Video coding apparatus and decoding apparatus

• US 6,104,434 A
• Filed: 06/17/1997
• Issued: 08/15/2000
• Est. Priority Date: 10/24/1996
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Morimatsu, Eishi, Shimizu, Takahiro, Nakagawa, Akira, Kazui, Kimihiko
• Primary Examiner(s): BRITTON, HOWARD W
• Application Number:
  US08/877,508
• Time in Patent Office: 1,155 Days
• Field of Search: 348/403, 348/420, 348/409, 348/412, 348/413, 348/415, 348/416
• US Class Current: 375/240.16
• CPC Class Codes: H04N 19/105 Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
• CPC Class Codes: H04N 19/117 Filters, e.g. for pre-processing or post-processing sub-band filter banks H04N19/635
• CPC Class Codes: H04N 19/134 characterised by the element, parameter or criterion affecting or controlling the adaptive coding
• CPC Class Codes: H04N 19/139 Analysis of motion vectors, e.g. their magnitude, direction, variance or reliability
• CPC Class Codes: H04N 19/152 by measuring the fullness of the transmission buffer
• CPC Class Codes: H04N 19/159 Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/196 being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters processing of motion vectors H04N19/513
• CPC Class Codes: H04N 19/527 Global motion vector estimation
• CPC Class Codes: H04N 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/82 involving filtering within a prediction loop
• CPC Class Codes: H04N 19/86 involving reduction of coding artifacts, e.g. of blockiness

Abstract

Video coding apparatus and decoding apparatus capable of reproducing decoded pictures without introducing unwanted noises, even if any considerable difference in pixel values or discontinuity exists at a certain block boundary. In a video coding apparatus employing predictive techniques, a dequantizer and an inverse DCT processor reproduce a prediction error signal from quantized transform coefficients. Here, a first resolution conversion unit (or downsampling unit) might have subsampled the original prediction error signal to reduce its picture resolution. If this is the case, a second resolution conversion unit (or upsampling unit) attempts to restore the original resolution of the prediction error signal by applying an upsampling process to the reproduced prediction error signal having the reduced resolution. In this upsampling process, each new pixel value in a certain block are calculated with reference to some surrounding pixels. The upsampling process, however, will not refer to the pixels belonging to any adjacent blocks that are subject to another coding scheme which is different from the coding scheme of the present block of interest. As an alternate arrangement, the upsampling process will entirely neglect the pixels in any other blocks but will refer only to the present block.

Claims

1. A video coding apparatus for performing a predictive coding of digital video input signals, comprising:

(a) resolution determination means for selecting a picture resolution to be used in a video coding of a source picture of a current frame, the picture resolution being either a low resolution or a high resolution;

(b) decoded picture storage means for storing a past decoded picture reproduced in a previous frame;

(c) prediction parameter calculation means, coupled to said resolution determination means, for determining which of two coding schemes should be used to encode individual blocks, by comparing the source picture of the current frame with the past decoded picture stored in said decoded picture storage means, and also for calculating motion vectors of the blocks in the source picture, wherein

said two coding schemes include an intraframe coding and an interframe coding, and

said blocks are defined by partitioning a given picture into pieces according to the picture resolution determined by said resolution determination means;

(d) prediction picture generation means for producing a prediction picture through calculation of pixel values on a block-by-block basis, said calculation of the pixel values including

assignment of zeros to pixel values of the blocks subject to the intraframe coding, and

calculation of the pixel values of the other blocks subject to the interframe coding, based on the past decoded picture stored in said decoded picture storage means and the motion vectors obtained by said prediction parameter calculation means;

(e) prediction error signal generation means for producing a prediction error signal for each block by calculating differences between the source picture and the prediction picture;

(f) first resolution conversion means for downsampling the prediction error signal produced by said prediction error signal generation means to provide the low resolution, depending upon the picture resolution determined by said resolution determination means;

(g) orthogonal transformation/quantization means for applying an orthogonal transformation process and a quantization process to the prediction error signal processed by said first resolution conversion means;

(h) code allocation means for outputting a code word relevant to a given set of data, which code word is retrieved out of a predefined code word table, wherein

said given set of data includes at least the output of said orthogonal transformation/quantization means, the picture resolution determined by said resolution determine means, the coding scheme determined by said prediction parameter calculation means, and the motion vectors calculated by said prediction parameter calculation means, and

said predetermined code word table contains a plurality of cord words previously assigned to each possible combination of the given set of data;

(i) dequantization/inverse orthogonal transformation means for applying a dequantization process and an inverse orthogonal transformation process to the output of said orthogonal transformation/quantization means to reproduce the prediction error signal;

(j) second resolution conversion means for applying an upsampling process to the reproduced prediction error signal sent from said dequantization/inverse orthogonal transformation means to provide the high resolution, if the reproduced prediction error signal has the low resolution processed by said first resolution conversion means, wherein

said upsampling process, when calculating a pixel value in a block that is subject to one of the two coding schemes, does not refer to any pixels that belong to any other block adjacent to the block of interest if the adjacent block is subject to the other coding scheme, but refers at least to the pixels belonging to the block of interest; and

(k) decoded picture generation means for constructing a decoded picture by adding the reproduced prediction error signal processed by said second resolution conversion means to the prediction picture produced by said prediction picture generation means, and for outputting the decoded picture to said decoded picture storage means.

2. The video coding apparatus according to claim 1, wherein

said second resolution conversion means examines whether or not the block of interest is adjacent to any other block that is subject to the other coding scheme, based on the coding schemes of the individual blocks determined by said prediction parameter calculation means,

if the block of interest is not adjacent to the block that is subject to the other coding scheme, said second resolution conversion means executes the upsampling process for the reproduced prediction error signal to gain the high resolution, referring to values of the reproduced prediction error signal of the pixels belonging to the adjacent block and the pixels belonging to the block of interest, and

if the block of interest is adjacent to the block that is subject to the other coding scheme, said second resolution conversion means executes the upsampling process for the reproduced prediction error signal to gain the high resolution, referring to values of the reproduced prediction error signal of the pixels not belonging to the adjacent block being subject to the other coding scheme.

3. The video coding apparatus according to claim 1, wherein the said second resolution conversion means executes the upsampling process for the reproduced prediction error signal to gain the high resolution, referring to values of the reproduced prediction error signal of the pixels belonging only to the block of interest.

4. The video coding apparatus according to claim 1, further comprising high-frequency suppression means, disposed between said prediction picture generation means and said prediction error signal generation means, for suppressing a predetermined range of high frequency components contained in the prediction picture produced by said prediction picture generation means.

5. The video coding apparatus according to claim 4, wherein said high-frequency suppression means refers to the motion vectors calculated, one for each block, by said prediction parameter calculation means, so as to classify the blocks into a first group of blocks exhibiting fast motion and a second group of blocks exhibiting less active motion, and suppresses the high-frequency components only when the block of interest falls into the first group of blocks and said resolution determination means has determined the low resolution.

6. A video coding apparatus for performing a predictive coding of digital video input signals, comprising:

(a) resolution determination means for selecting a picture resolution to be used in a video coding of a source picture of a current frame, the picture resolution being either a low resolution or a high resolution;

(b) decoded picture storage means for storing a past decoded picture reproduced in a previous frame;

(c) prediction parameter calculation means, coupled to said resolution determination means, for determining which of two coding schemes should be used to encode individual blocks, by comparing the source picture of the current frame with the past decoded picture stored in said decoded picture storage means, and also for calculating motion vectors of the blocks in the source picture, wherein

said two coding schemes include an intraframe coding and an interframe coding, and

said blocks are defined by partitioning a given picture into pieces according to the picture resolution determined by said resolution determination means;

(d) prediction picture generation means for producing a prediction picture through calculation of pixel values on a block-by-block basis, said calculation of the pixel values including

assignment of zeros to pixel values of the blocks subject to the intraframe coding, and

calculation of the pixel values of the other blocks subject to the interframe coding, based on the past decoded picture stored in said decoded picture storage means and the motion vectors obtained by said prediction parameter calculation means;

(e) prediction error signal generation means for producing a prediction error signal for each block by calculating differences between the source picture and the prediction picture;

(f) orthogonal transformation means for obtaining transform coefficients by applying an orthogonal transform to the prediction error signal produced by said prediction error signal generation means, according to the picture resolution determined by said resolution determination means, and for extracting low frequency components of the obtained transform coefficients;

(g) quantization means for applying a quantization process to the output of said orthogonal transformation means;

(h) code allocation means for outputting a code word relevant to a given set of data, which code word is retrieved out of a predefined code word table, wherein

said given set of data includes at least the output of said quantization means, the picture resolution determined by said resolution determine means, the coding scheme determined by said prediction parameter calculation means, and the motion vectors calculated by said prediction parameter calculation means, and

said predetermined code word table contains a plurality of cord words previously assigned to each possible combination of the given set of data;

(i) dequantization/inverse orthogonal transformation means for applying a dequantization process and an inverse orthogonal transformation process to the output of said quantization means to reproduce the prediction error signal;

(j) high resolution conversion means for applying an upsampling process to the reproduced prediction error signal sent from said dequantization/inverse orthogonal transformation means to regain the high resolution, if the reproduced prediction error signal derives from the low frequency components of the transform coefficients extracted by said orthogonal transformation means, wherein

said upsampling process, when calculating a pixel value in a block that is subject to one of the two coding schemes, does not refer to any pixels that belong to any other block adjacent to the block of interest if the adjacent block is subject to the other coding scheme, but refers at least to the pixels belonging to the block of interest; and

(k) decoded picture generation means for constructing a decoded picture by adding the reproduced prediction error signal processed by said high resolution conversion means to the prediction picture produced by said prediction picture generation means, and for outputting the decoded picture to said decoded picture storage means.

7. The video coding apparatus according to claim 6, further comprising high-frequency suppression means, disposed between said prediction picture generation means and said prediction error signal generation means, for suppressing a predetermined range of high frequency components contained in the prediction picture produced by said prediction picture generation means.

8. The video coding apparatus according to claim 7, wherein said high-frequency suppression means refers to the motion vectors calculated, one for each block, by said prediction parameter calculation means, so as to classify the blocks into a first group of blocks exhibiting fast motion and a second group of blocks exhibiting less active motion, and suppresses the high-frequency components only when the block of interest falls into the first group of blocks and said resolution determination means has determined the low resolution as the picture resolution.

9. A video coding apparatus for performing a predictive coding of digital video input signals, comprising:

(a) resolution determination means for selecting a picture resolution to be used in a video coding of a source picture of a current frame, the picture resolution being either a low resolution or a high resolution;

(b) decoded picture storage means for storing a past decoded picture reproduced in a previous frame;

(c) prediction parameter calculation means, coupled to said resolution determination means, for determining which of two coding schemes should be used to encode individual blocks, by comparing the source picture of the current frame with the past decoded picture stored in said decoded picture storage means, and also for calculating motion vectors of the blocks in the source picture, wherein

said two coding schemes include an intraframe coding and an interframe coding, and

said blocks are defined by partitioning a given picture into pieces according to the picture resolution determined by said resolution determination means;

(d) prediction picture generation means for producing a prediction picture through calculation of pixel values on a block-by-block basis, said calculation of the pixel values including

assignment of zeros to pixel values of the blocks subject to the intraframe coding, and

calculation of the pixel values of the other blocks subject to the interframe coding, based on the past decoded picture stored in said decoded picture storage means and the motion vectors obtained by said prediction parameter calculation means;

(e) prediction error signal generation means for producing a prediction error signal for each block by calculating differences between the source picture and the prediction picture;

(f) low resolution conversion means for downsampling the prediction error signal produced by said prediction error signal generation means to provide the low resolution, depending upon the picture resolution determined by said resolution determination means;

(g) orthogonal transformation/quantization means for applying an orthogonal transformation process and a quantization process to the output of said low resolution conversion means;

(h) code allocation means for outputting a code word relevant to a given set of data, which code word is retrieved out of a predefined code word table, wherein

said given set of data includes at least the output of said orthogonal transformation/quantization means, the picture resolution determined by said resolution determine means, the coding scheme determined by said prediction parameter calculation means, and the motion vectors calculated by said prediction parameter calculation means, and

said predetermined code word table contains a plurality of cord words previously assigned to each possible combination of the given set of data;

(i) dequantization means for obtaining reproduced transform coefficients by applying a dequantization process to the output of said quantization means to reproduce the prediction error signal;

(j) inverse orthogonal transformation means for reproducing the prediction error signal by performing an inverse orthogonal transform by using the reproduced transform coefficients as low-frequency components and by assigning zeros as high-frequency components, depending upon the picture resolution determined by said resolution determination means; and

(k) decoded picture generation means for constructing a decoded picture by adding the reproduced prediction error signal obtained by said inverse orthogonal conversion means to the prediction picture produced by said prediction picture generation means, and for outputting the decoded picture to said decoded picture storage means.

10. The video coding apparatus according to claim 9, further comprising high-frequency suppression means, disposed between said prediction picture generation means and said prediction error signal generation means, for suppressing a predetermined range of high frequency components contained in the prediction picture produced by said prediction picture generation means.

11. The video coding apparatus according to claim 10, wherein said high-frequency suppression means refers to the motion vectors calculated by said prediction parameter calculation means, so as to classify the blocks into a first group of blocks exhibiting fast motion and a second group of blocks exhibiting less active motion, and suppresses the high-frequency components only when the block of interest falls into the first group of blocks and said resolution determination means has determined the low resolution.

12. A video coding apparatus for performing a predictive coding of digital video input signals, comprising:

(a) resolution determination means for selecting a picture resolution to be used in a video coding of a source picture of a current frame, the picture resolution being either a low resolution or a high resolution;

(b) decoded picture storage means for storing a past decoded picture reproduced in a previous frame;

(c) prediction parameter calculation means, coupled to said resolution determination means, for determining which of two coding schemes should be used to encode individual blocks, by comparing the source picture of the current frame with the past decoded picture stored in said decoded picture storage means, and also for calculating motion vectors of the blocks in the source picture, wherein

said two coding schemes include an intraframe coding and an interframe coding, and

said blocks are defined by partitioning a given picture into pieces according to the picture resolution determined by said resolution determination means;

(d) prediction picture generation means for producing a prediction picture through calculation of pixel values on a block-by-block basis, said calculation of the pixel values including

assignment of zeros to pixel values of the blocks subject to the intraframe coding, and

calculation of the pixel values of the other blocks subject to the interframe coding, based on the past decoded picture stored in said decoded picture storage means and the motion vectors obtained by said prediction parameter calculation means;

(e) prediction error signal generation means for producing a prediction error signal for each block by calculating differences between the source picture and the prediction picture;

(f) first resolution conversion means for downsampling the prediction error signal produced by said prediction error signal generation means to provide the low resolution, depending upon the picture resolution determined by said resolution determination means;

(g) orthogonal transformation/quantization means for applying an orthogonal transformation process and a quantization process to the prediction error signal processed by said first resolution conversion means;

(h) code allocation means for outputting a code word relevant to a given set of data, which code word is retrieved out of a predefined code word table, wherein

said given set of data includes at least the output of said orthogonal transformation/quantization means, the picture resolution determined by said resolution determine means, the coding scheme determined by said prediction parameter calculation means, and the motion vectors calculated by said prediction parameter calculation means, and

said predetermined code word table contains a plurality of cord words previously assigned to each possible combination of the given set of data;

(i) dequantization/inverse orthogonal transformation means for applying a dequantization process and an inverse orthogonal transformation process to the output of said orthogonal transformation/quantization means to reproduce the prediction error signal;

(j) second resolution conversion means for applying an upsampling process to the reproduced prediction error signal sent from said dequantization/inverse orthogonal transformation means to provide the high resolution, if the reproduced prediction error signal has the low resolution processed by said first resolution conversion means;

(k) prediction picture modification control means for determining whether or not to modify values of pixels located in a neighborhood of a critical block boundary as part of the prediction picture produced by said prediction picture generation means, if the reproduced prediction error signal has the low resolution processed by said first resolution conversion means,

(l) prediction picture modification means for determining a new value of a pixel in a block that is adjacent to the critical block boundary, with reference to other pixels in another block adjacent to the block of interest; and

(m) decoded picture generation means for constructing a decoded picture by adding the reproduced prediction error signal processed by said second resolution conversion means to the prediction picture processed by said prediction picture modification means, and for outputting the decoded picture to said decoded picture storage means.

13. The video coding apparatus according to claim 12, wherein

said critical block boundary is defined as a boundary where the blocks constituting the prediction picture produced by said prediction picture generation means exhibit a critical difference in terms of pixel values, and

said prediction picture modification control means analyzes each block in the prediction picture to find the critical block boundary and, if the critical block boundary is found, determines that the pixels in the neighborhood thereof should be modified.

14. The video coding apparatus according to claim 13, wherein

said prediction picture modification control means, when analyzing a block of the prediction picture that is subject to one of the coding schemes, examines whether the block of interest is adjacent to any other block that is subject to the other coding scheme, based upon the coding schemes of the individual blocks determined by said resolution determination means, and

if said other block is found, said prediction picture modification control means recognizes that there exists the critical difference between the block of interest and the other block adjacent thereto.

15. The video coding apparatus according to claim 13, wherein

said prediction picture modification control means, when analyzing a block of the prediction picture, compares the motion vector of the block of interest with the motion vector of any adjacent block, based upon the motion vectors of the individual blocks calculated by said prediction parameter calculation means, and

if a difference between the two motion vectors compared is larger than a predetermined threshold, said prediction picture modification control means recognizes that there exists the critical difference between the block of interest and the adjacent block.

16. The video coding apparatus according to claim 12, further comprising high-frequency suppression means, disposed between said prediction picture generation means and said prediction error signal generation means, for suppressing a predetermined range of high frequency components contained in the prediction picture produced by said prediction picture generation means.

17. The video coding apparatus according to claim 16, wherein said high-frequency suppression means refers to the motion vectors calculated, one for each block, by said prediction parameter calculation means, so as to classify the blocks into a first group of blocks exhibiting fast motion and a second group of blocks exhibiting less active motion, and suppresses the high-frequency components only when the block of interest falls into the first group of blocks and said resolution determination means has determined the low resolution.

18. A video coding apparatus for performing a predictive coding of digital video input signals, comprising:

(a) resolution determination means for selecting a picture resolution to be used in a video coding of a source picture of a current frame, the picture resolution being either a low resolution or a high resolution;

(b) decoded picture storage means for storing a past decoded picture reproduced in a previous frame;

(c) prediction parameter calculation means, coupled to said resolution determination means, for determining which of two coding schemes should be used to encode individual blocks, by comparing the source picture of the current frame with the past decoded picture stored in said decoded picture storage means, and also for calculating motion vectors of the blocks in the source picture, wherein

said two coding schemes include an intraframe coding and an interframe coding, and

said blocks are defined by partitioning a given picture into pieces according to the picture resolution determined by said resolution determination means;

(d) prediction picture generation means for producing a prediction picture through calculation of pixel values on a block-by-block basis, said calculation of the pixel values including

assignment of zeros to pixel values of the blocks subject to the intraframe coding, and

calculation of the pixel values of the other blocks subject to the interframe coding, based on the past decoded picture stored in said decoded picture storage means and the motion vectors obtained by said prediction parameter calculation means;

(e) prediction error signal generation means for producing a prediction error signal for each block by calculating differences between the source picture and the prediction picture;

(f) first resolution conversion means for downsampling the prediction error signal produced by said prediction error signal generation means to provide the low resolution, depending upon the picture resolution determined by said resolution determination means;

(g) orthogonal transformation/quantization means for applying an orthogonal transformation process and a quantization process to the prediction error signal processed by said first resolution conversion means;

(h) code allocation means for outputting a code word relevant to a given set of data, which code word is retrieved out of a predefined code word table, wherein

said given set of data includes at least the output of said orthogonal transformation/quantization means, the picture resolution determined by said resolution determine means, the coding scheme determined by said prediction parameter calculation means, and the motion vectors calculated by said prediction parameter calculation means, and

said predetermined code word table contains a plurality of cord words previously assigned to each possible combination of the given set of data;

(i) dequantization/inverse orthogonal transformation means for applying a dequantization process and an inverse orthogonal transformation process to the output of said orthogonal transformation/quantization means to reproduce the prediction error signal;

(j) second resolution conversion means for applying an upsampling process to the reproduced prediction error signal sent from said dequantization/inverse orthogonal transformation means to provide the high resolution, if the reproduced prediction error signal has the low resolution processed by said first resolution conversion means;

(k) prediction picture modification means for determining new values of pixels in a block that is adjacent to a block boundary, with reference to other pixels in another block adjacent to the block of interest, if the reproduced prediction error signal has the low resolution processed by said first resolution conversion means; and

(l) decoded picture generation means for constructing a decoded picture by adding the reproduced prediction error signal processed by said second resolution conversion means to the prediction picture processed by said prediction picture modification means, and for outputting the decoded picture to said decoded picture storage means.

19. A video decoding apparatus for reproducing original motion pictures by decoding a predictive-coded digital video signal that has been received, comprising:

(a) reproduction means for reproducing at least quantized coefficients, picture resolution, coding scheme, and motion vectors from the predictive-coded digital video signal that has been received, wherein said coding scheme is either an intraframe coding or an interframe coding;

(b) decoded picture storage means for storing a past decoded picture reproduced in a previous frame;

(c) prediction picture generation means for producing, with reference to the coding scheme reproduced by said reproduction means, a prediction picture through computation of pixel values of each block by

assigning zeros to pixel values of the blocks subject to the intraframe coding, and

calculating the pixel values of the other blocks subject to the interframe coding, based on the past decoded picture stored in said decoded picture storage means and the motion vectors reproduced by said reproduction means,

wherein said each block is a part of the prediction picture that is partitioned according to the picture resolution reproduced by said reproduction means;

(d) dequantization/inverse orthogonal transformation means for applying a dequantization process and an inverse orthogonal transformation process to the quantized coefficients reproduced by said reproduction means, to obtain a reproduced prediction error signal;

(e) high resolution conversion means for applying an upsampling process to the reproduced prediction error signal obtained by said reproduction means to regain a high resolution, if the reproduced prediction error signal has originally been downsampled to a low resolution at a sending end where the predictive-coded digital video signal originated, wherein

said upsampling process, when calculating a pixel value in a block that is subject to one of the two coding schemes, does not refer to any pixels that belong to any other block adjacent to the block of interest if the adjacent block is subject to the other coding scheme, but refers at least to the pixels belonging to the block of interest; and

(f) decoded picture generation means for constructing a decoded picture by adding the reproduced prediction error signal processed by said high resolution conversion means to the prediction picture produced by said prediction picture generation means, and for outputting the decoded picture to said decoded picture storage means.

20. A video decoding apparatus for reproducing original motion pictures by decoding a predictive-coded digital video signal that has been received, comprising:

(a) reproduction means for reproducing at least quantized coefficients, picture resolution, coding scheme, and motion vectors from the predictive-coded digital video signal that has been received, wherein said coding scheme is either an intraframe coding or an interframe coding;

(b) decoded picture storage means for storing a past decoded picture reproduced in a previous frame;

(c) prediction picture generation means for producing, with reference to the coding scheme reproduced by said reproduction means, a prediction picture through computation of pixel values of each block by

assigning zeros to pixel values of the blocks subject to the intraframe coding, and

calculating the pixel values of the other blocks subject to the interframe coding, based on the past decoded picture stored in said decoded picture storage means and the motion vectors reproduced by said reproduction means,

wherein said each block is a part of the prediction picture that is partitioned according to the picture resolution reproduced by said reproduction means;

(d) dequantization/inverse orthogonal transformation means for applying a dequantization process and an inverse orthogonal transformation process to the quantized coefficients reproduced by said reproduction means, to obtain a reproduced prediction error signal;

(e) high resolution conversion means for applying an upsampling process to the reproduced prediction error signal obtained by said reproduction means to regain a high resolution, if the reproduced prediction error signal has originally been downsampled to a low resolution at a sending end where the predictive-coded digital video signal originated;

(f) prediction picture modification control means for determining whether or not to modify values of pixels located in a neighborhood of a critical block boundary as part of the prediction picture produced by said prediction picture generation means, if the reproduced prediction error signal has originally been downsampled to the low resolution at the sending end;

(l) prediction picture modification means for determining a new value of a pixel in a block that is adjacent to the critical block boundary, with reference to other pixels in another block adjacent to the block of interest, if the reproduced prediction error signal has originally been downsampled to the low resolution at the sending end and if said predicted picture modification control means determined to modify the values of the pixels located in the neighborhood of the critical block boundary; and

(m) decoded picture generation means for constructing a decoded picture by adding the reproduced prediction error signal processed by said high resolution conversion means to the prediction picture processed by said prediction picture modification means, and for outputting the decoded picture to said decoded picture storage means.

21. A video coding method to perform a predictive coding of a digital video input signal, comprising the steps of:

(a) determining a picture resolution to be used in a video coding of a source picture, the picture resolution being either a low resolution or a high resolution;

(b) partitioning a frame of the digital video input signal into a plurality of blocks;

(c) converting resolution of each block, which is obtained in said step (b), down to the low resolution, according to the picture resolution determined by said resolution determination means; and

(d) predictively coding the plurality of blocks whose resolution is converted to the low resolution in said step (c) by applying either one of a plurality of coding schemes on a block-by-block basis, comprising the substep of

(d1) performing an upsampling process of each block with the low resolution to regain the high resolution, while not referring, when calculating a pixel value in a block that is subject to one of the coding schemes, to any pixels that belong to any other block adjacent to the block of interest if the adjacent block is subject to the other coding scheme, but referring at least to the pixels belonging to the block of interest.

22. A video decoding method to reproduce original motion pictures by decoding a predictive-coded digital video signal that has been received, comprising the steps of:

(a) reproducing at least coding schemes each having been applied to blocks constituting a picture, out of the predictive-coded digital video signal that has been received; and

(b) predictively decoding the predictive-coded digital video signal according to the coding schemes reproduced in said step (a), to reproduce the picture on a block-by-block basis, comprising the substep of

(b1) performing an upsampling process of each block with the low resolution to regain the high resolution, while not referring, when calculating a pixel value in a block that is subject to one of the coding schemes, to any pixels that belong to any other block adjacent to the block of interest if the adjacent block is subject to the other coding scheme, but referring at least to the pixels belonging to the block of interest.