Abstract:
A video decoding device for a TV receiver, e.g., SDTV, decodes a compressed video signal transmitted from a transmitting side and displays the decoded signal. The device includes a first downsampling part for downsampling input data in a unit of block at a predetermined ratio; a display size converting part for dividing the downsampled result into a first group of data and a second group of data and after downsampling the first group of data, for performing screen format conversion for the downsampled first group of data into a display size; a memory for storing each of the converted first group of data and the second group of data; and an output part for downsampling the second group of data to correspond with the first group of data to thereby perform screen format conversion for the downsampled second group of data, when the second group of data is reproduced, and for outputting the first and second groups of data.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a decoding device, and more particularly, a video decoding device of a digital TV receiver. 
     2. Background of the Related Art 
     A moving pictures expert group (hereinafter “MPEG”) standard is recommended as an international standard for compressing and encoding of a digital moving video, preferably in a multimedia environment including digital versatile discs (DVDs) and digital TVs. Particularly, in current digital TVs, a high definition (hereinafter “HD”) grade of MPEG compression and restoration is accepted as a standard. Hence, an existing National Television System Committee (hereinafter “NTSC”) system type analog TV will be replaced with the digital TV. 
     Since the price of the HDTV is expensive at the start of the market initiation, a user&#39;s demand for a standard definition (hereinafter, referred to as “SD”) grade of TV will continue for a long period of time during the replacement of the NTSC type analog TV with the HDTV. The SD grade of TV, e.g., SDTV means a TV, or a settop box, which down-converts an HD grade of signal to display the down-converted signal on an SD grade of monitor, will be widely used. In addition to the HD grade of signal, the SDTV can receive the SD grade of signal. A standard for distinguishing the HD grade of signal and the SD grade of signal is dependent upon the number of picture elements (pels) which influences the determination of the video representation performance (a quality of image). 
     For instance, the SDTV or the settop box down-converts 1920 pels by 1080 lines 60 Hz interlaced scanning of the HD grade of signal to 720 pels by 480 lines 60 Hz interlaced scanning of the SD grade of signal, thus to display the down-converted HD grade of signal. Of course, the SDTV can display the 720 pels by 480 lines 60 Hz interlaced scanning of the SD grade of signal, without any conversion. 
     FIG. 1 is a block diagram illustrating a video decoding device in a digital HDTV receiver in the background art. In the typical video decoding device, one pel consists of 8 bits, one macroblock has data structure of 16×16 pels, and the bitstream having the corresponding level to each grade which contains motion vector information is processed. 
     A variable length decoder (hereinafter “VLD”)  101  performs a variable length decoding for bitstream of data inputted and divides the decoded result into motion vectors, quantizing values, and discrete cosine transform (hereinafter “DCT”) coefficients. An inverse quantizer (hereinafter “IQ”)  102  performs an inverse quantization for the DCT coefficients outputted from the VLD  101  and outputs the inverse-quantized result to an inverse DCT (hereinafter “IDCT”)  103 . 
     The IDCT  103  performs an inverse DCT on the inverse-quantized DCT coefficients and outputs the IDCT processed result to an adder  104 . The adder  104  adds motion compensated data to the IDCT processed data to thereby restore the added data to the complete video and then stores the restored video in a frame memory  106 . The restored video signal is outputted for display and simultaneously fed back to a motion compensator  105  for the motion compensation. The motion compensator  105  outputs an appropriate pel value of the frame memory  106  to the adder  104  by using the motion vectors outputted from the VLD  101 . 
     For the HDTV receiver, the video decoding device receives and restores the HD grade of data and also receives and decodes the SD grade of data, without any problem. However, the video decoding device of the SDTV receiver can receive and restore the SD grade of data without any problem, but the SDTV requires conversion of the HD grade of data to the SD grade of data. In other words, the video decoding device of the SD grade of TV receiver performs data conversion of the HD grade of data into the SD grade of data. The data conversion process is completed through downsampling, i.e., filtering/decimation. 
     FIG. 2 is a block diagram illustrating the video decoding device of the SD grade of TV receiver for such a conversion. The data block size of 8×8 (shown as  201 ) is reduced to data block size of 4×4. An IDCT/downsampler  202  performs the inverse discrete cosine transform for the vertical 8 pels in the data block size of 8×8 and for the horizontal 4 pels therein, to thereby reduce the data block size of 8×8 to the data block size of 8×4. 
     The thirty-two DCT coefficients, as shown by the black dot from the upper end of the data block  201 , are selected, and the inverse discrete cosine transform is performed to the 8×4 size of data block for the selected coefficients, thereby obtaining the downsampled image data. The coefficients in the data block size of 8×8 indicated by the white dots are discarded. As can be appreciated by one of ordinary skill, the methods of selecting the coefficients may vary. 
     The image data which is downsampled to the data block size of 8×4 is stored to a frame (or field) memory  204  through an adder  203 . To perform motion compensation, the image data of the frame memory  204  is horizontally upsampled to the data block size of 8×8 in an upsampler  205 . The upsampled image data is motion-compensated in a motion compensating circuit  206  by using the motion vectors information. Since the compensated data has the data block size of 8×8, a downsampler  207  performs a horizontal downsampling for the compensated data to a block size 8×4. As a result, the data downsampled to the block size of 8×4 is added to the adder  203 . Accordingly, the adder  203  outputs a desired video, e.g., the video downsampled to the data block size of 8×4. 
     The output value of the frame memory  204  is vertically downsampled to the data block size of 4×4 in a downsampler  208 . The downsampled data is outputted to a format converter  209 , which converts the downsampled data block size of 4×4 to be matched with the required size and aspect ratio to generate a final video output. 
     For example, assuming that the input video is the HD grade of 1080 lines and 1920 pels per line, the IDCT/downsampler  202  outputs 1080 lines and 960 pels per line and the downsampler  208  outputs 540 lines and 960 pels per line. Finally, the format converter  209  outputs 480 lines and 720 pels per line. 
     However, the conventional decoding device of the SD grade of digital TV receiver has various disadvantages. For example, since the HD grade of data is downsampled horizontally to ½ size, the size of the frame memory is reduced to ½ compared to the HD grade of decoder. Hence, the existing SD grade of decoder needs 4,590 kByte size memory which is half of the 9,180 kByte size memory of the HD grade of decoder. However, the 4,590 kByte size of the SDTV video decoder is larger than the standard 4 MByte DRAM, which increases cost. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to at least obviate one or more of the problems due to limitations and disadvantages of the related art or other conventional art. 
     Another object of the present invention is to decrease the memory size. 
     A further object of the present invention is to use standard memory size. 
     A further object of the invention is to convert HD signals to SD signals. 
     Still another object of the present invention is to decrease costs. 
     Another object of the invention is to provide a video decoding device of a digital TV receiver which separates pictures I and P from a picture B, downsamples each of the separated pictures and converts the downsampled pictures into a display size matched to a screen size and format, thus to have a small size of frame memory. 
     The present invention can be achieved in a whole or in parts by a video decoding device of a digital TV receiver that converts the picture B which is not an anchor frame into the display size matched to a screen aspect ratio and performs data encoding for the converted picture to thereby store the encoded result in a memory, and on the other hand, it performs data encoding for the pictures I and P to store the encoded result in the memory, whereby memory capacity required therein can be reduced. 
     The present invention can be achieved in a whole or in parts by a video decoding device of a digital TV receiver is that outputs the picture B after completion of data decoding and outputs the pictures I and P after completion of the data decoding and format conversion to an adequate screen size and aspect ratio, whereby the memory capacity required therein can be reduced and a high quality of picture can be ensured. 
     The present invention can be achieved in a whole or in parts by a device for a television that converts a first data format to a final data format, comprising a decoder circuit that receives the first data format at an input port and decodes the first data format to output a second data format and the final data format at first and second output ports; an encoder circuit that receives the second data format at an input port and encodes the second data format to output a third data format at an output port; and a memory coupled to the decoder and encoder, the memory storing the third data format received from the encoder and providing the third data format to said decoder circuit for decoding into the final data format. 
     The present invention can be achieved in a whole or in parts by a television receiver comprising a tuner for selecting a prescribed transmitted signal received via an antenna; a decoder for decoding a signal selected by the tuner into a bitstream of a first data format; a device that converts the first data format to a final data format; a display for displaying an image based on the final data format, wherein the device includes a decoder circuit that receives the first data format at an input port and decodes the first data format to output a second data format and the final data format at first and second output ports; an encoder circuit that receives the second data format at an input port and encodes the second data format to output a third data format at an output port; and a memory coupled to the decoder and encoder, the memory storing the third data format received from the encoder and providing the third data format to said decoder circuit for decoding into the final data format. 
     The present invention can be achieved in a whole or in parts by a method of decoding an input data of a television receiver, comprising the steps of downsampling the input data in a unit of block at a predetermined ratio; dividing the downsampled result into a first group of data and a second group of data and after downsampling the first group of data, performing screen format conversion of the downsampled first group of data for a display size and aspect ratio; storing in a memory each of the converted first group of data and the second group of data; downsampling the second group of data to correspond with the first group of data to thereby perform screen format conversion for the downsampled second group of data; and outputting the first and second groups of data when the second group of data is reproduced. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
     FIG. 1 is a block diagram illustrating the video decoding device of a digital HDTV receiver in the background art; 
     FIG. 2 is a block diagram illustrating the downsampling in a video decoding device of a digital SDTV receiver in the background art; 
     FIG. 3 is a block diagram illustrating a video decoding device of a digital TV receiver in accordance with a preferred embodiment of the present invention; 
     FIG. 4 is a block diagram illustrating the data encoding process in accordance with a preferred embodiment of the present invention; and 
     FIG. 5 is a block diagram of a TV receiver incorporating the preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In a preferred embodiment of the present invention, the I, P and B pictures are downsampled to a data size of 8×4, and after completion of downsampling to a data size of 4×4, format conversion and data encoding, the B picture is stored in a B frame memory. After completion of the data encoding, on the other hand, the I and P pictures are stored in an anchor frame memory. Thereafter, the B picture is data decoded to be displayed, and the I and P pictures are data decoded, downsampled to a data size of 4×4, and format converted, thus to be outputted together with the B picture. 
     As a result, a video decoding device according to a preferred embodiment of the present invention requires approximately 3 MByte frame memory, and the whole system can be embodied by using, e.g., 4 MByte DRAM. As can be appreciated, the examples of the downsampling ratio and the number of pels are not limited to the specific embodiments described in the present invention. 
     FIG. 3 is a block diagram illustrating the video decoding device of a SDTV, preferably digital, receiver constructed in accordance with a preferred embodiment of the present invention. In addition to a VLD and an IQ, an IDCT/downsampler  301  receives DCT coefficients (I, P and B pictures) of a data size of 8×8 and performs IDCT, filtering and horizontal-downsampling to thereby output a data size of 8×4. An adder  302  adds the data size of 8×4 to motion compensated data, and a switch  303  controls the outputs of the I, P and B pictures in a data size of 8×4 outputted from the adder  302 . 
     A display size converter  304  performs a vertical downsampling, format conversion and data encoding for the B picture selected in the switch  303  to thereby convert the display size of the B picture, while a data encoder  305  performs the data encoding for the I and P pictures selected in the switch  303 . A memory  306  comprises an anchor frame memory  306   a  to store the data encoded I and P pictures and a B frame memory  306   b  to store the converted display size of the B picture. A data decoder  307  performs data decoding for the data of I and P pictures outputted from the anchor frame memory  306   a . A horizontal upsampler  308  horizontally upsamples the decoded data of I and P pictures to thereby convert the data of size 8×4 into the data size of 8×8. 
     A motion compensator  309  performs a motion compensation by using the output of the horizontal upsampler  308  and motion vectors. A horizontal downsampler  310  horizontally downsamples the output of the motion compensator  309  to a data size of 8×4 to thereby the converted result to the adder  302 , and a data decoder  311  decodes the output of the B frame memory  306   b . A vertical downsampler  312  vertically downsamples the decoded data of I and P pictures in the data decoder  307  to thereby convert the data size of 8×4 into a data size of 4×4. A format converter  313  converts the output of the vertical downsampler  312  in accordance with the size and aspect ratio of the display device. 
     The display size converter  304  comprises a downsampler  304   a  for vertically downsampling the B picture selected in the switch  303 , a format converter  304   b  for converting the size and aspect ratio of the downsampled B picture for display, and a data encoder  304   c  for performing data encoding for the format converted data of the B picture. 
     FIG. 4 is a block diagram illustrating the data encoding process in accordance with a preferred embodiment of the present invention. As discussed, the IDCT/downsampler  301  performs the IDCT for the DCT coefficients received in a size data 8×8 and filters horizontally downsamples the IDCT processed data to the data size of 8×4. The downsampling of the data size of 8×4 is performed for the I, P and B pictures, and the downsampled data is outputted to the adder  302 . As can be appreciated, the downsampling and upsampling can be achieved in various manners. 
     The adder  302  adds the downsampled data size of 8×4 and the motion compensated data size of 8×4 and outputs the added result to the switch  303 . If the input is at least one I and P pictures, the switch  303  outputs the I and/or P pictures to the data encoder  305  and if the input is a B picture, the B picture is provided to the display size converter  304 . 
     The vertical downsampling, the format conversion and the data encoding for the B picture are performed in the display size converter  304 . The vertical downsampler  304   a  of the display size converter  304  performs the vertical downsampling for the data size of 8×4 of the B picture to the data size of 4×4 and outputs the downsampled data to the format converter  304   b . The format converter  304   b  performs size and aspect ratio conversion for the data size of 4×4 of the B picture to be matched to a display size and its aspect ratio. Thereafter, the data encoder  304   c  reduces the number of bits of the data for B picture and stores the reduced number of bits of data in the B frame memory  306   b  of the memory  306 . 
     The encoding for the reduction of the number of bits performed by the data encoder  304   c  are shown in FIG. 4, which is also applied to the data encoder  305  for the I and/or P pictures. As can be appreciated, the data decoding is completed in the reverse of the data encoding. As shown, the number of bits is reduced based on the limited capacity of the memory  306 , and a method of reducing the number of bits is based upon the correlation of pels adjacent thereto. In particular, the basic number of bits is a data size of 8×4 and is horizontally (or vertically) reduced to 14 bits in consideration of the correlation of the adjacent pixels. 
     An example of the method of reducing the number of bits is given with differential pulse code modulation (DPCM). In other words, the horizontal (or vertical) pels p 1 , p 2 , p 3  and p 4   401  of decoded image pels  400  are each encoded to p 1  (original value), p 2 -p 1  (difference value between adjacent pels), p 3  (original value), and p 4 -p 3  (difference value between adjacent pels)  402 . With the application of non-uniform quantization table  403 , the p 1  is encoded to an 8 bit value, the p 2 -p 1  to a 6 bit value, the p 3  to an 8 bit value, and the p 4 -p 3  to a 6 bit value. The encoded result  404  is stored in a corresponding frame memory  405 , which may be the anchor frame memory  306   a  or the B frame memory  306   b  shown in FIG.  3 . The reduced number of bits of data is stored in the B frame memory  306   b , and the stored data is decoded in the reverse of the data encoding in the data decoder  311  for the image restoration (representation). By the selection of the switch  303 , the number of bits of data of the I and P pictures is reduced by the data encoder  305 , which is stored in the anchor frame memory  306   a . Then, the stored data is decoded in the reverse of the data encoding in the data decoder  307  for the image restoration. 
     The data size of 8×4 decoded in the data decoder  307  is inputted to the horizontal upsampler  308  for the motion compensation, and the horizontal upsampler  308  horizontally upsamples the data size of 8×4 to the data size of 8×8 by using inputted motion vectors. The upsampled data size of 8×8 in the horizontal upsampler  308  is inputted to the motion compensator  309 , which compensates the motion of the data size of 8×8 by using the inputted motion vectors and outputs the compensated result to the horizontal downsampler  310 . 
     The horizontal downsampler  310  horizontally downsamples the motion compensated data size of 8×8 to the data size of 8×4 and supplies the downsampled data to the adder  302 . As a result, after the downsampling to the data size of 8×4 by the IDCT/downsampler  301 , the motion compensated signals of the I, P and B pictures matched to the data size of the I, P and B pictures are finally outputted. After repeating the above procedure, the data process for each of the frames of I, P and B pictures is completed. 
     On the other hand, the data size of 8×4 outputted and decoded from the anchor frame memory  306   a  is vertically downsampled to the data size of 4×4 (which is matched to the B picture downsampled to the data size of 4×4). Next, the format conversion for the I and P pictures is performed to be matched to the display size and its aspect ratio, and the format converted I and P pictures are outputted as a final video signal together with the data of B picture. 
     FIG. 5 illustrates an overall block diagram of a digital TV incorporating the video decoder in accordance with a preferred embodiment of the present invention. The TV includes a tuner and a channel decoder for receiving signals transmitted from a broadcasting station through, e.g., an antenna and decodes the signal. If the data is decoded in units of packets, a depacketizer separates a signal received from the tuner and channel decoder into a video and/or audio bitstream. The video bit stream is decoded by the video decoder in accordance with a preferred embodiment of the present invention and provided to a display. As can be appreciated, the video decoder can be implemented as a settop box for the TV or a PC add-in card. 
     A video decoding device of a SDTV receiver according to the present invention can store anchor frames I and P and a frame B in different methods, in receiving and processing the HD grade of video in the SDTV receiver using MPEG standard, and introduce a method of reducing the number of bits, such that the capacity of memory required can be reduced and the quality of image can be maintained. 
     The foregoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.