or encoder  14 , respectively, and the selected intra-prediction mode performed individually. Other sorts of blocks into which picture  10  is subdivided may, however, exist as well. For instance, the above-mentioned decision whether picture  10  is inter-coded or intra-coded may be done at a granularity or in units of blocks deviating from blocks  18 . For instance, the inter/intra mode decision may be performed at a level of coding blocks into which picture  10  is subdivided, and each coding block is subdivided into prediction blocks. Prediction blocks with encoding blocks for which it has been decided that intra-prediction is used, are each subdivided to an intra-prediction mode decision. To this, for each of these prediction blocks, it is decided as to which supported intra-prediction mode should be used for the respective prediction block. These prediction blocks will form blocks  18  which are of interest here. Prediction blocks within coding blocks associated with inter-prediction would be treated differently by predictor  44 . They would be inter-predicted from reference pictures by determining a motion vector and copying the prediction signal for this block from a location in the reference picture pointed to by the motion vector. Another block subdivisioning pertains to the subdivisioning into transform blocks at units of which the transformations by transformer  32  and inverse transformer  40  are performed. Transformed blocks may, for instance, be the result of further subdivisioning coding blocks. Naturally, the examples set out herein should not be treated as being limiting and other examples exist as well. For the sake of completeness only, it is noted that the subdivisioning into coding blocks may, for instance, use multi-tree subdivisioning, and prediction blocks and/or transform blocks may be obtained by further subdividing coding blocks using multi-tree subdivisioning, as well. 
     A decoder or apparatus (e.g., used in present examples) for block-wise decoding fitting to the encoder  14  of  FIG.  1    is depicted in  FIG.  3   . This decoder  54  does the opposite of encoder  14 , i.e. it decodes from datastream  12  picture  10  in a block-wise manner and supports, to this end, a plurality of intra-prediction modes. The decoder  54  may comprise a residual provider  156 , for example. All the other possibilities discussed above with respect to  FIG.  1    are valid for the decoder  54 , too. To this, decoder  54  may be a still picture decoder or a video decoder and all the prediction modes and prediction possibilities are supported by decoder  54  as well. The difference between encoder  14  and decoder  54  lies, primarily, in the fact that encoder  14  chooses or selects coding decisions according to some optimization such as, for instance, in order to minimize some cost function which may depend on coding rate and/or coding distortion. One of these coding options or coding parameters may involve a selection of the intra-prediction mode to be used for a current block  18  among available or supported intra-prediction modes. The selected intra-prediction mode may then be signaled by encoder  14  for current block  18  within datastream  12  with decoder  54  redoing the selection using this signalization in datastream  12  for block  18 . Likewise, the subdivisioning of picture  10  into blocks  18  may be subject to optimization within encoder  14  and corresponding subdivision information may be conveyed within datastream  12  with decoder  54  recovering the subdivision of picture  10  into blocks  18  on the basis of the subdivision information. Summarizing the above, decoder  54  may be a predictive decoder operating on a block-bases and besides intra-prediction modes, decoder  54  may support other prediction modes such as inter-prediction modes in case of, for instance, decoder  54  being a video decoder. In decoding, decoder  54  may also use the coding order  20  discussed with respect to  FIG.  1    and as this coding order  20  is obeyed both at encoder  14  and decoder  54 , the same neighboring samples are available for a current block  18  both at encoder  14  and decoder  54 . Accordingly, in order to avoid unnecessary repetition, the description of the mode of operation of encoder  14  shall also apply to decoder  54  as far the subdivision of picture  10  into blocks is concerned, for instance, as far as prediction is concerned and as far as the coding of the prediction residual is concerned. Differences lie in the fact that encoder  14  chooses, by optimization, some coding options or coding parameters and signals within, or inserts into, datastream  12  the coding parameters which are then derived from the datastream  12  by decoder  54  so as to redo the prediction, subdivision and so forth. 
       FIG.  4    shows a possible implementation of the decoder  54  of  FIG.  3    (e.g., used in present examples), namely one fitting to the implementation of encoder  14  of  FIG.  1    as shown in  FIG.  2   . As many elements of the encoder  54  of  FIG.  4    are the same as those occurring in the corresponding encoder of  FIG.  2   , the same reference signs, provided with an apostrophe, are used in  FIG.  4    in order to indicate these elements. In particular, adder  42 ′, optional in-loop filter  46 ′ and predictor  44 ′ are connected into a prediction loop in the same manner that they are in encoder of  FIG.  2   . The reconstructed, i.e. dequantized and retransformed prediction residual signal applied to added  42 ′ is derived by a sequence of entropy decoder  56  which inverses the entropy encoding of entropy encoder  28   b , followed by the residual signal reconstruction stage  36 ′ which is composed of dequantizer  38 ′ and inverse transformer  40 ′ just as it is the case on encoding side. The decoder&#39;s output is the reconstruction of picture  10 . The reconstruction of picture  10  may be available directly at the output of adder  42 ′ or, alternatively, at the output of in-loop filter  46 ′. Some post-filter may be arranged at the decoder&#39;s output in order to subject the reconstruction of picture  10  to some post-filtering in order to improve the picture quality, but this option is not depicted in  FIG.  4   . 
     Again, with respect to  FIG.  4    the description brought forward above with respect to  FIG.  2    shall be valid for  FIG.  4    as well with the exception that merely the encoder performs the optimization tasks and the associated decisions with respect to coding options. However, all the description with respect to block-subdivisioning, prediction, dequantization and retransforming is also valid for the decoder  54  of  FIG.  4   . 
     Examples 
     In some examples above and below, the encoder and/or decoder may be so as to reconstruct the predetermined block ( 18 ) by correcting each of the set of Q predicted values by the corresponding residual value to obtain a corresponding reconstructed value so that the corresponding reconstructed value ( 24 ′) depends on the P neighboring samples (template) strictly linearly (except for, optionally, a clipping applied after prediction correction). 
     In some cases, it is possible to refer to a “set of block sizes”, which includes the different sizes that may be used For example, a size M×N is a size different from M×N of M×N 1  if N≠N 1 . Some modes are only directed to a particular block size (which is one of the block sizes of the set of block sizes). 
     Further, reference is made to a “first set  121  of conventional modes”, which contains conventional modes. Reference is also made to a “second set  122  of ALWIP modes”, which contains the ALWIP mode(s) (examples of ALWIP are provided below). 
     The present document is concerned, inter alia, with an improved intra-prediction mode concept for block-wise picture coding such as usable in a video codec such as HEVC or any successor of HEVC. 
     Intra-prediction modes are widely used in picture and video coding. In video coding, intra-prediction modes compete with other prediction modes such as inter-prediction modes such as motion-compensated prediction modes. In intra-prediction modes, a current block is predicted on the basis of neighboring samples, i.e. samples already encoded as far as the encoder side is concerned, and already decoded as far as the decoder side is concerned. Neighboring sample values are extrapolated into the current block so as to form a prediction signal for the current block with the prediction residual being transmitted in the datastream for the current block. The better the prediction signal is, the lower the prediction residual is and, accordingly, a lower number of bits may be used to code the prediction residual. 
     In order to be effective, several aspects should be taken into account in order to form an effective frame work for intra-prediction in a block-wise picture coding environment. For instance, the larger the number of intra-prediction modes supported by the codec, the larger the side information rate consumption is in order to signal the selection to the decoder. On the other hand, the set of supported intra-prediction modes should be able to provide a good prediction signal, i.e. a prediction signal resulting in a low prediction residual. 
     There is disclosed apparatus and methods for block-wise decoding (or encoding) a picture (e.g., 10) from a data stream (e.g., 12, 80), the apparatus and the methods supporting at least one intra-prediction mode according to which the intra-prediction signal for a block of a predetermined size of the picture is determined by applying a first template of samples which neighbors the current block onto an affine linear predictor which, in the sequel, shall be called Affine Linear Weighted Intra Predictor (ALWIP). 
     The apparatus and methods may have at least one of the properties discussed below. 
     Examples of Predictors Complementary to Other Predictors 
     The intra-prediction modes supported by the present apparatus and methods may, in some examples, be complementary to other intra prediction modes of the codec. They may be complementary to the DC-, Planar-, or Angular-Prediction modes defined in the HEVC codec resp. the JEM reference software. The latter three types of intra-prediction modes shall be called “conventional intra prediction modes” here. Thus, for a given block in intra mode, a flag (e.g. encoded in the field subsequently indicated with “81”) may be parsed by the decoder which indicates whether one of the intra-prediction modes supported by the apparatus or method is to be used or not. 
     More than One Proposed Prediction Modes 
     The apparatus and methods may contain more than one ALWIP mode, e.g., stored in storage units (or in some cases, they may be obtained on-the-fly). Thus, in case that the decoder knows that one of the ALWIP modes supported by the encoder apparatus is to be used, the decoder may parse additional information (e.g., encoded in the field subsequently indicated with “82”) that may indicate which of the ALWIP modes supported by the apparatus of method is to be used. 
     The signalization of the mode supported may have the property that the coding of some ALWIP modes may involve less bins than other ALWIP modes. Which of these modes involve less bins and which modes involve more bins may either depend on information that can be extracted from the already decoded bitstream  12  (or  80 ) or may be fixed in advance. 
     Sharing Predictors Between Different Block Sizes Using Downsampling/Upsampling 
     Some examples discussed here may be exemplified in particular by taking into consideration examples of  FIG.  13    (see also the discussion below). 
     In some cases, an encoder or decoder may perform transformations between predictors of different block sizes, e.g. by downsampling and/or upsampling. This may happen when an ALWIP mode is provided for a particular size (e.g., M×N), while a block (e.g., 18 or B 1 ) to be predicted has dimension M 1 ×N 1  different from M×N (e.g., at least one of M and N is such that M≠M 1  and or N≠N 1 ). Hereinbelow, the “second template  1160 ” may refer to a group of already-predicted neighboring samples (also indicated with  17 ′ a ,  17 ′ b ,  17 ′ c , see below) used for performing the intra prediction, associated to a block size for which no ALWIP mode is at disposal of the encoder or decoder. The “first template  1161 ” may refer to a template with the dimensions that may be used for a prediction associated to a block size for which an ALWIP mode is actually at disposal of the encoder or decoder. Examples are here discussed which permit to “jump” from the second template  1160  to the first template  1161 , to subsequently perform the prediction using the first template  1161 , and to finally return to the original block size after having predicted the block  18  (B 1 ). 
     With reference to  FIG.  13   , the apparatus and methods may be configured, for a current block  18  (B 1 ) differing from a predetermined size for which an ALWIP mode is provided to the decoder (or encoder), to:
         resample the second template ( 1160 ) of samples ( 17 ′ a ,  17 ′ b ,  17 ′ c ) neighboring the current block (B 1 ,  18 ), so as to conform with the first template ( 1161 ), so as to obtain a resampled template ( 1136 );   apply the resampled template ( 1161 ) onto an ALWIP predictor ( 1138   a ) so as to obtain a preliminary intra-prediction; and   resample ( 1140 ) the preliminary intra-prediction signal so as to conform with the current block so as to obtain the intra-prediction signal for the current block ( 18 ).       

     The apparatus may be configured to resample by downsampling (D) the second template ( 1160 ) to obtain the first template ( 1161 ). 
     The apparatus may be configured to resample the preliminary intra-prediction signal by upsampling the preliminary intra-prediction signal. The apparatus may be configured to transform the preliminary intra-prediction signal from a spatial domain into a transform domain; and resample the preliminary intra-prediction signal in the transform domain. The apparatus may be configured to resample the transform-domain preliminary intra-prediction signal by scaling the coefficients of the preliminary intra-prediction signal. 
     Apparatus or methods may be configured, in some examples, to
         resample a transform-domain preliminary intra-prediction signal by:
           increasing the dimensions of the intra-prediction signal to conform to the dimensions of the current block; and   zero-padding the coefficients of added coefficients of the preliminary intra-prediction signal, the added coefficients relating to higher-frequencies bins.   
               

     The apparatus may be configured to compose the transform-domain preliminary intra-prediction signal with a dequantized version of a prediction residual signal. The apparatus may be configured to resample the preliminary intra-prediction signal in the spatial domain. 
     The apparatus may be configured to resample the preliminary intra-prediction signal by performing a bilinear interpolation. The apparatus may be configured to encode in a data field information regarding the resampling and/or the use of affine linear predictors for different dimensions. 
     In some cases, it is possible to us a mapping which maps a mode which might be used for the M 1 ×N 1  block  18  (B 1 ) into the mode  1138   a.    
     The present example has been explained for ALWIP modes, but it may also be implemented for conventional modes or for other kinds of modes. 
     Prediction into the Transform Domain 
     As will be apparent in subsequent passages (see also  FIG.  12   ), it is possible to perform the intra prediction in the spatial domain and/or in the transform domain. Hereinafter there are some considerations according to an encoder apparatus and/or decoder apparatus in the transform domain. 
     There is also disclosed an apparatus for block-wise decoding a picture from a data stream, the apparatus supporting at least one intra-prediction mode according to which the intra-prediction signal for a current block of the picture is determined by:
         applying a first set of neighboring samples of the current block onto a ALWIP to obtain a prediction of a set of transform coefficients of a transform of the current block.       

     One of the apparatus may be configured to inversely transform the prediction to obtain a reconstructed signal. One of the apparatus may be configured to decode from the data stream an index using a variable length code; and perform the selection using the index. One of the apparatus may be configured to determine a ranking of the set of intra prediction modes; and, subsequently, resample the second template. 
     There is disclosed a method comprising:
         resampling a second template of samples neighboring the current block, so as to conform with a first template so as to obtain a resampled template,   applying the resampled template of samples onto a ALWIP so as to obtain a preliminary intra-prediction signal, and   resampling the preliminary intra-prediction signal so as to conform with the current block so as to obtain the intra-prediction signal for the current block.       

     There is disclosed a method for block-wise decoding a picture from a data stream, comprising:
         applying a first set of neighboring samples of a current block onto an ALWIP to obtain a prediction of a set of transform coefficients of a transform of a current block.       

     A method of above and/or below may use the equipment comprising at least one apparatus as above and/or below. 
     If the proposed predictor predicts transform coefficients, the transform coefficients not predicted may be inferred to be zero. Which transform coefficients are to be predicted may depend only on the given mode, not on the input (e.g., not on the neighboring blocks). Additionally, it might be fixed in advanced that for the given transform all high frequency components of the prediction signal starting at a certain point are inferred to be zero. 
     In examples, there may be defined a mapping which maps a mode into another mode for which the resampling has to be performed. 
     Examples above are mainly discussed for ALWIP modes, but they may be generalized to conventional modes and other kinds of modes. 
     Prediction from the Transform Domain 
     Some prediction modes of the present application might be configured to first apply a transform which has an energy compaction property on natural images (e.g. a Discrete Cosine Transform, DCT, or a Wavelet Transform) and to use only some of the resulting transform coefficients as an input for the affine linear prediction supported by the apparatus. The coefficients to be used might be either fixed in advanced (e.g., only low frequency coefficients) or might be derived from the transformed signal itself (e.g., only the frequency coefficients with the largest amplitude). 
     If it is fixed in advanced which frequency coefficients are to be used, then only a partial transform might be applied to the input signal, for example a Discrete Cosine Transform computing only low frequency coefficients or one or several stages of a Low-Pass-Filtering corresponding to a given Wavelet-Transform. 
     Transposing Proposed Prediction Modes 
     The example here discussed will be described in detail subsequently, with particular reference to  FIGS.  11   a    and  11   b.    
     For a given block  18  with N rows and M columns, an ALWIP mode already supported by the apparatus for that block and a given block with M rows and N columns, the apparatus may be configured to support a new prediction mode on the block with M rows and N columns by: First, mapping a template consisting of neighboring, already reconstructed samples for the block with M rows and N columns to a template that serves as an input for the affine-linear intra-prediction on the block with N rows and M columns. Second, applying the ALWIP mode on the block with N rows and M columns. Third, transposing the result of the latter prediction so that it becomes a prediction signal on the block with M rows and N columns. It is pointed out that M and N might be equal. 
     Here, to explain the first step further, if for example the template consisting of neighboring, already reconstructed samples for the block with M rows and N columns consists of k rows above the block and I columns left of the block and if the template that serves as an input for the affine-linear prediction on the block with N rows and M columns consists of I rows above the block and k columns left of the block, then the p-th row above the block with M rows and N columns might be mapped to the p-th column left of the block with N rows and M columns and the q-th column left of the block with M rows and N columns might be mapped to the q-th row above the block with N rows and M columns. 
     There is the possibility of performing mapping operations, e.g. from a mode which would be applicable to the M×N block to an associated mode which is applicable to the N×M block. 
     Examples above have mainly been referred to ALWIP modes, even though they may be also valid for conventional modes and/or other modes. 
     Mapping Between Mode-Indices 
     For a given block shape and for an ALWIP intra-prediction for that block shape which are part of the proposed apparatus and methods, there may be a mapping that maps each ALWIP mode to a conventional intra prediction mode (DC-, Planar- or Angular) which are present in the underlying codec (and vice versa, in examples). 
     This mapping might be used in the signalization scheme of the conventional intra-prediction modes which is present in the underlying codec. Namely, if at the decoder a list is generated, which performs a ranking among the conventional intra-prediction modes and if this list is used in their signalization and if the generation of the latter list is realized by a fixed rule using the conventional intra-prediction modes of surrounding, already reconstructed, blocks, then this rule is extended to also include surrounding, already reconstructed blocks which use one of the ALWIP modes proposed in the underlying apparatus by first applying the mapping to each of these modes and then treating them as conventional intra prediction modes in the generation of the list. 
     Moreover, this mapping might additionally be used as follows: if the luma-prediction signal is generated using one of the ALWIP modes for that block shape, the chroma prediction signal can be obtained by using the conventional intra prediction mode corresponding to the ALWIP via the mapping. 
     For a given block shape and given ALWIP mode for that block shape which are part of the proposed apparatus, there may be a mapping that maps each of the conventional intra-prediction modes that are present in the underlying codec to an ALWIP mode for that block-shape which is part of the proposed apparatus. 
     For a given first block shape and for given ALWIP intra-prediction modes for the first block shape which are part of the proposed apparatus and for a given second block shape and given ALWIP intra-prediction modes for the second block shape which are part of the proposed apparatus, there may be a mapping which maps each ALWIP mode for the first block shape to an ALWIP for the second block-shape. 
     This mapping may be realized as first applying the mapping described in above paragraph of the present section and then applying the mapping of the second paragraph of the present section to the result (or vice versa). The last two mappings just described might both be used to generate a ranking of all available ALWIP modes on a given block using the intra-prediction modes of neighboring blocks which might be either conventional intra prediction modes or ALWIP modes: One first applies the mapping to each of the neighboring intra prediction modes which gives a set of ALWIP modes corresponding to the shape of the given block. Then, by a predefined rule, one ranks all possible ALWIP modes; ALWIP modes that occur in the set corresponding to the surrounding blocks may be ranked differently than other ALWIP modes. 
     The latter ranking might be used in the signalization of the ALWIP mode by coding the ALWIP mode with different numbers of bins corresponding to that ranking. 
     Description of Aspects of Examples Regarding ALWIP Transformations 
       FIG.  2    shows the decoder  54  for decoding a picture from a data stream  12 . The decoder  54  may be configured to decode a predetermined block  18  of the picture. In particular, the predictor  44  may be configured for mapping a set of P neighboring samples neighboring the predetermined block  18  using a linear or affine linear transformation [e.g., ALWIP] onto a set of Q predicted values for samples of the predetermined block. 
     As shown in  FIG.  5   , a predetermined block  18  comprises Q values to be predicted (which, at the end of the operations, will be “predicted values”). If the block  18  has M rows and N columns, the values to be predicted amount to Q=M*N values. The Q values of the block  18  may be in the spatial domain (e.g., pixels) or in the transform domain (e.g., DCT, etc.). The Q values of the block  18  may be predicted on the basis of P values taken from the neighboring blocks  17   a - 17   c , which are adjacent to the block  18 . The P values of the neighboring blocks  17   a - 17   c  may be in the closest positions (e.g., adjacent) to the block  18 . The P values of the neighboring blocks  17   a - 17   c  have already been processed and predicted. The P values are indicated as values in portions  17 ′ a - 17 ′ c  (forming a so called “template”), to distinguish them from the blocks they are part of (in some examples,  17 ′ b  is not used). 
     As shown in  FIG.  6   , in order to perform the prediction, we may operate with a first vector  17 P with P entries (each entry being a particular position in the neighboring portions  17 ′ a - 17 ′ c ), a second vector  18 Q with Q entries (each entry being a particular position in the block  18 ), and a mapping matrix  17 M (each row being associated to a particular position in the block  18 , each column being associated to a particular position in the neighboring portions  17 ′ a - 17 ′ c ). The mapping matrix  17 M therefore performs the prediction of the P values of the neighboring portions  17 ′ a - 17 ′ c  (template) into values of the block  18  according to a predetermined mode. The entries in the mapping matrix  17 M are therefore weighting factors. The matrix  17 M (which may be associated to a conventional mode or to an ALWIP mode) may be pre-defined and stored in a storage unit (e.g., register, memory, etc.) of the decoder and/or encoder, or may be obtained on-the-fly. The matrix  17 M (and the associated mode, as well) is in general associated to a particular size. E.g., a size M×N is in general not the same of M 1 ×N 1  (with M≠M 1  and/or N≠N 1 ), and a mode associated to a size M×N is in general different from the mode associated to the size M 1 ×N 1 , and the matrix  17 M for the mode associated to a size M×N is in general different from the matrix  17 M for the mode associated to the size M 1 ×N 1 . For a mode associated to a size M×N, the matrix  17 M will have Q rows, where Q=M*N. For a mode associated to a size M 1 ×N 1 , the matrix  17 M will have Q 1  rows, where Q 1 =M 1 *N 1 . 
     In the art there are known several conventional modes, such as DC mode, planar mode and 65 directional prediction modes. There may be known, for example, 67 modes. See below for a discussion on the conventional modes. 
     However, it has been noted that it is also possible to make use of different modes (apart from the conventional ones). The different, additional modes that are here presented are here called linear or affine linear transformations. The linear or affine linear transformation (associated to the matrix  17 M) comprises P*Q weighting factors, among which at least ¼ P*Q weighting factors are non-zero weighting values, which comprise, for each of the Q predicted values, a series of P weighting factors relating to the respective predicted value. The series, when being arranged one below the other according to a raster scan order among the samples of the predetermined block  18 , form an envelope which is omnidirectionally non-linear. 
       FIG.  7    shows an example of a diagram  70  mapping the P positions of the neighboring values  17 ′ a - 17 ′ c  (template), the Q positions of the blocks  17 ′ a - 17 ′ c , and at the values of the P*Q weighting factors of the matrix  17 M. A plane  72  is the envelope of the series for a DC transformation (which is a plane for the DC transformation). The envelope is evidently planar and therefore is excluded by the definition of the linear or affine linear transformation (ALWIP). The planar mode and the 65 directional prediction modes would have different envelopes, which would however omnidirectionally linear. To the contrary, the envelope of the linear or affine transformation will not be omnidirectionally linear. It has been understood that such kind of transformation may be optimal, in some situations, for performing the prediction for the block  18 . It has been noted that it is advantageous that at least ¼ of the weighting factors are different from zero (i.e., at least the 25% of the P*Q weighting factors are different from 0). The weighting factors may be unrelated with each other according to any regular mapping rule. Hence, a matrix  17 M may be such that the values of its entries have no apparent recognizable relationship. 
     In examples, an ALWIP transformation is such that a mean of maxima of cross correlations between a first series of weighting factors relating to the respective predicted value, and a second series of weighting factors relating to predicted values other than the respective predicted value, or a reversed version of the latter series, whatever leads to a higher maximum, may be lower than a predetermined threshold (e.g., 0.2 or 0.3 or 0.35 or 0.1, e.g., a threshold in a range between 0.05 and 0.035). 
     The P neighboring samples ( 17 ′ a - 17 ′ c ) of blocks  17   a - 17   c  may be located along a one-dimensional path extending along a border (e.g.,  18   c ,  18   a ) of the predetermined block  18 . For each of the Q predicted values of the predetermined block  18 , the series of P weighting factors relating to the respective predicted value may be ordered in a manner traversing the one-dimensional path in a predetermined direction (e.g., from left to right, from top to down, etc.). 
     In examples, the ALWIP matrix  17 M may be non-diagonal or non-block diagonal. 
     An example of ALWIP matrix  17 M for predicting a 4×4 block  18  from 4 already predicted neighboring samples may be: 
     
       
         
           
               
             
               
                   
               
             
            
               
                 { 
               
               
                 { 37, 59, 77, 28}, { 32, 92, 85, 25}, { 31, 69, 100, 24}, { 33, 36, 106, 29}, 
               
               
                 { 24, 49, 104, 48}, { 24, 21, 94, 59}, { 29, 0, 80, 72}, { 35, 2, 66, 84}, 
               
               
                 { 32, 13, 35, 99}, { 39, 11, 34, 103}, { 45, 21, 34, 106}, { 51, 24, 40, 105}, 
               
               
                 { 50, 28, 43, 101}, { 56, 32, 49, 101}, { 61, 31, 53, 102}, { 61, 32, 54, 100} 
               
               
                 }. 
               
               
                   
               
            
           
         
       
     
     (Here, {37, 59, 77, 28} is the first row; {32, 92, 85, 25} is the second row; and {61, 32, 54, 100} is the 16 th  row of the matrix  17 M.) Matrix  17 M has dimension 16×4 and includes 64 weighting factors (as a consequence of 16*4=64). This is because matrix  17 M has dimension Q×P, where Q=M*N, which is the number of samples of the block  18  to be predicted (block  18  is a 4×4 block), and P is the number of samples of the already predicted samples (e.g.,  17 ′ a - 17 ′ c ). Here, M=4, N=4, Q=16 (as a consequence of M*N=4*4=16), P=4. The matrix is non-diagonal and non-block diagonal, and is not described by a particular rule. 
     As can be seen, less than ¼ of the weighting factors are 0 (in this case, one weighting factor out of sixty-four is zero). The envelope formed by these values, when arranged one below the other one according to a raster scan order, form an envelope which is omnidirectionally non-linear. 
     Even if the explanation above is directed to a decoder, the same may be performed at the encoder (e.g., encoder  14 ). 
     In some examples, for each block size (in the set of block sizes), the ALWIP transformations of intra-prediction modes within the second set  122  of intra-prediction modes for the respective block size are mutually different. In addition or in alternative, a cardinality of the second set  122  of intra-prediction modes for the block sizes in the set of block sizes may coincide, but the associated linear or affine linear transformations of intra-prediction modes within the second set of intra-prediction modes for different block sizes may be non-transferable onto each other by scaling. 
     In some examples the ALWIP transformations may be defined in such a way that they have “nothing to share” with conventional transformations (e.g., the ALWIP transformations may have “nothing” to share with the corresponding conventional transformations, even though they have been mapped via one of the mappings above). 
     In examples, ALWIP modes are used for luma components, but they may be avoided for chroma components. 
     Here below, reference is mainly made to:
         a first set  121  of conventional intra-prediction modes including a plurality of directional prediction modes and at least one of a DC mode and a planar mode (the set may have 67 modes, for example); and   a second  122  set of intra-prediction modes (e.g., linear or affine prediction modes, ALWIP, as discussed above).
 
Signaling, Mapping
       

     It is here explained how to reduce the size of a bitstream (e.g.,  12 ,  80 ) encoding a signaling the prediction mode to be chosen, for example, using a unary variable length code or another variable length code. 
     The choice may be made by the encoder which encodes, in the bitstream, a variable-length code (which may be unary) of the type “000 . . . 1”, wherein the “1” is positioned after a sequence of “0” s. (More in general, more frequent intra prediction modes are given a cheaper code, even if not necessarily unary.) The shortest field may therefore be “1” (which indicates a first prediction mode); the second shortest field may be “01” (which indicates a second prediction mode); etc. (a string with 66 “0”s and one “1” in the 66 th  position could indicate a last of 67 prediction modes, for example). As this code may be signaled for each block of a multitude of blocks to be predicted, it is in general advantageous that the field is short for each block (i.e., that the modes to be used are indicated by a short string, such as “1”, “01”, “001”, and so on), while avoiding fields with tens of “0”s. A strategy based on rankings among modes has therefore been developed. According to such a strategy, the length of the code depends monotonically on a rank of the intra-prediction mode in a list of intra-prediction mode, so as to recognize an index pointing at a particular prediction mode in the list. The list may be understood as a list of most probable modes and may be construed by rules which are common to the encoder and the decoder, even though the list is not directly signaled by the encoder to the decoder. 
       FIG.  8    shows a data (video) stream  80  (e.g.,  12 ) encoding an image (e.g.,  10  in  FIGS.  1 - 4   ). The portion of the data stream  80  may refer to the predetermined block  18  to be decoded. 
     The data stream  80  may comprise a first signalization  81  for assigning the block  18  to the first set  121  or second set  122  of intra-prediction modes. The signalization  81  may need one single bit, in some examples. 
     A second signalization  82  (variable length code) in the data stream  80  may include a unary variable-length code of the type “000 . . . 1”, as discussed above, or another variable-length code, which may assign cheaper codes (e.g., codes requiring a smaller number of bits) to more frequent intra prediction modes. 
     When the decoder  54  reads the first signalization  81 , it understands that the block  18  is to be predicted with either an intra-prediction mode of the first set or an intra-prediction mode of the second set (i.e., though the flag  81 , the block  18  is either assigned to the first set  121  of conventional modes or the second set  122  of ALWIP modes). 
     Then, in some examples the decoder  54  may sort the assigned set of prediction modes (as indicated in the first signalization  81 ) according to intra-prediction modes (e.g., previously used for neighboring blocks  17   a - 17   c ). A list  90  of intra-prediction modes may therefore be obtained (“list of most probable modes”). The list  90  may be stored in a register in the decoder  54  and the encoder  14 . The list  90  may therefore provide a particular order which is here indicated with a first position  91 , a second position  92 , a third position  93 , a fourth position  94 , and a fifth position  95 . Other positions may of course be provided, e.g., to cover all the modes of the assigned set. However, in some examples, the list  90  does not need to have as many positions as the number of modes in the set (either conventional modes or ALWIP modes), but could be smaller. In examples, it may be that the list  90  comprises less than 10 positions, e.g., a number of positions which is between 3 and 7, e.g., 5). In the list  90 , the first position  91  is here taken by the prediction mode “23”, while the second position  92  is taken by the prediction mode “15” etc. (The numbering of the modes may be stored in a look-up table, LUT, for example). 
     It is to be noted that, in examples, the assignment to the particular positions are not signaled in the data stream  80  ( 12 ), but may be determined by the decoder on the basis of the previously performed predictions on blocks  17   a - 17   c . In some examples, the previously most-used intra prediction modes (or, in any case, intra prediction modes which are statistically more frequent) may gain the highest positions in the list  90  (highest positions may be understood as highest-ranking positions). In this case, the mode “23” is the previously most-used prediction mode and therefore is awarded of the first position  91 . It is also to be noted that the same sorting is performed at the encoder. The encoder will obtain a copy of the list  90  (on the basis of the same historical data on the most-used prediction modes). Therefore, the encoder and the decoder share the same list even without the necessity of signaling it in the data stream  80 . Other techniques are possible. 
     It has been understood that, by assigning the shortest (cheaper) codes (e.g., “1”, “01”, “001” . . . ) in the data stream  80  (e.g.,  12 ) to the highest positions ( 91 ,  92 ,  93  . . . ) in the list  90 , the size of the data stream  80  can be reduced. This conclusion has been possible on the basis of the consideration that the most-used prediction modes (e.g., “23”, “15”, “18” . . . ) are also the most probable prediction modes for the current block  18 . (In alternative, it is the most statistically probable modes which are awarded the highest positions (highest ranks) in the list  90 .) Therefore, by assigning short codes to the most probable prediction modes, a reduction of the size of the data stream  80  is obtained. 
     It is noted that the second signalization  82  is not necessarily encoded as unary code. For example, a truncated binary code may be used. An example of truncated binary code is provided in the following table: 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 Index 
                 Code in field 82 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                  91 
                 0 
               
               
                   
                  92 
                 1 
               
               
                   
                  93 
                 10 
               
               
                   
                  94 
                 11 
               
               
                   
                  95 
                 100 
               
               
                   
                  96 
                 101 
               
               
                   
                  97 
                 1100 
               
               
                   
                  98 
                 1101 
               
               
                   
                  99 
                 1110 
               
               
                   
                 100 
                 1111 
               
               
                   
               
            
           
         
       
     
     The index  0  is associated to the highest index  91  (which is in turn associated to the most probable mode), the index  1  is associated to the second-highest index (which is in turn associated to the second most probable mode), the index  10  is associated to the third-highest (which is in turn associated to the third most probable mode), and so on. As can be seen the third most probable mode is associated to an index which is less cheap than the indexes associate dot the first and second most probable modes (as index  10  for the third most probable mode needs two bits in the bitstream  80 , while the indexes  0  and  1  for the first and second most probable modes only need one bit each for the encoding). 
     The second signalization  82  may therefore contain encoded an index which points to the particular position. E.g., if the second signalization  82  contains “1”, the first position  91  will be pointed to, hence indicating that the mode “23” is to be used. If (with reduced probability) the second signalization  82  contains “01”, the second position  92  will be pointed to, hence indicating that the mode “15” is to be used, and so on. 
     Accordingly, it is possible to predict for the encoder and the decoder the predetermined block  18  to be used using an intra prediction mode onto which the index points. 
     There may arise some issues in some cases. An example is when the predetermined block  18  is to be predicted using a conventional mode (i.e., the first signalization  81  indicates that a conventional mode is to be used), but one of the neighboring blocks  17   a - 17   c  has been previously predicted using an ALWIP mode. This would imply that one of the indices  91 - 95  of the list  90  should indicate an ALWIP mode, which cannot be used (as the first signalization  81  involves a conventional mode). Hence, a useless indication would be present in the list  90 . 
     However, it has been understood that it is possible to map some ALWIP modes into conventional modes. Hence, if a particular ALWIP mode ALWIP 1  had been used, the mapping will permit to derive a particular conventional mode CONV 1  (mapping ALWIP 1  according to the mapping). Hence, when an ALWIP mode is used for a previous block  17   a ,  17   b , or  17   c , subsequently one of the indexes  91 - 95  will indicate a mapped conventional mode associated to the previously used ALWIP mode. Accordingly, no index  91 - 95  of the list  90  will be wasted indicating a non-usable mode. The mapping may be pre-defined and known by both the encoder and the decoder. 
     The same may apply by mapping a conventional mode into an ALWIP mode. It is to be noted, however, that in some examples the list  90  of the most probable mode is only used for a particular set (e.g., the first set  121  of the conventional modes), while no such a list is used for other sets (or the list of most probable modes may be pre-defined, and fixed): this brings, in such examples, to the unnecessity of some mappings. (For example, in some cases the list of most probable ALWIP modes may be pre-defined based on pre-assumed probabilities, and is never changed on-the-fly: hence, no mapping is provided in these cases). 
     The mappings may also refer to block sizes: different mappings may be used for different sizes. Hence, there may be stored multiple mappings for different sizes (i.e., a mapping for a M×N size may be different from a mapping for M 1 ×N 1  size). 
     It is possible to define mappings from a first size to a second size. This may be, for example, when the neighboring, previously predicted block  17   a ,  17   b , or  17   c  has a size which is different from the block  18  to be predicted. 
     It could also be possible to map ALWIP modes but associated to different sizes. 
     A discussion on the mappings is here provided. 
     If the assigned set is the second set  122  of intra-prediction modes (ALWIP), e.g. in sorting the assigned set, there may be used a first mapping which maps each intra-prediction mode of the first set of prediction modes onto a representative one in the second set of intra-prediction modes. If the assigned set is the second set of intra-prediction modes, in sorting the assigned set, there will be used a second mapping which maps each intra-prediction mode of the second set of prediction modes onto a representative one in the first set of intra-prediction modes. 
     Hereinafter, at least one of the following mappings may be used:
         First mapping ( 101   a ,  FIG.  10   a   ′): conventional to ALWIP (same size);   Second mapping ( 102   a  in  FIG.  10   a   ′,  102   b  in  FIG.  10   b   ): ALWIP to conventional (same size);   Third mapping ( 103 ,  FIG.  10   c   ): conventional to ALWIP (from a size of the neighboring block predicted through a conventional mode to a different size of the block  18  to be predicted through an ALWIP mode);   Fourth mapping ( 104 ,  FIG.  10   d   ): ALWIP to conventional (from a size of the neighboring block predicted through an ALWIP mode to a different size of the block  18  to be predicted through a conventional mode);   Fifth mapping ( 105 ,  FIG.  10   a   ′″): from ALWIP to ALWIP (different size);   Generalized fifth mapping ( 106 ,  FIG.  10   e   ): from one size to another size (general example)       

     A mode detailed discussion is here provided.  FIG.  10   a    is subdivided into  FIGS.  10   a   ′,  10   a ″,  10   a′″.    
       FIG.  10   a   ′ shows an example of a first mapping  101   a , in which different conventional modes (CONV 1 , CONV 2 , CONV 3 ) are mapped, through different mappings, into different ALWIP modes (ALWIP  1 , ALWIP 2 , ALWIP 3 ). In examples, the different conventional modes and the different ALWIP modes have the same size. In the examples in which, for ALWIP, the list  90  is not updated on the fly (but the indexes are provided based on pre-defined probabilities), this mapping is not used. 
       FIG.  10   a   ″ shows an example of a second mapping  102   a , in which different ALWIP modes (ALWIP  1 , ALWIP 2 , ALWIP 3 ) of the second set  122  are mapped into different conventional modes (CONV 1 , CONV 2 , CONV 3 ) of the first set  121 . In examples, the different conventional modes and the different ALWIP modes have the same size. This second mapping may be used when the list  90  of most probable modes is updated on-the-fly at least for conventional modes (hence, the list  90  can be called “list  90  of most probable conventional modes”). Hence, if a previous block  17   a ,  17   b , or  17   c  has been predicted using 
     ALWIP 2 , the list  90  will indicate the conventional mode CONV 1  in one of its indexes (i.e., CONV 1  will be one of the most probable conventional modes, even if CONV 1  had not been already used, by virtue of ALWIP 1  having been used, and by virtue of the second mapping  102   a  mapping ALWIP 2  onto CONV 1 ). 
       FIG.  10   c    shows an example of a third mapping  103 , in which conventional modes of the first set  121  (size  152 ) are mapped into ALWIP modes of the second set  122  (size  151 ). In the examples in which, for ALWIP, the list  90  is not updated on the fly (but the indexes are provided based on pre-defined probabilities), this mapping is not used. 
       FIG.  10   d    shows an example of a fourth mapping  104 , in which ALWIP modes of the second set  122  (size  151 ) are mapped into conventional modes of the first set  121  (size  152 ). In the examples in which, for ALWIP modes, the list  90  is not updated on the fly (but the indexes are provided based on pre-defined probabilities), this fourth mapping  104  is not used. 
       FIG.  10   a   ′″ shows an example of a fifth mapping  105 , in which different ALWIP modes (ALWIP 11 , ALWIP 12 , ALWIP 13 ) of the same size (size 1  or  151 ) are mapped, through different mappings ( 105   1 ,  105   n ), into different ALWIP modes (ALWIP 11 ′, ALWIP 12 ′, ALWIP 13 ′) of different sizes. Other ALWIP modes (ALWIPn 1 , ALWIPn 2 , ALWIPn 3 ) of the same size (size n or  15   n ) may be mapped into different ALWIP modes (ALWIPn 1 ′, ALWIPn 2 ′, ALWIPn 3 ′) of different sizes. Hence, there arises the possibility of mapping any ALWIP mode into a different other ALWIP mode. 
       FIG.  10   e    shows mapping  106 , which is a more general example than the fifth mapping  105 . Here, different modes used for a size  151  are mapped onto modes for a different size  152 . This mapping does not only maps ALWIP modes into ALWIP modes, but also conventional modes onto conventional modes, conventional modes onto ALWIP modes, and ALWIP modes onto conventional modes. 
     A particular case of the second mapping  102   a  is here discussed with reference to the second mapping  102   b  of  FIG.  10   b   . In some examples, a plurality of (or all) ALWIP modes of the same size (among the set of sizes) may be mapped onto one single conventional mode. Here, a first set  121  of conventional modes  131  is shown. Here, for the first set  121  of conventional modes, only one mode  131  is represented, each of these modes being associated to a particular size (e.g., CONV 11  being one particular conventional mode  131  for the size  1 ; CONV 21  being one particular conventional mode  131  for the size  2 ; CONV 1  being one particular conventional mode  131  for the size n; and so on). The first set  121  may include other conventional modes  131  which are here not shown. However, the conventional modes  131  (CONV 11 , CONV 12 , CONV 13 ) which are here shown may be, for example, of the same type (e.g., all planar modes). A second set  122  of ALWIP modes is also shown. The second set  122  includes, for each size (e.g., size 1 , size 2 , . . . , size n), a plurality of modes (size 1 : ALWIP 11 , ALWIP 12 , ALWIP 13 ; size 2 : ALWIP 21 , ALWIP 22 , ALWIP 23  size n: ALWIPn 1 , ALWIPn 2 , ALWIPn 3 ). A second mapping  102   b  may be defined. For example, a plurality of (or all) the ALWIP modes of the same size (size 1 ) (i.e., ALWIP 11 , ALWIP 12 , ALWIP 13 ) may be mapped to the same conventional mode CONV 11  (which may have the same size of ALWIP 11 , ALWIP 12 , ALWIP 13 ). Hence, even though there are other (non-shown) conventional modes  131  with same size (size 1 ) in the first set  121 , the plurality of (or all) the ALWIP modes is mapped to the same conventional mode conv 11 . The same may apply to the ALWIP modes of size  2  (ALWIP 21 , ALWIP 22 , ALWIP 23 ), which are all mapped to the same conventional mode CONV 21 . The same may apply to the ALWIP modes of size n (ALWIPn 1 , ALWIPn 2 , ALWIPn 3 ), which are all mapped to the same conventional mode convn 1 . In some examples, the conventional mappings CONV 11 , CONV 21 , CONV 2 , to which the plurality of ALWIP modes is mapped, may all be planar modes. Accordingly, multiple different ALWIP modes may be mapped onto one single conventional mode. (In specular examples, different ALWIP modes may be mapped into multiple conventional modes.) 
     In some examples, at least one of the following techniques may be implemented:
         if one of the neighboring blocks ( 17   a - 17   c ) is of the same block size within the set of block sizes as the predetermined block ( 18 ), but assigned to a different one of the first and second sets ( 121 ,  122 ) of intra-prediction modes, use the first or second mapping ( 101   a ,  101   b ,  102   b );   if one of the neighboring blocks ( 17   a - 17   c ) is of a different block size within the set of block sizes from the predetermined block ( 18 ), use,
           if the assigned set for the predetermined block ( 18 ) is the second set ( 122 ) for the predetermined block&#39;s block size while an assigned set for the one neighboring block ( 17   a - 17   c ) is the first set ( 121 ) for the one neighboring block&#39;s block size, use the third mapping ( 103 ) which maps each intra-prediction mode of the first set ( 121 ) of prediction modes for the one neighboring block&#39;s block size, onto a representative one in the second set ( 122 ) of intra-prediction modes for the predetermined block&#39;s block size, and/or,   if the assigned set for the predetermined block ( 18 ) is the first set ( 121 ) for the predetermined block&#39;s block size while an assigned set for the one neighboring block ( 17   a - 17   c ) is the second set ( 122 ) for the one neighboring block&#39;s block size, use the fourth mapping ( 104 ) which maps each intra-prediction mode of the second set ( 122 ) of prediction modes for the one neighboring block&#39;s block size, onto a representative one in the first set ( 121 ) of intra-prediction modes for the predetermined block&#39;s block size, mapping and/or   
           if one of the neighboring blocks ( 17   a - 17   c ) is of the different block size within the set of block sizes as the predetermined block ( 18 ), if the assigned set for the predetermined block ( 18 ) is the second set ( 122 ) for the predetermined block&#39;s block size and an assigned set for the one neighboring block ( 17   a - 17   c ) is the second set ( 122 ) for the one neighboring block&#39;s block size:
           use the fifth mapping ( 105 ) which maps each intra-prediction mode of the second set ( 122 ) of prediction modes for the one neighboring block&#39;s block size, onto a representative one in the second set ( 122 ) of intra-prediction modes for the predetermined block&#39;s block size.   
               

     The mappings from conventional to ALWIP (e.g.,  102   a ,  102   b ) may be used for chroma components when ALWIP modes have been used for luma components. 
     As explained above, in some examples the list  90  is static. This may be, for example, when the flag  81  involves the use of ALWIP modes, in these cases, in some examples, there is not a list  90  updated on-the-fly, but a list with pre-defined relationships. 
     In examples above, reference has been often made to a list  90  pointing at five modes through five indexes  91 - 95 , but different (larger or smaller) numbers of indexes may be defined. 
     In examples, the first signalization  81  may involve one single bit (e.g., signaling a choice between “ALWIP mode” and “conventional mode”). In examples, the second signalization  82  may use a variable length: for example, cheaper codes (e.g., having narrower lengths) may be associated to statistically most frequent modes. In some cases, code length depends (e.g., monotonically) on the rank of the intra-prediction mode the index points to: higher ranks may be associated to most frequent indexes (and most frequent modes, too). An example may be a unary code (see above), even if other codes may be used. 
     Transpositions 
     Reference is now made to  FIGS.  11   a ,  11   b , and  11   c   , referring to the above discussed “transposing proposed prediction modes”. Here, a predetermined block  18  of the size M×N (with M≠N) or N×M (with M≠N) is to be predicted from the previously-predicted neighboring blocks  17   a ,  17   b ,  17   c , and in particular from the series of the P neighboring samples  17 ′ a - 17 ′ c , which form a template  170 . (It is here imagined that the block  17   b  shown in  FIG.  5    is not used, but it could be used in some examples.) 
     We assume that the decoder  56  or the encoder  14  has a particular ALWIP mode (here indicated as ALWIP 1 ) which is suitable for the size N×M, but not for the size M×N. Said in other terms, there is stored an N×M ALWIP matrix  17 M is, but there is not a M×N ALWIP matrix  17 M. (It could be imagined that it would be in principle be advantageous to have, stored, another M×N matrix for ALWIP mode. However, in order to reduce the storage and/or the signaling, it may be advantageous to reduce the amount of ALWIP modes stored in the encoder and/or decoder.) 
     In some cases, the first signalization  81  in the stream  80  ( 12 ) may indicate that an ALWIP mode is to be used for the predetermined block  18 . The second signalization  82  may have, encoded, an index which is associated to ALWIP 1  (or, in any case, to indicate ALWIP 1 ). Hence, different operations may be performed according to the orientation of the block  18 .
         If, like in  FIG.  11   a   , the predetermined block  18  to be predicted has the size M×N (which corresponds to the size of ALWIP 1 ), then mode ALWIP 1  is applied ( 140 ) to the P samples of the template  170 , to predict the P samples of the block  18 .   If, like in  FIG.  11   b   , the predetermined block  18  to be predicted has the size M×N (which is the opposite of the size of the size of ALWIP 1  as stored), then it is not possible to simply apply ALWIP 1 , as ALWIP 1  has a size N×M different from the size M×N of the predetermined block  18  (it is hypothesized that there is not stored a N×M matrix  17 M,). However, it has been understood that it is possible to adopt a technique according to which the encoder  14  or the decoder  54  performs the following steps:
           1) reversing ( 141 ) the series of the template  170  (oriented according to the direction R 170 ) to obtain a reversed template  170  (e.g., oriented according to the direction R 170 T);   2) applying ( 142 ) ALWIP 1  to the reversed version  170 T of the template  170 , so as to obtain a predicted block  18 T with size N×M (compliant with ALWIP 1 ); and   3) transposing ( 144 ) the predicted block  18 T, to obtain the predetermined block  18 .   
               

     Notably, it is not necessary that a signaling is provided in the stream  12  ( 80 ) whether the M×N ALWIP mode or N×M ALWIP mode is to be used, and is not necessary to signal that a transposition is to be made. It is simply possible to use the fifth mapping  105  of  FIG.  10   a   ′″. In fact, in order to reconstruct block  18 :
         1) The second signalization  82  (either directly, or via the indexes  91 - 95  of the list  90 ) may signal that a particular ALWIP mode (e.g., ALWIP 1 ) is to be used for an M×N block  18 ;   2) However, at the decoder there is not an M×N matrix stored for ALWIP 1  (ALWIP 1  may be considered as being part of a subset  120 N of non-stored ALWIP modes);   3) Notwithstanding, at the decoder there stored an N×M ALWIP mode (which may be considered as being part of a subset  120 S of stored ALWIP modes);   4) The mapping  105  maps the non-stored M×N ALWIP 1  onto the stored N×M ALWIP mode;   5) The procedure of  FIG.  11   b    may be performed, hence arriving at the reconstruction of the block  18 .       

     The example above is proposed for a rectangular block M×N with M≠N. However, an analogous procedure may be performed for a square (quadratic) block M×M. It has been noted in fact, that in some cases there arises the possibility of simply applying a reversed version of the template  170 , performing the prediction using a stored transformation, and finally transposing the obtained block  180 T, exactly as in  FIG.  11   b    (but with M=N). As shown in  FIG.  11   d   , a set  120 Q of modes (ALWIP and/or conventional) may comprise the following subsets:
         A first subset  120 QS of stored modes for quadratic blocks (for these modes, the matrix  17 M is stored); and   A second subset  120 QN of non-stored modes for quadratic blocks, but for which it is possible to perform the prediction by using the method of  FIG.  11   b    (with M=N).       

     Hence, if (CASE 1), an index  91 - 95  or a second signalization directly indicates a mode in the first subset  120 QS of stored modes, then the mode is directly invoked (and the procedure of  FIG.  11   a    is performed, with M=N). 
     Otherwise, if (CASE 2), an index  91 - 95  or a second signalization directly indicates a mode in the second subset  120 QN of non-stored modes, then a mode from the first subset  120 QS is invoked after having mapped from the mode of the subset  120 QN. 
     Examples discussed above and below may be in the spatial domain and/or in the transform domain. 
     Example in the Transform Domain 
       FIG.  12    shows the prediction of a spatial-domain block  18  (which may be one of the predetermined blocks  18  as above, e.g., as in  FIG.  5   ) from previously predicted neighboring blocks  17   c  and  17   a . The prediction is performed here in the transform domain (e.g., after having applied a transformation such as fast Fourier transform, FFT, and/or discrete cosine transform, DCT, wavelet, etc.). 
       FIG.  12   ′ shows the predetermined block  18  to be predicted. Q values of the block  18  are to be predicted from first and second sets (e.g., proper subsets)  17 ′ c  and  17 ′ a  of the neighboring blocks  17   c  and  17   a  (the first and second sets  17 ′ c  and  17 ′ a  may represent lines or stripes or arrays in proximity, e.g. adjacent, to the sides  18   c  and  18   a  of the block  18  to be predicted, and may include already predicted samples). The values of the first and second sets  17 ′ c  and  17 ′ a  may be chosen independently of the sizes of the neighboring blocks  17   c  and  17   a , respectively: whatever the dimensions of the neighboring blocks  17   c  and  17   a , the dimensions of the first and second sets  17 ′ c  and  17 ′ a  are based on the dimensions of the block  18 . The values of the first and second sets  17 ′ c  and  17 ′ a  (template) may be chosen independently of the sizes of the blocks  17   c  and  17   a . In examples, the first and second sets  17 ′ c ,  17 ′ a  may be located along a one-dimensional path alongside the first and second sides  18   c ,  18   a , respectively. As discussed above, it is possible to perform a subsampling, e.g., by only taking some particular transform coefficients. 
     A transform  160  (e.g., FFT, DCT, wavelet, etc.) may be applied to at least some of the samples of the first and second sets  17 ′ c  and  17 ′ a . The first and second sets of transform coefficients  17 ′cT,  17 ′aT (template in the transform domain) may represent one-dimensional transforms of the samples of the first and second sets  17 ′ c ,  17 ′ a , the latter being located along one-dimensional path. It is not necessary to have the whole transform of the neighboring blocks  17   c  and  17   a , but only a low-frequency portion (or, in any case, a reduced portion). Advantageously, it does not matter if the sizes of the first and second sets  17 ′ c  and  17 ′ a  do not match the sizes of the sides  18   c  and  18   a  of the block  18 : the length of the sets  17 ′ c  and  17 ′ a  may be longer or shorter than the length of the sides  18   c  and  18   a.    
       FIG.  12   ″ shows that the first and second sets  17 ′ c  and  17 ′ a  (formed by “transform coefficients”) are now in the transform domain and are therefore indicated with  17 ′cT and  17 ′aT, respectively. 
     An ALWIP intra prediction transformation  162  is applied to the transform coefficients of the sets  17 ′cT and  17 ′aT. In  FIG.  12   ′″, therefore, a prediction block  18 T of the block  18  in the transform domain is therefore obtained. The ALWIP intra prediction transformation  162  may be according to an intra prediction mode as signaled in signalization(s)  81  and/or  82 . Notably, there arises the possibility that the prediction version  18 T in the transform domain of the block  18  has too few transform coefficients: in that case, it is simply possible to perform a zero-padding operation before the inverse transformation  164 : the remaining transform coefficients (e.g., the higher frequency bins) may be set at 0. Accordingly, after the inverse transformation  164 , the entire set of values of the block  18  may be obtained. Hence, the transform-domain prediction block  18 T may be smaller than the spatial-domain predicted block  18 . The transform-domain prediction block  18 T may also be greater than the predicted block  18 . In that case, a low pass filter may be subsequently applied. 
     An inverse FFT, IFFT, or inverse DCT, IDCT, or another inverse transformation  164  is applied to the prediction block  18 T, to obtain the predicted block  18  in the spatial domain in  FIG.  12   ″″. 
     In some examples, it is possible to yield a predictor of the predetermined block  18  in spatial domain. 
     Conventional Intra Prediction Modes 
     The following is a discussion on convectional intra prediction modes, at least some of which can be included in the first set  121  of conventional intra prediction modes (e.g., conv 1 , conv 2 , etc.). 
     The conventional intra prediction modes can be represented by matrix-vector multiplication and filtering operations applied to the input vector resp. the output vector. However, we point out that the matrices used in the latter computations of matrix vector products have a very special structure as we sail explain now. 
     To set up notation, we assume that an M×N block (M rows, N columns) is given on which an intra-prediction signal (in the luma component) is to be computed by a conventional intra prediction mode. The reference samples, which serve as an input of the prediction are comprised of already reconstructed samples. Typically, the reference samples may consist of a line of N+q samples above the block (where some samples above right of the block may not be available directly but might be generated by a fixed padding operation) and of M+p samples left of the block (where some samples below left of the block may not be available directly but might be generated by a fixed padding operation). 
     For the conventional intra prediction modes, the reference samples are regarded as a vector ref of size M+p+N+q. The first M+p entries of that vector consist of the reference samples left of the block and the last N+p entries of that vector consist of the samples above the block. 
     We first describe the case that the conventional intra prediction mode is a directional intra prediction mode, also called angular intra prediction mode. 
     Here, in a first step, an interpolation filtering operation is applied to the reference samples ref. The latter operation generates sample values on non-integral sample positions lying between the true sample positions in a fixed resolution. Thus, for a fixed integer k and each i∈{1, . . . , M+p+N+q−1}, k sample values are generated whose sample position lies between the i-th and the (i+1)-th entry of ref. The interpolation filtering operation may optionally be preceded or succeeded by a smoothing filtering operation. The overall result of the filter operations can again be regarded as a vector of size (M+p+N+q)*(k+1)−k which shall be denoted as ref fltr . It is pointed out that for some directional modes, for example the horizontal or the vertical intra prediction mode, no interpolation needs to be carried out, i.e. the number k may be equal to zero. 
     In a second step, for a fixed matrix A which corresponds to the conventional intra prediction mode and which has M*N rows and (M+p+N+q)*(k+1)−k columns, the prediction signal pred is computed as the matrix vector product
 
pred= A ·ref fltr ,
 
where · the denotes matrix-vector multiplication. Here, each row of the matrix A has only one non-zero entry which consist of a 1. In other words, each predicted sample value is exactly one value of ref fltr .
 
     In a final step, a second filtering operation might be applied to a signal which is the extension of pred by the already reconstructed samples left of the block resp. above the block to yield the overall directional intra-prediction signal. 
     Next, we describe the case that the conventional intra prediction mode is the planar mode. Here, only a smoothing and no interpolation operation might be applied to the reference samples to yield the vector ref fltr . If the (unfiltered) planar prediction signal pred planar  is computed by a matrix vector product
 
pred planar   =A   planar ·ref fltr ,
 
then the matrix A planar  has the property that each row of A planar  only consists of 4 non-zero entries. In other words, each predicted sample value is computed as a linear combination of 4 reference sample values. The column position of the 4 non-zero entries of a fixed row of A planar  are the position in ref fltr  corresponding to the reference sample left of the block that lies in the same row as the sample to be predicted, to the reference sample above of the block that lies in the same column as the sample to be predicted as well as the reference sample that lies in the row above the block and is the first sample in that row that lies strictly right of the block as well as the reference sample that lies in the column left of the block and is the first sample in that column that lies strictly below the block.
 
     In a final step, a second filtering operation might be applied to a signal which is the extension of pred planar  by the already reconstructed samples left of the block resp. above the block to yield the overall planar intra-prediction signal. 
     We finally describe the case that the conventional intra prediction mode is the DC mode. Here, if the (unfiltered) DC-prediction signal pred DC  is computed by a matrix vector product
 
pred DC   =A   DC ·ref fltr ,
 
then the matrix A DC  has the property that all rows of A DC  are equal. In a final step, a second filtering operation might be applied to a signal which is the extension of pred DC  by the already reconstructed samples left of the block resp. above the block to yield the overall DC intra-prediction signal.
 
     It is pointed out that the matrices used in the ALWIP intra prediction of the present application are not a priori constrained to one of the aforementioned patterns of the matrices corresponding to the directional-resp. the DC-resp. the planar-mode. Rather, they are the result of an offline data-driven training approach that takes into account for example the possibilty of splitting blocks into various shapes, a loss function modeling the loss (rate or rate-distortion) of a typical video encoder, the signalization costs needed to signal a mode as well as various other features known in the art. 
     Downsampling/Upsampling, Transform Domain for ALWIP 
     Reference is now made to  FIG.  13   . As explained above, in some cases, an encoder or decoder may perform transformations between predictors of different block sizes, e.g. by downsampling and/or upsampling. 
     As explained above, the “second template  1160 ” (in the spatial domain) may refer to a group of Q neighboring samples (above identified as  17 ′ a ,  17 ′ b ,  17 ′ c ) used for performing the intra prediction, but for which an ALWIP mode is not at disposal of the encoder or decoder. Basically, the “second template  1160 ” is formed by samples of  17 ′ a ,  17 ′ b ,  17 ′ c  which are used for the ALWIP prediction. 
     The discussion below is valid for both the ALWIP transformations and the conventional transformations, but is here mainly intended for ALWIP transformations. 
       FIG.  13    shows a current predetermined spatial-domain block B 1  (size M 1 ×N 1 ), which may be one block  18  in the examples above. The block  18  is to be predicted through an ALWIP transformation (e.g., one of the above). However, at the encoder or decoder there is at disposal an ALWIP transformation for a different size M×N (with M≠M 1  and/or N≠N 1 ). 
     It is noted that the second template  1160  (formed by samples  17 ′ a ,  17 ′ b ,  17 ′ c ) is already reconstructed (predicted). 
     If there is stored no ALWIP mode for reconstructing block  18  (B 1 ) by virtue of the dimensions of block  18  (B 1 ), in case an ALWIP transformation is at disposal for a block (B) with different dimensions M×N, the following procedure may be implemented. Notably, the ALWIP transformation for the block B of size M×N would need a template (here referred to as “first template  1161 ”) with different size than the already obtained second template  1160 . Hereinafter a technique which overcomes this impairment is discussed. 
     A transformation operation (here indicated as D) may, for example, be applied to the second template  1160 . The transformation D may provide an element  1136 , which is formed of a transformed (resampled) first template  1161  and a block  1138  (B) of size M×N to be predicted. 
     For example, the M 1 ×N 1  block B 1  ( 18 ) (with unknown coefficients) may be theoretically transformed into an M×N block B ( 138 ) (which, at this point, has also unknown coefficients). As the coefficients of block B ( 138 ) are unknown: a transformation into the transform domain is not necessary. 
     Analogously, the transformation D transforms the template  1160  (size M×N) into a different template  1161  (size M 1 ×N 1 ) with different dimensions. 
     In some cases, the transformation operation D may be, where M 1 &gt;M and N 1 &gt;N (and in particular where M is a multiple of M 1  and N is a multiple of N 1 ), a downsampling operation. For example, in case of M 1 =2*M and N 1 =2*N, the transformation operation D may simply be based on hiding some bins in a chess-like fashion. 
     At this point, the block B is predicted in M×N through an ALWIP transformation discussed above. The ALWIP transformation (associated to the size M×N) is contained at the encoder or decoder. At passage  1138   a , apparatus  14  or  54  may now use (e.g., at the predictor  44 ,  44 ′) the ALWIP transformation natively defined for an M×N block. By applying the passage discussed above, the prediction is obtained for block B of size M×N. 
     The prediction in block B ( 1138 ) is obtained for size M×N, while the image to be reconstructed shall have size M 1 ×N 1 . It is simply possible to perform a transformation  1140  (U) which transports the block B ( 1138 ) from size M×N into a block  18  of size M 1 ×N 1 . This transformation  1140  (U) may be, for example, a bilinear interpolation or an upsampling operation. This transformation  1140  (U) may be may be performed by introducing coefficients in the M 1 ×N 1  block, besides the coefficients in the M×N block  138 . For example, in case of M 1 =2*M and N 1 =2*N, it is simply possible to perform an interpolation (e.g., bilinear interpolation), so as to approximate (“guess”) the coefficients of that had been discarded by the transformation D. An M 1 ×N 1  prediction is therefore obtained as element block  18 , and may be used for displaying the block image as part of the image  10 . 
     In examples, it is possible to perform mappings from a mode which would be used for the block  18  (B 1 ) to the mode  1138   a.    
     Further Embodiments and Examples 
     Generally, examples may be implemented as a computer program product with program instructions, the program instructions being operative for performing one of the methods when the computer program product runs on a computer. The program instructions may for example be stored on a machine readable medium. 
     Other examples comprise the computer program for performing one of the methods described herein, stored on a machine-readable carrier. 
     In other words, an example of method is, therefore, a computer program having a program-instructions for performing one of the methods described herein, when the computer program runs on a computer. 
     A further example of the methods is, therefore, a data carrier medium (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. The data carrier medium, the digital storage medium or the recorded medium are tangible and/or non-transitionary, rather than signals which are intangible and transitory. 
     A further example of the method is, therefore, a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals may for example be transferred via a data communication connection, for example via the Internet. 
     A further example comprises a processing means, for example a computer, or a programmable logic device performing one of the methods described herein. 
     A further example comprises a computer having installed thereon the computer program for performing one of the methods described herein. 
     A further example comprises an apparatus or a system transferring (for example, electronically or optically) a computer program for performing one of the methods described herein to a receiver. The receiver may, for example, be a computer, a mobile device, a memory device or the like. The apparatus or system may, for example, comprise a file server for transferring the computer program to the receiver. 
     In some examples, a programmable logic device (for example, a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some examples, a field programmable gate array may cooperate with a microprocessor in order to perform one of the methods described herein. Generally, the methods may be performed by any appropriate hardware apparatus. 
     Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals even if occurring in different figures. 
     While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations and equivalents as fall within the true spirit and scope of the present invention.