JPH11252561A - Moving image decoding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an encoding method capable of reducing an arithmetic operation quantity by lowering the precision of reverse DCT to a B-picture compared with the precision of reverse DCT to a an I-picture or a P-picture so as to be suitable for obtaining the reproduced picture with resolution lower than that of an original picture. SOLUTION: The DCT coefficient of the high-frequency part of a horizontal frequency among DCT coefficients to the I or P-picture is replaced with 0 and undergoes reverse DCT, and the DCT coefficients of the respective high- frequencies of a horizontal frequency and a vertical frequency among DCT coefficients to the B-picture are replaced with 0 and undergo reverse DCT, thereby the precision of reverse DCT to the B-picture is made lower than the precision of reverse DCT to the I or P-picture. In this MPEG decoder, a reverse DCT circuit 6 executes the reverse DCT of 8×8 for the DCT coefficient of the number of 8×8 generated by a zero replace-processing part for IP 4 or a zero replace-processing part for B 5 in order to generate data consisting of the number of data of 8 (the number of pixels in a horizontal direction)×8 (the number of pixels in a vertical direction).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving picture decoding apparatus and, more particularly, to a moving picture decoding apparatus which decodes a signal compressed and encoded by the MPEG system and obtains a reproduced picture having a resolution lower than that of an original picture. The present invention relates to an image decoding method.

[0002]

2. Description of the Related Art A moving picture expert group (MPEG) method has been conventionally known as an image coding method for compressing and coding image data in the field of digital TV and the like.

A typical MPEG system is MPEG.
1 and MPEG2. In MPEG1, only progressively scanned (non-interlaced) images were handled.
In PEG2, not only images of progressive scanning but also images of interlaced scanning have been handled.

[0004] Motion-compensated prediction (temporal compression), DCT (spatial compression), and entropy coding (variable-length coding) are employed for encoding these MPEGs. MP
In EG encoding, first, 16 (the number of pixels in the horizontal direction) × 1
For each macroblock having a size of 6 (the number of pixels in the vertical direction), prediction coding in the time axis direction (frame prediction coding in MPEG1 and frame prediction coding or field prediction coding in MPEG2) is performed. 3 pictures of I picture, P picture and B picture corresponding to the predictive coding method
There are different image types. In the following, a description will be given of frame predictive coding as an example.

(1) I picture: A picture coded from only the information in the frame and generated without performing inter-frame prediction. All macroblock types in the I picture are Intra-frame predictive coding in which coding is performed using only information.

(2) P picture: A picture formed by performing prediction from an I or P picture. In general, the macroblock type in a P picture is an intra-frame code which is encoded only with intra-frame information. And forward inter-frame prediction coding predicted from a past reproduced image.

(3) B picture: a picture made by bidirectional prediction, which generally includes the following macroblock types. a. Intra-frame predictive coding using only intra-frame information b. Forward inter-frame predictive coding predicted from past reproduced images c. Reverse interframe predictive coding predicting from the future d. Interpolative inter-frame prediction coding by both forward and backward prediction Here, the interpolative inter-frame prediction refers to averaging two predictions, forward prediction and backward prediction, between corresponding pixels.

[0008] In the MPEG encoder, the image data of the original image is 16 (the number of pixels in the horizontal direction) x 16 (the number of pixels in the vertical direction).
Is divided into macroblock units of size. For a macroblock whose macroblock type is not intra-frame predictive coding, inter-frame prediction according to the macroblock type is performed, and prediction error data is generated.

The image data for each macroblock unit (when the macroblock type is intra-frame predictive coding) or prediction error data (when the macroblock type is inter-frame predictive coding) is 8 × 8 The image data of each sub-block is divided into four sub-blocks, and a two-dimensional discrete cosine transform (DCT), which is a type of orthogonal transform, is performed on the image data of each sub-block based on Equation 1. That is, as shown in FIG.
Each DCT (orthogonal transform) coefficient F (u, v) in the uv space (u: horizontal frequency, v: vertical frequency) is obtained based on each data f (i, j) in a block of size.

[0010]

(Equation 1)

In MPEG1, the DCT contains a frame D
Although only the CT mode is used, the MPEG2 frame structure allows switching between the frame DCT mode and the field DCT mode in macroblock units. However, in the field structure of MPEG2, the field DC
Only T mode.

In the frame DCT mode, a 16 × 16 macro block is divided into four and divided into upper left 8 × 8 blocks, upper right 8 columns and 8 rows, lower left 8 × 8 blocks and lower right 8 × 8 blocks. DCT is performed for each block.

On the other hand, in the field DCT mode, 16
An 8 × 8 data group consisting of only odd lines in the left half 8 (the number of pixels in the horizontal direction) × 16 (the number of pixels in the vertical direction) of the left half of the × 16 macroblock, and in the 8 × 16 block of the left half An 8 × 8 data group consisting of only even-numbered lines, an 8 × 8 data group consisting only of odd-numbered lines in a right half of 8 (number of horizontal pixels) × 16 (number of vertical pixels) blocks, and a right half of 8 For each data group of an 8 × 8 data group consisting only of even lines in a × 16 block, D
CT is performed.

[0014] The DCT coefficients obtained as described above are quantized to generate quantized DCT coefficients. The quantized DCT coefficients are zigzag-scanned or alternate-scanned, arranged one-dimensionally, and encoded by a variable-length encoder. The MPEG encoder outputs control information including information indicating a macroblock type and a variable length code of a motion vector together with a variable length code of a transform coefficient obtained by the variable length encoder.

FIG. 5 is a block diagram showing the configuration of the MPEG decoder.

The variable-length code of the transform coefficient is sent to a variable-length decoder 101. Control signals including the macroblock type are sent to CPU 110. The variable length code of the motion vector is sent to the variable length decoder 109 and decoded. The motion vector obtained by the variable length decoder 109 is sent to the first reference image memory 106 and the second reference image memory 107 as a control signal for controlling the cutout position of the reference image.

The variable length decoder 101 decodes a variable length code of a transform coefficient. The inverse quantizer 102 converts the transform coefficients (quantized DCTs) obtained from the variable-length decoder 101
) Is inversely quantized and converted into DCT coefficients.

The inverse DCT circuit 103 includes an inverse quantizer 102
The DCT coefficient sequence generated in step (1) is returned to DCT coefficients in units of 8 × 8 sub-blocks, and 8 × 8 inverse DCT is performed based on the inverse transform equation shown in Expression 2. That is, as shown in FIG. 6, based on an 8 × 8 DCT coefficient F (u, v),
Data f (i, j) in units of 8 × 8 sub-blocks is obtained. Further, data f (i, i,
Based on j), reproduced image data or prediction error data in one macroblock unit is generated.

[0019]

(Equation 2)

The prediction error data generated in the macroblock unit by the inverse DCT circuit 103 is added with reference image data corresponding to the macroblock type by the adder 104.
And reproduced image data is generated. The reference image data is added to the adder 104 via the switch 112.
Sent to However, if the data output from the inverse DCT circuit 103 is reproduced image data for the intra-frame prediction code, the reference image data is not added.

The image data in macroblock units obtained by the inverse DCT circuit 103 or the adder 104 is
If the image data is reproduction image data for a picture, the reproduction image data is sent to the switch 113.

If the reproduced image data in macroblock units obtained by the inverse DCT circuit 103 or the adder 104 is reproduced image data for an I picture or a P picture, the reproduced image data is set to the switch 11.
1 is stored in the first reference image memory 106 or the second reference image memory 107. The switch 111
It is controlled by the CPU 110.

The averaging unit 108 includes memories 106 and 107
The reference image data used in the interpolative inter-frame predictive encoding is generated by averaging the reproduced image data read from.

The switch 112 is controlled by the CPU 110 as follows. If the data output from the inverse DCT circuit 103 is reproduced image data for the intra-frame prediction code, the common terminal of the switch 112 is switched to the ground terminal.

When the data output from the inverse DCT circuit 103 is prediction error data for a forward inter-frame prediction code or prediction error data for a reverse inter-frame prediction code, the common terminal of the switch 112 Switching is performed so as to select either the terminal to which the output of the first reference image memory 106 is sent or the terminal to which the output of the second reference image memory 107 is sent. When the reference images are read from the reference image memories 106 and 107, the cut-out position of the reference image is controlled based on the motion vector from the variable length decoder 109.

When the data output from the inverse DCT circuit 103 is prediction error data for an interpolative inter-frame prediction code, the common terminal of the switch 112 is connected to the averaging unit 1
It is switched to select the terminal to which the output of 08 is sent.

The switch 113 reproduces the reproduced picture data for the B picture sent from the adder 104, the reproduced picture data for the I picture or P picture stored in the reference picture memory 106, and the reproduced picture data stored in the reference picture memory 107. The CPU 110 controls the reproduced image data for the I picture or the P picture so as to be output in the same order as the order of the original images. The image data output from the decoder is provided to the monitor device, and the original image is displayed on the display screen of the monitor device.

[0028]

SUMMARY OF THE INVENTION An object of the present invention is to provide a moving picture decoding method suitable for obtaining a reproduced picture having a lower resolution than that of an original picture and capable of reducing the amount of calculation. .

[0029]

A moving picture decoding method according to the present invention is a moving picture decoding method for decoding a signal compressed by the MPEG system. It is characterized in that the accuracy is lower than the accuracy of inverse DCT for a picture.

Specifically, the following two methods (1)
There is (2).

(1) The DCT coefficient of the high frequency band of the DCT coefficient for the I picture or P picture is replaced with 0, and then the inverse DCT is performed. By performing the inverse DCT after replacing the DCT coefficient in the high frequency part of the vertical frequency with 0, the inverse DCT for the B picture is performed.
Is the inverse DC for I or P pictures.
Lower than the accuracy of T.

If the DCT transform is performed in units of blocks each having M pixels in the horizontal direction and N pixels in the vertical direction at the time of encoding the original image, for example, an M × N conversion for an I picture or a P picture is performed. After the DCT coefficients of the DCT coefficients in the block unit whose horizontal frequency is higher than M / 2 are replaced with 0, the inverse DCT is performed, and the horizontal frequency of the M × N block unit DCT coefficients for the B picture is M The inverse DCT is performed after replacing the DCT coefficients of the higher frequency portion than / 2 and the vertical frequency portion higher than N / 2 with 0. An example of M and N is M = N = 8.

(2) After removing the DCT coefficient of the high frequency part of the horizontal frequency among the DCT coefficients for the I picture or P picture, inverse DCT is performed, and the high frequency part and the vertical part of the DCT coefficient of the B picture for the B picture are removed. By performing the inverse DCT after removing the DCT coefficient in the high frequency part, the accuracy of the inverse DCT for the B picture is made lower than the accuracy of the inverse DCT for the I picture or the P picture.

At the time of encoding the original image, if the DCT transform is performed in units of blocks each having the number of horizontal images of M and the number of vertical pixels of N, for example, an M × N image for an I picture or a P picture After removing the DCT coefficients of the block whose horizontal frequency is higher than M / 2 among the DCT coefficients in block units, inverse DCT is performed, and the M
The inverse DCT is performed after removing the DCT coefficients of the DCT coefficients of the × N block unit in the horizontal frequency range higher than M / 2 and the vertical frequency range higher than N / 2. M,
An example of N is M = N = 8.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an MPEG decoder will be described below with reference to FIGS.

FIG. 1 shows the configuration of the MPEG decoder.

The variable length code of the transform coefficient is sent to the variable length decoder 1. The control signal including the macroblock type is sent to the CPU 20. The variable length code of the motion vector is sent to the variable length decoder 17 and decoded. The motion vector obtained by the variable length decoder 17 is sent to a vector value conversion circuit 18 and converted so that the horizontal and vertical sizes of the motion vector are each １ ／. The motion vector converted by the vector value conversion circuit 18 so that the size in the horizontal direction and the size in the vertical direction are each halved is stored in the first reference image memory 11.
And it is sent to the second reference image memory 12 as a control signal for controlling the cutout position of the reference image.

The variable length decoder 1 decodes a variable length code of a transform coefficient. The inverse quantizer 2 inversely quantizes the transform coefficients (quantized DCT coefficients) obtained from the variable length decoder 1 and converts them into DCT coefficients. The DCT coefficient obtained by the inverse quantizer 2 is sent to the IP zero replacement unit 4 or the B zero replacement unit 5 via the switch 3.

When the DCT coefficient obtained by the inverse quantizer 2 is for an I picture or a P picture, the switch 3 performs an inverse operation so that the DCT coefficient is sent to the IP zero replacement processing unit 4. When the DCT coefficient obtained by the quantizer 2 is for a B picture, the CPU 20 controls the DCT coefficient so that the DCT coefficient is sent to the B zero replacement processing unit 5.

As shown in FIG. 2A, the IP zero replacement processing unit 4 converts the DCT coefficient sequence generated by the inverse quantizer 2 into 8 (the number of pixels in the horizontal direction) × 8 (the number of pixels in the vertical direction). 8 × 8 DCT coefficients F (u, v) corresponding to sub-block units of
(Where u = 0, 1,... 7, v = 0, 1,... 7), and as shown in FIG. 2B, of the DCT coefficients for each sub-block, the high horizontal frequency Area part D
Replace the CT coefficient with 0. In this example, the DCT coefficients in the region where the horizontal frequency u is 4 or more are replaced with 0.

As shown in FIG. 3A, the zero-substitution processing unit 5 for B converts the DCT coefficient sequence generated by the
8 × 8 DCT coefficients F (u, v) corresponding to (horizontal pixel count) × 8 (vertical pixel count) subblock units
(Where u = 0, 1,... 7, v = 0, 1,... 7), and as shown in FIG. 3B, of the DCT coefficients of each sub-block, the high horizontal frequency The DCT coefficients of the band portion and the high frequency portion of the vertical frequency are replaced with 0.
In this example, the DCT coefficients in the region where the horizontal frequency u is 4 or more and the region where the vertical frequency v is 4 or more are replaced with 0.

The inverse DCT circuit 6 applies the 8 × 8 inverse DCT coefficient to the 8 × 8 DCT coefficients generated by the IP zero substitution processing unit 4 or the B zero substitution processing unit 5 based on the above equation (2). D
By performing CT, data f (i, j) (where, the number of data is 8 (the number of pixels in the horizontal direction) × 8 (the number of pixels in the vertical direction)) as shown in FIG. i = 0,
1,... 7, j = 0, 1,.

Further, based on the image data corresponding to the four sub-block units constituting one macro block obtained in this way, the reproduced image data or prediction error data of one 16 × 16 macro block unit is obtained. Generate.

The 16 × generated by the inverse DCT circuit 6
The reference image data corresponding to the macroblock type is added to the 16 macroblock-based prediction error data by the adder 7 to generate reproduced image data.
The reference image data is sent to the adder 7 via the switch 16. However, if the image data output from the inverse DCT circuit 6 is reproduced image data for the intra-frame prediction code, the reference image data is not added.

The reproduced image data in 16 × 16 macroblock units obtained by the inverse DCT circuit 6 or the adder 7 is sent to the thinning circuit 8. The thinning-out circuit 8 thins out the received 16 × 16 macroblock unit reproduced image data in the horizontal and vertical directions by １ ／ in each of the horizontal and vertical directions, thereby reducing the 16 × 16 macroblock unit reproduced image data in the horizontal direction. Then, the image data is converted into 8 × 8 macroblock-unit reproduced image data in which the vertical direction is compressed to １ ／. Therefore, the amount of image data in macroblock units obtained by the thinning circuit 8 is の of the amount of image data in macroblock units of the original image.

In the reproduced image data in units of 16 × 16 macroblocks obtained by the inverse DCT circuit 6 or the adder 7, the horizontal lines (shown by solid lines) and the even lines of the odd fields as shown in FIG. Since the horizontal lines of the field (indicated by the dashed lines) alternate in the vertical direction,
When thinning in the vertical direction is performed to include the horizontal lines of the odd field and the horizontal lines of the even field, the horizontal line 2 is used as shown in FIG.
Thinning is performed on a per-book basis.

If the reproduced image data in macroblock units obtained by the thinning circuit 8 is reproduced image data for a B picture, the reproduced image data is sent to the switch 9.

When the reproduced image data in units of macroblocks obtained by the thinning circuit 8 is reproduced image data for an I picture or a P picture, the reproduced image data is transmitted via the switch 10 to the first reference image. It is stored in the memory 11 or the second reference image memory 12. First reference image memory 11 or second reference image memory 1
The amount of image data stored in 2 becomes 1/4 of the conventional amount. The switch 10 is controlled by the CPU 20.

The first interpolation circuit 13 performs horizontal and vertical interpolation on the reference image data in 8 × 8 macroblock units read from the first reference image memory 11, that is, The horizontal and vertical lines thinned out by the thinning circuit 8 are interpolated to generate reference image data of 16 × 16 macroblock units.

The second interpolation circuit 14 performs interpolation in the horizontal and vertical directions on the reference image data read from the second reference image memory 12 in units of 8 × 8 macroblocks. The horizontal and vertical lines thinned out by the thinning circuit 8 are interpolated to generate reference image data of 16 × 16 macroblock units.

The averaging section 15 averages the image data read out from the first interpolation circuit 13 and the second interpolation circuit 14 to obtain a 16 × 1 image data used for the interpolative inter-frame predictive coding.
6 is generated for each macroblock.

The switch 16 is controlled by the CPU 20 as follows. If the data output from the inverse DCT circuit 6 is reproduced image data for intra-frame prediction coding, the common terminal of the switch 16 is switched to the ground terminal.

When the data output from the inverse DCT circuit 6 is prediction error data for a forward inter-frame prediction code or prediction error data for a backward inter-frame prediction code, the common terminal of the switch 16 1
Switching is performed to select either a terminal to which reference image data from the interpolation circuit 13 is sent or a terminal to which reference image data from the second interpolation circuit 14 is sent.

If the data output from the inverse DCT circuit 6 is prediction error data for an interpolative inter-frame prediction code, the common terminal of the switch 16 selects the terminal to which the output of the averaging unit 15 is sent. Is switched to.

When a reference image is read from the reference image memories 11 and 12, the vector value conversion circuit 1
8, the cutout position is controlled based on the motion vector. The reason why the horizontal and vertical magnitudes of the motion vector are converted to に よ っ て by the vector value conversion circuit 18 is that the motion vector is converted from the thinning circuit 8 to the reference image memory 1.
This is because the image data in units of macroblocks sent to 1 and 12 are compressed in half in the horizontal and vertical directions, respectively.

The switch 9 is connected between the thinning circuit 8 and the switch 9
The reproduced image data for the B picture, the reproduced image data for the I picture or the P picture stored in the reference image memory 11, and the reference image memory 12
Is controlled by the CPU 20 so that the reproduced image data for the I picture or the P picture stored in the image data is output in the same order as the order of the original images. The image data output from the switch 9 is format-converted by the format conversion circuit 19 so as to correspond to the number of horizontal and vertical scanning lines of the monitor device, and then sent to the monitor device.

According to the above embodiment, the memory 11 for the first reference image and the memory 12 for the second reference image can use one-fourth their conventional capacity.

Also, in the above embodiment, a part of the 8 × 8 transform coefficients for each sub-block obtained from the inverse quantizer 2 by the IP zero replacement processing unit 4 and the B zero replacement processing unit 5. Has been replaced with 0. Therefore, the inverse DC
The amount of calculation by the T circuit 6 is reduced.

By the way, in the above embodiment, the IP which processes the DCT coefficient for the I picture or the P picture is
In the zero-substitution processor 4, the DCT for each sub-block is
Of the coefficients, the DCT coefficient in the high frequency portion of the horizontal frequency is 0.
And the zero replacement processing unit 5 for B that processes the DCT coefficient for the B picture
Of the T coefficients, the DCT coefficients of the high frequency portion of the horizontal frequency and the high frequency portion of the vertical frequency are replaced with 0.

More specifically, the IP zero-substitution processing unit 4 replaces DCT coefficients in a region where the horizontal frequency u is 4 or more with 0 among DCT coefficients in 8 × 8 sub-block units, In the zero-substitution processing unit 5, DCT coefficients of a region where the horizontal frequency u is 4 or more and a region where the vertical frequency v is 4 or more among the 8 × 8 sub-block DCT coefficients are used.
The coefficient has been replaced by zero. That is, a part of the DCT coefficients is replaced with 0 so that the accuracy of the inverse DCT for the DCT coefficient for the I picture or the P picture is higher than the accuracy of the inverse DCT for the DCT coefficient for the B picture.

The reason will be described. As shown in FIG. 3, of the DCT coefficients of each sub-block, the DCT of the high frequency portion of the horizontal frequency and the high frequency portion of the vertical frequency
If the inverse DCT is performed after the coefficient is replaced with 0, the reproduction of an image including the high frequency portion of the horizontal frequency and the high frequency component of the vertical frequency becomes insufficient. However, when displaying an image at a resolution lower than the resolution of the original image, even if the reproduction of the image including the high-frequency component of the horizontal frequency and the high-frequency component of the vertical frequency is insufficient, there is not much problem. .

However, in the decoding of the MPEG system, the next image may be generated by referring to the decoded image. Therefore, if the reproduction of the reference image is insufficient, the reference The image quality of the image generated using the image is further reduced. Further, when the obtained image is used as a reference image, there is a problem that the image quality of the reproduced image is further reduced. In particular, when the image to be decoded is an interlaced image, a large amount of high frequency components in the vertical frequency is included, so that the image quality may be significantly reduced.

Therefore, in the above embodiment, as shown in FIG. 2, the I picture or the P picture to be referred to for decoding another picture is, as shown in FIG. Decoding is performed using not only the low-frequency part of the frequency but also the DCT coefficient of the high-frequency part of the vertical frequency component,
As shown in FIG. 3, for a B picture that is not referred to for decoding another image, decoding is performed using DCT coefficients of only the low-frequency part of the vertical frequency among the low-frequency parts of the horizontal frequency. That is to do.

In the case of an I picture or a P picture, 4 × 8 inverse DCT is performed after removing a DCT coefficient in a high frequency portion of a horizontal frequency from DCT coefficients of each sub block. The 4 × 4 inverse DCT may be performed after removing the DCT coefficients of both the high frequency part of the horizontal frequency and the high frequency part of the vertical frequency among the DCT coefficients of each sub block.

[0065]

According to the present invention, there is provided a moving picture decoding method suitable for obtaining a reproduced picture having a lower resolution than the resolution of the original picture and capable of reducing the amount of calculation.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an MPEG decoder.

FIG. 2 is a schematic diagram showing a DCT coefficient after a DCT coefficient in a high frequency portion of a horizontal frequency is replaced with 0 by an IP zero replacement unit and data after being inversely transformed by an inverse DCT circuit; is there.

FIG. 3 shows the DCT coefficients after the DCT coefficients of the high-frequency portion of the horizontal frequency and the high-frequency portion of the vertical frequency have been replaced with 0 by the zero-substitution processing unit for B, and after being inversely transformed by the inverse DCT circuit. It is a schematic diagram which shows the data of.

FIG. 4 is a schematic diagram for explaining a vertical thinning process performed by a thinning circuit.

FIG. 5 is a block diagram showing a configuration of a conventional MPEG decoder.

FIG. 6 is a schematic diagram for explaining DCT performed by an MPEG encoder and inverse DCT performed by a conventional MPEG decoder.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 variable length decoder 2 inverse quantizer 4 zero substitution processing unit for IP 5 zero substitution processing unit for B 6 inverse DCT circuit 7 adder 8 thinning circuit 11 memory for first reference image 12 memory for second reference image 13 First Interpolation Circuit 14 Second Interpolation Circuit 15 Averaging Unit 17 Variable Length Decoder 18 Vector Value Conversion Circuit 3, 9, 10, 16 Switch 19 Format Conversion Circuit 20 CPU

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shinichi Matsuura 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (6)

[Claims] 1. A moving picture decoding method for decoding a signal that has been compression-encoded by the MPEG method, wherein accuracy of inverse DCT for a B picture is lower than accuracy of inverse DCT for an I picture or a P picture. Moving image decoding method. 2. A D-picture for an I-picture or a P-picture.
The DCT coefficient of the high frequency part of the horizontal frequency in the CT coefficient is set to 0.
To the B picture,
After the DCT coefficients of the high frequency portion of the horizontal frequency and the high frequency portion of the vertical frequency of the CT coefficients are replaced with 0, the inverse DCT is performed.
The moving picture decoding method according to claim 1, wherein the accuracy of the inverse DCT for the B picture is made lower than the accuracy of the inverse DCT for the I picture or the P picture by performing. 3. When encoding an original image, DCT is performed in block units having M pixels in the horizontal direction and N pixels in the vertical direction.
Assuming that the transform has been performed, the inverse DCT is performed after replacing the DCT coefficients in the MxN block unit DCT coefficients of the I picture or the P picture in the higher frequency range than M / 2 with 0, M × N for B picture
The horizontal frequency of the DCT coefficients in block units of M /
3. The moving picture decoding method according to claim 2, wherein the inverse DCT is performed after replacing DCT coefficients of a higher frequency portion than 2 and a vertical frequency portion higher than N / 2 with 0. 4. A D-picture for an I-picture or a P-picture
After removing the DCT coefficient in the high frequency portion of the horizontal frequency from the CT coefficients, inverse DCT is performed, and DCT for the B picture is performed.
By performing the inverse DCT after removing the DCT coefficients of the high-frequency part of the horizontal frequency and the high-frequency part of the vertical frequency of the coefficients, the precision of the inverse DCT for the B picture is reduced. 2. The moving picture decoding method according to claim 1, wherein the moving picture decoding rate is set lower. 5. At the time of encoding an original image, DCT is performed in units of blocks each having the number of horizontal images M and the number of vertical pixels N.
If the transform is performed, the inverse DCT is performed after removing the DCT coefficient of the portion where the horizontal frequency is higher than M / 2 among the M × N block unit DCT coefficients for the I picture or the P picture, and performing the B picture Of the DCT coefficients in block units of M × N with respect to D, where the horizontal frequency is higher than M / 2 and the vertical frequency is higher than N / 2.
5. The moving picture decoding method according to claim 4, wherein the inverse DCT is performed after removing the CT coefficients. 6. The moving picture decoding method according to claim 3, wherein M = N = 8.