High efficiency encoding and/or decoding apparatus

Abstract: A high efficiency encoding device for compressing the input information by temporal and/or spatial sampling is disclosed. The device transmits the input information supplied at an input terminal 10 to a thinning sub-sampling unit 11 and to a normal equation generating unit 12a in a model-associated coefficient calculating unit 12. The transmission information is supplied from the thinning sub-sampling unit 11 to an output terminal 13 and to the normal equation generating unit 12a. The normal equation generating unit 12a formulates normal equations by the least square method based on a linear first-order combination model and outputs the coefficients to a coefficient calculating unit 12b. The coefficient calculating unit 12b solves the normal equations to find most probable values for the unknown coefficients to output the calculated most probable values to an output terminal 14.

Description: This invention relates to a high efficiency encoding apparatus for compressing the input information by space-time sampling for transmitting the compressed information, and a high efficiency decoding apparatus for decoding the compressed information. There has recently been proposed in e.g. the US Patent No.4703352 a high efficiency encoding/decoding apparatus in which data containing a large quantity of information, such as picture information data, is encoded by a transmitting side and transmitted at an increased rate, and in which data received by the receiving side is decoded for generating the picture information having a picture quality close to that of the original transmitted picture. In the high efficiency encoding/decoding method, the two-dimensional picture is sampled in a two-dimensional space or by a temporal-spatial sampling and thinned or sub-sampled information is encoded for transmission. Among the examples of temporal-spatial sub-sampling is a so-called multiple sub-Nyquist sampling encoding system as proposed by Japan Broadcasting Corporation (NHK). With transmission by this method, the information is sub-sampled at the encoding time for transmission. The decoder interpolates the sub-sampled information based on the received information to re-construct the information. As a matter of fact, the decoding of the picture transmitted in this manner is by interpolation of the non-transmitted picture information by fixed taps and filters of fixed coefficients based on the transmitted information. If, however, the decoding is performed at the decoding side by the above-described hardware configuration, picture re-construction may or may not be achieved effectively by the interpolation depending on the widely variable type of the picture information, such as pictures containing areas of movement and still pictures. As a matter of fact, the decoded picture exhibits various inconveniences, such as blurring, jerkiness indicating non-spontaneous movements or time-space fluctuation such as movements in an object of a decoded picture. In general, if a picture in which the effects of the interpolation cannot be effectively introduced by the above-described fixed filter configuration, the picture on the receiving side experiences the above-described inconveniences and the picture quality is significantly degraded. US-A-4,788,589 discloses an encoding apparatus for encoding a digital image signal and transmitting encoded data, the apparatus comprising: means for performing temporal sub-sampling of an input digital image signal to extract every fifth field as sub-sampled reference fields to be transmitted; means for generating predictive co-efficients in accordance with the input digital image signal and the sub-sampled reference fields by performing a matrix calculation on the input digital image signal and the sub-sampled reference fields such that an error between the input digital image signal and a digital image signal produced using the sub-sampled reference fields is a minimum; and means for transmitting the sub-sampled reference fields and the predictive co-efficients as the encoded data. According to a first aspect of the present invention, there is provided an encoding apparatus for encoding a digital image signal and transmitting encoded data, said encoding apparatus comprising: means for performing spatial and temporal sub-sampling of an input digital image signal and outputting a sub-sampled digital image signal; means for generating predictive coefficients in accordance with the input digital image signal and the sub-sampled digital image signal; such that an error between the input digital image signal and a digital image signal produced using the sub-sampled digital image signal and the predictive coefficients is a minimum; and means for transmitting the sub-sampled digital image signal and the predictive coefficients as the encoded data. According to further aspects of the present invention, there are provided a corresponding decoding apparatus and encoding and decoding methods, as defined in the claims. Accordingly, in the hereinafter described embodiments, during encoding the unknown coefficients are found from the result of addition of the information concerning the results of interpolation processing represented by the linear first-order combination of the input digital information and unknown coefficients and the errors between the information concerning the results of interpolation and the information concerning the object of interpolation obtained from the input information by the least square method as a value which minimizes the errors. Embodiments of the present invention can provide a high efficiency encoding/decoding device whereby the input information may be adaptively encoded with a high compression ratio irrespective of the type of the input information and the transmitted information may be decoded with interpolation to produce the playback information without deterioration in the picture quality. The invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which:- Fig. 1 is a schematic block diagram showing a high efficiency encoding device which performs sampling to thin out picture information in a manner outside the scope of the present invention, but which is otherwise in accordance with the present invention. Fig.2 is a diagrammatic view for illustrating the operating principle of the high efficiency encoding device based on the block diagram of Fig.1. Fig.3 is a schematic block diagram of a high efficiency decoding device according to an embodiment of the present invention. Fig.4 is a diagrammatic view showing a pattern of pixels employed for coefficient calculation using pixels of four out of seven frames when transmitting the pixel information with 1/2 frame dropping with increase in the number of taps along the time scale and which is not in accordance with the present invention because there is no spatial sub-sampling. Fig.5 shows a pattern of the pixel information employed for actual transmission in accordance with the pattern shown in Fig.4. Fig.6 is a diagrammatic view similar to Fig.4 and showing an example of a sub-sampling pattern when transmitting the pixel information with 1/2 frame dropping and which is in accordance with the present invention. Fig.7 shows a pattern of the pixel information employed for actual transmission in accordance with the pattern shown in Fig.6. Fig.8 is a diagrammatic view showing a pattern of pixels required for calculating the coefficients illustrating temporal-spatial thinning by 1/2 using three frames and an actual pixel pattern and which is in accordance with the present invention. Fig.9 is a diagrammatic view showing an actual pixel pattern and a pattern of pixels required for coefficient calculation in case the number of taps is increased along the time domain and an offset is made for each frame by way of sub-sampling in a checkerboard pattern. Fig.10 is a diagrammatic view showing an actual pixel pattern and a pattern of pixels required for coefficient calculation in case the number of taps is increased along the time domain and an offset is made for each frame by way of sub-sampling mainly in the horizontal direction in a checkerboard pattern. Fig.11 is a diagrammatic view showing the sampling pattern of the pixels shown in Fig.10 in which pixel numbers are allocated to the pixels of the actual pixel pattern. Fig.12 is a schematic block circuit diagram showing a high efficiency encoding device according to the present invention. Fig.13 shows a sampling pattern for the case of 1/4 temporal - spatial sub-sampling. Fig.14 is a diagrammatic view showing a three-dimensional representation of the sampling pattern shown in Fig.13. Fig.15 is a schematic block circuit diagram showing a high efficiency decoding device according to the present invention. A high efficiency encoding device is hereinafter explained by referring to the schematic block diagram of Fig. 1. The encoding device of Fig. 1 performs sampling to thin out picture information in a manner outside the scope of the present invention, but the device is otherwise in accordance with the present invention. By way of an example, the high efficiency encoding device herein is applied to a picture processing device required to process a large quantity of data at an elevated speed. The high efficiency encoding device comprises a thinning or sub-sampling unit 11 as thinning means for performing a thinning operation on the input picture information and outputting the sub-sampled picture information, and a model-associated coefficient calculating unit 12 as unknown coefficient calculating means. The model-associated coefficient calculating unit 12 formulates simultaneous equations which will minimize the errors between the information to be interpolated (the information as the object of interpolation) obtained from the input information and the information resulting from the interpolation and solves the simultaneous equations to find the unknown coefficients. These unknown coefficients are those of an interpolation equation employed for finding the thinned reference information using the transmitted information which has not been thinned after the processing at the thinning sub-sampling unit 11. The present embodiment employs a linear first-order coupled model. The model refers to a 1/2 frame dropping with sub-sampling in the time scale direction which is not in accordance with the present invention because there is no spatial sub-sampling. The model-associated coefficient calculating unit 12 is made up of a normal equation generating unit 12a for formulating normal equations as simultaneous equations by performing sub-sample extraction of the information of a region subject to the pre-defined model, and a coefficient calculating unit 12b for finding the unknown coefficients contained in the normal equations by the pixel information supplied from the normal equation generating unit 12a by coefficient calculation as later explained. The interconnection of the high efficiency encoding device is explained by referring to Fig.1. The picture information corresponding to the input picture is supplied via an input terminal 10 to the thinning sub-sampling unit 11. The picture information is also supplied to the normal equation generating unit 12a of the model-associated coefficient calculating unit 12. The thinning sub-sampling unit 11 transmits encoded output signals as transmission pixels to a decoder via an output terminal 13 and a transmission cable, not shown, while also transmitting the encoded output signals to the normal equation generating unit 12a. The model-associated coefficient calculating unit 12 performs time-series transformation on the transmission pixels supplied by the normal equation generating unit 12a and the input picture and model formulation corresponding to the linear first-order coupled models to generate the normal equations. The normal equation generating unit 12a outputs the coefficients of the generated normal equations to the coefficient calculating unit 12b. The coefficient calculating unit 12b performs matrix calculation on the unknown coefficients included in the supplied coefficients in accordance with the conditions imposed by the least squares method to transmit the calculated unknown coefficients to the decoder via transmission means, such as cables, not shown. The operating principle of the high efficiency encoding device is explained by referring to Fig.2. In the example shown in Fig.2, when every other frame is dropped by sub-sampling along the time domain as described above to give a 1/2 frame system, a pixel y disposed at the center of an nth frame is found using pixels of an (n-1)th frame and an (n+1)th frame on either sides of the nth frame. In a previously defined space-time model, the (n-1)th to (n+1)th frames comprise blocks 15, 16 and 17 in the respective frames as one block. Of these, the blocks 15 and 17 are made up of nine input pixels x 1 to x 9 and x 10 to x 18 , respectively. The model is represented by linear first-order combination x i w i , that is input pixels x i multiplied by coefficients w i , where i = 1, ... 18. The value y 5 at the center of the nth frame is represented by the linear combination w 1 x 1 + w 2 x 2 + ... + w 18 x 18 of 18-tap input pixels. The coefficients w i in the linear combination are determined so as to give the least residue between the pixel to be found by interpolation and the pixel as found by interpolation. For finding the unknown coefficients w 1 , the input pixels x i , where i = 1, ... n, and associated real pixels y j , where j = 1, ... m, are substituted into the linear combination when the input picture is shifted pixel by pixel in the spatial direction. If a set of coefficients is found for each frame in this manner, there are obtained a number of simultaneous equations in which the number of linear first-order combinations of the actual pixels y corresponding to the input pixels x and the unknown coefficients w corresponds to the number of pixels for one frame coefficient. By these simultaneous equations, corresponding matrices X, Y and a matrix of coefficients W are produced. These matrices X, W and Y are expressed by The equation (4) of the linear first-order combination model represented by the matrices X, W and Y XW = Y is an observation equation consisting of m simultaneous equations. The number of the simultaneous equations is significantly larger than the number of taps in pre-set two frames. Basically, the unknown coefficients w may be found by solving the observation equation. The method employed for finding the unknown coefficients w is the least squares method. That is, the method for finding the unknown coefficients w consists in adding a matrix of residues E to the right side of the observation equation. Addition of the matrix of residues E to the observation equation gives a residual equation. XW = Y + E In the least squares method, a matrix of coefficients W is found which gives the least value of the squares of the elements of the residue matrix E, that is square errors. The condition for finding the most probable value of the elements w i of the coefficient matrix W from the equation of the residues (6) is to satisfy a condition of minimizing the sum of the squares of m residues associated with the pixels in the block. This relation may be expressed by an equation (7) e 1 ∂ e 1 ∂ w i + e 2 ∂ e 2 ∂ w i + ... + e m ∂ e m ∂ w i = o By solving the residue equation, the unknown coefficients w 1 , w 2 , ... w n as the elements of the coefficient matrix w satisfying the n number of the above given conditions are found. Consequently, the equations (8) ∂e j ∂w 1 = x j1 ∂e j ∂w 2 = x j2 ....... ∂e j ∂w n = x jn are found from the residue equation (6). If the conditions of the equation (7) are satisfied for each of n (i = 1, ... n), the equations (9) are obtained. From the equations (6) and (9), the normal equations are obtained. The equations (10) are simultaneous equations having a number of unknown values equal to n . In this manner, the unknown coefficients w i may be found as the most probable values. More precisely, the sum from j = 1 to m of products x ji x ji of input pixels x ij in the equation (10), where i = 1, 2, ...., n and j = 1, 2, ...., m, consists of a number of matrix elements. If the matrix is regular, the normal equation may be solved. The subscript i indicating the columns of the input pixel x ji is for each column of the matrix elements the subscript j is changed. It is a regular equation generating unit 12a that performs a sequence of operations of finding the normal equations. The regular equation generating unit 12a outputs the coefficients in their entirety to the coefficient calculating unit 12b. The coefficient calculating unit 12b finds the unknown coefficients w i , using e.g. the Gauss-Jordan elimination method, or draining method, to solve the simultaneous equations. The coefficient calculating unit 12b outputs the coefficient w i as found to an output terminal 14. If an optimum set of coefficients are found for each frame, as shown by an example of dropping of 1/2 frame, the transmitted information is the pixels of every other frame and the coefficient set for each of the thinned-out frames. It is noted that the amount of the coefficient information is negligible as compared to the amount of information of the pixels per frame. Thus the ratio of compression for 1/2 frame dropping is approximately 1/2. A high efficiency decoding device which is an embodiment of the present invention is explained by referring to the schematic block circuit diagram shown in Fig.3. The high efficiency decoding device is explained in connection with interpolating the received information thinned out by temporal-spatial sub-sampling and restoring the original information from the received information. In restoring the original information, the compressed information by 1/2 frame dropping is decoded by applying the linear first-order combination model to e.g. the picture processing device. The high efficiency decoding device is made up of a model-associated interpolation processing unit 20 as interpolation processing means and a time-series transforming unit 21 as time-series transforming means. The interpolation processing unit 20 substitutes the non-thinned transmission information in the reception information and the elements w i of the coefficient matrix W of the transmitted coefficients corresponding to the unknown coefficients in the interpolation equation into the interpolation equation for finding the information of the object pixel of interpolation having the unknown coefficients to generate the information for restoring the transmitted original information. The time-series transforming unit 21 restores the time-series information corresponding to the pre-transmission information using the information of the object of interpolation generated by the model-associated interpolation processing unit 20 and the transmitted information. The compressed picture information is the transmitted information which is supplied via an input terminal 18 to both the model-associated interpolation processing unit 20 and the time-series transforming unit 21. The elements w i of the coefficient matrix W, pre-calculated and transmitted by the transmitting side, are supplied via an input terminal 19 to the model-associated interpolation processing unit 20. The model-associated interpolation processing unit 20 performs interpolation on the information supplied thereto using a model of the linear first-order combination model, that is a model which is the same as that used a the transmitting side. The interpolating processing unit calculates the pixels of interpolation by the linear non-linear combination of the equation (4) from the set of the coefficients w i and the transmitted pixels. The model-associated interpolation processing unit 20 transmits the restored interpolated pixel to the time-series transforming unit 21. The time-series transforming unit 21 causes the transmitted pixel lost by sub-sampling in the corresponding pixel position using the pixel transmitted to the temporal-spatial sampling position prior to transmission and the interpolated picture. The time-series transforming unit 21 achieves the restoration of the picture information by this transforming operation. The above arrangement renders it possible to produce an interpolated pixel closer to the pre-transmission original picture than with the uniform filtering of the transmitted pixel subject to picture deterioration to restore the high efficiency compressed code data. With the use of the high efficiency encoding device and the high efficiency decoding device, the data encoded and compressed with a high efficiency may be restored without substantially any deterioration by the transmission of the thinned-out transmission pixels and the unknown coefficients conforming to the linear first-order combination. The thinned-out pixels may be obtained by direct interpolation shown in Fig.3. Although the 3-frame 18-tap linear first-order combination model has been employed in the above-described embodiment, it is also possible to make processing by increasing the number of sub-sampling taps in the temporal/spatial directions. If the number of taps along the time scale is increased and transmission is made with 1/2 frame dropping, all the pixels of even-numbered ones of seven frames T0 to T6 shown in Fig.4, for example, are transmitted, which is not in accordance with the present invention because there is no spatial sampling. Simultaneously, using 5 x 5 pixel blocks in a frame space of each of the even-numbered frames, pixel data at a position "+" of a non-transmitted frame T3 are calculated. Using a linear first-order combination model, represented by the product of the transmitted pixels and the unknown coefficients, the high efficiency encoding device calculates the coefficients transmitted to the high-efficiency decoding device. Among the seven frames T0 to T6, the frames employed in the calculation of the transmitted coefficients are the even-numbered frames T0, T2, T4 and T6 marked with 0, as described above. Calculations are performed by the linear first-order model using 5 x 5 pixel blocks in the four frames. The coefficients actually transmitted are calculated using taps w 1 to w 100 of the frames T0, T2, T4 and T6 shown in Fig.6, and decoding is performed in accordance with the linear first-order model based on the transmitted picture information and the coefficients. A different sampling technique employing spatial and temporal sub-sampling which is in accordance with the present invention is illustrated in Fig. 6. In transmitting the seven frames T0 to T6 by 1/2 frame dropping, the even-numbered pixels of the seven frames T0 to T6 are transmitted. Simultaneously, unknown coefficients for data of a pixel at a position "+" of the frame T3 in a one-frame space are calculated for each of the even frames in association with the linear first-order combination model. As for the pixels employed for coefficient calculation in the linear first-order combination model, only the pixels at the positions 0 in Fig.6 are thinned out in the space for calculating the unknown coefficients. Of the pixel array patterns obtained by thinning out in the space, there are two patterns, namely the frame patterns T0 and T6 and the frame patterns T2 and T4. In effect, pixels w 1 to w 50 of the four frames arrayed in a checkerboard pattern (T0, T2, T4 and T6 shown in Fig.7) are employed. The previously described systems employ a set of unknown coefficients for each frame. However, a plurality of sets of coefficients may be employed for each frame by sub-dividing each frame in the space depending on the local features of a given picture. Another sampling technique employing spatial and temporal sub-sampling which is in accordance with the present invention is illustrated in Fig. 8. For the 1/2 temporal/spatial sampling as described above, transmitted pixels are thinned by 1/2 of the total number of usual transmitted pixels of the frames T0, T1 and T2. The pixels employed for calculating the unknown coefficients are the patterns obtained by thinning out the transmitted pixels thinned out in the checkerboard pattern similar to the array of the transmitted pixels. As the pixel arraying patterns, the pixels in a given frame are sub-sampled in a checkerboard pattern with an offset from frame to frame. In effect, the pixels employed for calculating the unknown coefficients are 13 pixels w 1 to w 12 for frame T0, 12 pixels w 13 to w 25 for frame T1 and 12 pixels w 26 to w 38 for frame T2 shown in Fig.8. Sub-sampling of 13 pixels and sub-sampling of 12 pixels are alternately carried out in accordance with the above-described thinning-out pattern for every other frame for carrying out the calculation of unknown coefficients in association with the model. If the number of taps is to be increased along the time scale, the five frames T0, T1, T2, T3 and T4 shown in Fig.9 are employed and sub-sampling is performed in a checkerboard pattern with an offset for every other frame. In such case, 12 pixels are employed for even frames T0, T2 and T4 and 13 pixels are employed for odd frames T1, T3 and T5, for calculating the unknown coefficients. In such case, a sum total of 62 pixels are employed for a model and the same pixels as those employed for coefficient calculation are transmitted and processed with 1/2 temporal/spatial sampling. If the number of taps is to be increased along the spatial direction, the three frames T0, T1 and T2 shown in Figs.10 and 11 are employed and sub-sampling is performed in a checkerboard pattern with offset for every other frame. For the sub-sampling pattern, a model is presumed in which coefficient calculation is performed in the horizontal direction for accommodating the pictures moved in the horizontal direction, such as panning. For coefficient calculation, 23 pixels are employed for the even frames T0 and T2 and 22 pixels are employed for the odd frames T1. In such case, calculation of a sum total of 68 pixels are employed for calculating the unknown coefficients and the same pixels as those employed for coefficient calculation are transmitted by way of 1/2 temporal/spatial thinning. For these models, the models represented by the linear first-order combination, similar to that employed in the previous first embodiment, are employed. Pixel thinning in the time and space may also be undertaken in which case the pixels thinned to 1/4 by thinning 1/2 as described above and additional thinning in the temporal space are transmitted along with the coefficients and the transmitted picture is to be reproduced. The thinning pattern by 1/4 is that in which three of the four pixels usually transmitted in the line direction are thinned out as described subsequently. The thinning pattern is a pattern in which a pattern is completed with four fields with an offset from field to field. A high efficiency encoding device employing as shown in Figs. 13 and 14, the temporal/spatial sampling as described above according to a modification is explained by referring to a schematic block diagram of Fig.12. The present embodiment is again directed to a picture processing device and parts or components which are used in common as those used in the previously explained high efficiency encoding device are denoted by the same reference numerals and corresponding description is omitted for simplicity. The present high efficiency encoding device illustrates an arrangement for performing 1/4 temporal/spatial thinning. The high efficiency encoding device for performing temporal/spatial sub-sampling and compressing the thinned-out information for information transmission is made up of a thinning sub-sampling unit 11 for thinning the input picture information and outputting the thinned-out information, a first model-associated coefficient calculating unit 23 as unknown coefficient calculating means, an interpolating processing unit 24 as unknown interpolation coefficient calculating means and a second model associated coefficient calculating unit 25. The first model-associated coefficient calculating unit formulates simultaneous equations which will minimize the error between the information of the object pixel of interpolation as obtained from the input information and the results of the interpolating processing by interpolation by an equation of interpolation for finding the information of the thinned-out object pixel of interpolation using the non-thinned out transmission information following the processing by the sub--sampling unit 11, with the coefficients of the equation of interpolation remaining unknown, and solving the simultaneous equations to find the most probable values for the unknown coefficients. The interpolation processing unit 24 formulates simultaneous equations which will minimize the errors between reference information for the object pixel of interpolation and the information concerning the results of interpolation processing obtained by interpolating processing on the information of the object pixel of interpolation which has not been taken as the object of interpolation in the first model-associated coefficient calculating unit 23, using the picture information transmitted from the sub-sampling unit 11 and the input picture information which is the above-mentioned reference information, with the coefficients of the equation of interpolation remaining unknown, and solving the simultaneous equations to find most probable values of the unknown coefficients of interpolation which have not been interpolated. The reference information for the object of pixel interpolation is employed for performing reference comparison of the transmitted information from the thinning sub--sampling unit 11 and the information resulting from calculation of the information for the object of interpolation. The high efficiency encoding device includes a cascaded connection of the processing units 24 and 25 as one set downstream of the first model-associated coefficient calculating unit 23 for transmitting plural coefficients corresponding to the unknown coefficients and the transmitted information depending on the thinning amount by the sub-sampling unit 11. The high-efficiency encoding device is not limited to the present embodiment. If a hierarchical structure is employed in which a multi-stage thinning processing units are provided in the thinning sub-sampling unit 11 so that the non-thinned out transmission information outputted from a given stage is employed at the next following stage, it is possible to omit the processing unit 24 and to supply the transmitted information to the model-associated coefficient calculating unit related to the temporal-spatial thinning-out amounts. The first model-associated coefficient calculating unit 23 is made up of a first model-associated time-series transforming unit 23a for extracting sub-samples of the information conforming to a model pre-defined by time-series transformation for preparing normal equations satisfying the conditions for least square method, and a first coefficient processing unit 23b for performing coefficient calculation for unknown coefficients based on the picture information from the first model-associated time-series transforming unit 23a. The first coefficient processing unit 23b outputs coefficients 1 resulting from the calculation via an output terminal 14. The first coefficient processing unit 23b also outputs the coefficients 1 resulting from the calculation to the interpolation processing unit 24. Similarly to the first model-associated coefficient calculating unit 23, the second model-associated coefficient calculating unit 25 includes a second model-associated time-series transforming unit 25a and a second coefficient calculating unit 25b, although these units are not shown. The interconnection of the high efficiency encoding device is explained by referring to Fig.12. The picture information corresponding to the input picture is supplied via an input terminal 10 to the thinning sub-sampling unit 11. The picture information is also supplied to the first model-associated time-series transforming unit 23a of the first model-associated coefficient calculating unit 23. The thinning sub-sampling unit 11 outputs the encoded output signals as the transmitted information at the output terminal 13 while transmitting the encoded signals to the first model-associated time-series transforming unit 23a. The first model-associated coefficient calculating unit 23 performs time-series transformation on the transmission pixels supplied by the first model-associated time-series transforming unit 23a and the input picture and model formulation corresponding to the linear first-order coupled model to generate the normal equations. The first model-associated time-series transforming unit 23a outputs the coefficients of the generated normal equations to the first coefficient calculating unit 23b. The first coefficient calculating unit 23b performs matrix calculation on the unknown coefficients included in the supplied coefficients in accordance with the conditions imposed by the least squares method to output the calculated unknown coefficients at the output terminal 14. The coefficients calculated by the processing operation on the unknown coefficients are the coefficients 1 shown in Fig.8. The first coefficient calculating unit 23b transmits the coefficients 1 to the local decoder 24. The local decoder 24 finds the pixels which will be required in the subsequent 1/2 thinning model by interpolation using the thinned-out information from the thinning sub-sampling unit 11 and the coefficients 1. The local decoder 24 transmits the interpolating pixels as found out to the second model-associated coefficient calculating unit 25. In the present embodiment, the interpolated pixels correspond to the reference information for the object pixel of interpolation. The picture information supplied at the input terminal 10 is entered to the second model-associated coefficient calculating unit 25. The second model-associated coefficient calculating unit 25 performs time-series processing on the picture information and the interpolated pixels by the first model-associated time-series transforming unit 25a, not shown, and performs a processing operation corresponding to the linear first-order combination model from the processed information to formulate normal equations and the coefficients 1 constituting the normal equations are outputted to the second coefficient calculating unit 25b, not shown. The second coefficient calculating unit 25b calculates coefficients 2 as unknown coefficients corresponding to the linear first-order combination model to output the coefficients 2 at an output terminal 26. Referring to Figs.13 and 14, the operating principle of the high efficiency encoding device is explained. Each horizontal line in Fig.13 represents a scanning line for interlaced scanning. The thinning pattern is completed by four fields in the present embodiment and represents odd and even fields which stand for the fourth fields, with the odd field and the even field being shown on the same scanning lines by the solid and broken lines, respectively. The transmitted pixels in each of these fields are indicated by ○, , □ and ▪ for the first field #1, second field #2, third field #3 and the fourth field #4, respectively. It will be seen from Fig.13 that the pixels of the respective sampled and transmitted samples are arrayed in a checkerboard pattern and offset on the field basis. Fig.14 shows the sampling pattern shown in Fig.13 in a three-dimensional configuration. The sampling pattern shown in Fig.14 indicates that three of normally transmitted four pixels are thinned out in the line direction. The linear first-order combination model employed herein is such a model in which five fields are employed for constructing the model and coefficient calculation is performed on the field basis to find the unknown coefficients for the pixel to be interpolated. With the present model, the transmitted pixels, temporally and spatially thinned out by 1/4 as described above, are supplied on the field basis and the five-field transmitted pixels within a solid-line rectangle are employed for calculating unknown coefficients for finding the center pixel indicated by double circles as the pixel to be interpolated. Meanwhile, the pixels encircled by a broken-line rectangle broader than the solid-line rectangle, as indicated by fields #1 and #5, may be employed in the present model as the pixels employed in calculating the unknown coefficients. However, in such case, the number of the coefficients to be calculated is increased. The pixels not thinned out subsequent to the thinning by the sub-sampling unit 11 shown in Fig.12 are supplied in accordance with this model to the first model-associated time-series transforming unit 23a of the first model-associated time-series coefficient calculating unit 23. The transmission pixels supplied via the input terminal 10 are also supplied to the first model-associated time-series transforming unit 23a which then finds normal equations associated with the model based on the data supplied thereto to output the coefficients of the normal equations to the first coefficient calculating unit 23b. Based on these coefficients, the first coefficient calculating unit 23b performs a matrix operation to output the coefficients 1 as the most probable values which minimize the residues. The coefficients 1 are employed for the estimation of the center pixel in the 1/4 thinning. The coefficients 1 and the output of the thinning sub-sampling unit 11 are supplied to the local decoder 24. The local decoder 24 calculates the pixels to be interpolated in the model to supply the calculated pixel to be interpolated to the second model-related time-series transforming unit 25a. The normal equations associated with the linear first-order combination model for 1/2 thinning are found by the second model-related time-series transforming unit 25a. The coefficients thus found out are transmitted to the second coefficient calculating unit. The coefficients 2, which are unknown coefficients, are then found using the coefficients found by the least squares method by the second coefficient calculating unit 25b. The coefficients 2 used for estimating pixels on both sides of the center pixel in 1/2 thinning are outputted via the output terminal 26. The present high efficiency encoding device then outputs the thinned-out transmission pixels, coefficients 1 and 2 to effect high compression ratio transmission. Fig.15 shows, in a block diagram, an embodiment of a high efficiency decoding device in which the transmission information, such as the information on the object pixel of interpolation thinned out by temporal/spatial sub-sampling, the coefficients 1 and 2 are entered as the reception information and processed with interpolation for restoring the original information from the reception information. The cascaded multi-stage interconnection herein is the two-stage interconnection by employing the two sets of the coefficients, that is the coefficients 1 and 2. The high efficiency decoding device includes a first model-associated interpolating processing unit 30a and a first time-series transforming unit 30b as time-series transforming means for transforming the information of the object pixel of interpolation generated in the first model-associated interpolating unit 30a and the reception information into the time-series information corresponding to the pre-transmission information. The first model-associated interpolating processing unit 30a is the interpolating means for generating the information of the object of interpolation using the non-thinned transmission information in the reception information and one of the coefficients determined in association with the unknown coefficients in the equation of interpolation for finding the information of the object of interpolation. Although not shown, the second model-associated interpolating unit 31 is made up of a second model-associated interpolating unit 31a and a second time-series transforming unit 31b. In effect, the high efficiency decoding device shown in Fig.15 is made up of a multi-stage cascaded connection of a first model-associated interpolating processing unit 30 and a second model-associated interpolating processing unit 31. The first model-associated interpolating unit 30 is a first model-associated interpolating means for recovering the reception information using the transmission information in the reception information and the coefficients 2 which correspond to the unknown coefficients in the transmitted model and which represent the coefficients during 1/4 temporal/spatial sub-sampling. The second model-associated interpolating processing unit 31 is the second model-associated interpolating means adapted for performing model-associated interpolation for recovering the reception information using the interpolation information generated in the first model-associated interpolating unit 30 and the coefficients 1 which correspond to the unknown coefficients in the transmission model and which represent the coefficients 1 during 1/2 temporal/spatial sub-sampling. With the high efficiency decoding device shown in Fig.15, the thinned out transmission pixels are entered at an input terminal 27 to a first time-series transforming unit 30b and a first model-associated interpolating unit 30a in the first model-associated interpolating unit 30. The coefficients 2 are entered via an input terminal 28 to the first model-associated interpolating unit 30a. The first model-associated interpolating unit 30a performs interpolation corresponding to the linear first-order combination model and outputs the interpolated pixel thus found out to the first time-series transforming unit 30b. The first time-series transforming unit 30b performs time-series transformation on the transmission pixels and the interpolated pixels to transmit the processed pixels to model-associated interpolating processing unit 31. The second model-associated interpolating processing unit 31 performs the processing associated with the linear first-order combination model for 1/2 thinning on the coefficients 1 supplied via the input terminal 29 and an output of the first time-series transforming unit 30b. The unit 31 also performs time-series transformation thereon in the first model-associated interpolating unit 30a, for outputting a picture which is free from picture quality deterioration and which is extremely close to the original picture. The interpolating processing unit which performs such interpolating operation has a double-stage cascaded structure for calculating the coefficients for calculating the pixels of the information of the object of interpolation in the 1/4 temporal/spatial thinning and 1/2 temporal/spatial thinning at the encoder side for performing hierarchical interpolation from the transmitted pixels of the 1/4 temporal/spatial thinning. The decoder side arrangement is connected to the two-stage cascaded construction for finding the information of the object pixel of interpolation of each hierarchy for restoring the picture. By the interpolation, the restored picture is substantially free from picture quality deterioration by the operation of interpolation despite the hierarchical interpolation. There are two methods for producing a restoration picture substantially free from picture quality deterioration by interpolation from a transmitted picture which has been compressed by temporal/spatial sub-sampling. That is, there is a method of interpolating the center pixel and left and right side pixels by the arrangement of the high efficiency encoding and decoding devices shown in Figs.1 and 3, respectively, using three sets of coefficients, by way of direct interpolation, while there is a method of interpolation a center pixel by the arrangement of the high efficiency encoding and decoding device shown in Figs. 2 and 15 and of interpolating the center pixel by 1/2 - thinning linear combination model using two sets of coefficients, by way of hierarchical interpolation. It is possible with these methods to produce restoration pictures substantially free from picture quality deterioration by interpolation of non-transmitted pixels by the interpolation as will become clear from the above-described embodiments. In the above-described embodiments, the temporal/spatial thinning for hierarchical interpolation in the above-described embodiments of the high efficiency encoding and decoding devices, the temporal/spatial thinning is set to 1/4 and implemented by the two-stage cascaded connection. The present invention is not limited to such arrangement and it suffices to provide an n-stage cascaded connection necessary for the hierarchical interpolation for 1/2n temporal/spatial thinning, with n being 1, 2, ... . The compression ratio for the transmission information may be increased further by increasing the number of stages of the cascade connection. By forming a linear first-order combination model from the pixel to be interpolated and the transmitted pixels at the encoder side, employing the coefficients associated with the model as the unknown coefficients of the normal equations generated by the least squares method, calculating the most probable value and by transmitting the coefficients and the transmission pixels corresponding to the model suited to the picture of the object of transmission, it becomes possible to achieve transmission at a high compression ratio. On the other hand, by estimating the interpolated pixel by direct interpolation, interpolation of hierarchical structure or the like in dependence upon the linear first-order combination model from the transmission pixels and the coefficients at the decoder side, it becomes possible to produce the interpolated picture which is substantially free from deterioration in the picture quality and which is extremely close to the original picture as compared to the picture obtained by uniform filtering according to the conventional practice. In this manner, the original picture may be transmitted with a high compression ratio to produce an interpolated picture which is substantially free from picture quality deterioration.

Claims: An encoding apparatus for encoding a digital image signal and transmitting encoded data, said encoding apparatus comprising: means (11) for performing spatial and temporal sub-sampling of an input digital image signal and outputting a sub-sampled digital image signal; means (12) for generating predictive coefficients in accordance with the input digital image signal and the sub-sampled digital image signal; such that an error between the input digital image signal and a digital image signal produced using the sub-sampled digital image signal and the predictive coefficients is a minimum; and means (13, 14) for transmitting the sub-sampled digital image signal and the predictive coefficients as the encoded data. An encoding apparatus according to claim 1, wherein said generating means (12) comprises means (12a) for generating a plurality of linear first-order equations in accordance with the input digital image signal and the sub-sampled digital image signal such that an error between the input digital image signal and a digital image signal produced using the sub-sampled digital image signal and the predictive coefficients is a minimum; and means (12b) for generating the predictive coefficients by solving the plurality of linear first-order equations. An encoding apparatus according to claim 1 or 2, wherein said means (11) for performing sub-sampling is arranged to sub-sample pixels in different positions for every other frame. An encoding apparatus according to claim 3, wherein said means (11) for performing sub-sampling is arranged to sub-sample every other pixel in a checkerboard pattern offset for every other frame. A decoding apparatus for decoding encoded data including a sub-sampled digital image signal and predictive coefficients generated by an apparatus according to any one of the preceding claims, said decoding apparatus comprising: means for receiving a spatially and temporally sub-sampled digital image signal and predictive coefficients; and means for producing a restored digital image signal corresponding to the original digital image signal in accordance with the sub-sampled digital image signal and the predictive coefficients, comprising: means (20) for spatially and temporally interpolating pixel data by a linear combination calculation using a plurality of pixel data of said sub-sampled digital image signal and said predictive coefficients; and means (21) for producing said restored digital image signal constituted by pixel data of said sub-sampled digital image signal and interpolated pixel data. A transmission system comprising an encoding apparatus according to any one of claim 1 to 4 and a decoding apparatus according to claim 5. An encoding method for encoding a digital image signal and transmitting encoded data, said encoding method comprising the steps of : performing spatial and temporal sub-sampling of an input digital image signal and outputting a sub-sampled digital image signal; generating predictive coefficients in accordance with the input digital image signal and the sub-sampled digital image signal such that an error between the input digital image signal and a digital image signal produced using the sub-sampled digital image signal and the predictive coefficients is a minimum; and transmitting the sub-sampled digital image signal and the predictive coefficients as the encoded data. An encoding method according to claim 5, wherein said step of generating predictive coefficients comprises: generating a plurality of linear first-order equations in accordance with the input digital image signal such that an error between the input digital image signal and a digital image signal produced using the sub-sampled digital image signal and the predictive coefficients is a minimum; and generating the predictive coefficients by solving the plurality of linear first-order equations. An encoding method according to claim 7 or 8, wherein said step of performing sub-sampling comprises sub-sampling pixels in different positions for every other frame. An encoding method according to claim 9, wherein said step of performing sub-sampling comprises sub-sampling every other pixel in a checkerboard pattern offset for every other frame. A decoding method for decoding encoded data including a sub-sampled digital image signal and predictive coefficients generated by a method according to any one of claims 7 to 10, said decoding method comprising the steps of: receiving a spatially and temporally sub-sampled digital image signal and predictive coefficients; and producing a restored digital image signal corresponding to the original digital image signal in accordance with the sub-sampled digital image signal and the predictive coefficients by: spatially and temporally interpolating pixel data by a linear combination calculation using a plurality of pixel data of said sub-sampled digital image signal and said predictive coefficients; and generating said restored digital signal constituted by pixel data of said sub-sampled digital image signal and interpolated pixel data. A transmission method comprising an encoding method according to any one of claims 7 to 10 and a decoding method according to claim 11.

Inventors: KONDO TETSUJIRO, NAKAYA HIDEO, KONDO, TETSUJIRO, NAKAYA, HIDEO
Applicants: SONY CORP, SONY CORPORATION
Application year: 1993
Main classification: H04N7
IPC codes: H04N7