JP3416505B2 - Video decoding method - Google Patents

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 suitable for decoding a signal compression-coded by the MPEG method to obtain a reproduced image having a resolution lower than that of an original image. The present invention relates to an image decoding method.

[0002]

2. Description of the Related Art An MPEG (Moving Picture Expert Group) system has been known as an image coding system 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 progressive scan (non-interlaced) images are handled, but M
With PEG2, not only progressive scanning images but also interlaced scanning images have come to be handled.

For these MPEG encodings, motion compensation prediction (temporal compression), DCT (spatial compression) and entropy encoding (variable length encoding) are adopted. MP
In EG encoding, first, predictive encoding in the time axis direction (frame predictive encoding in MPEG1, frame predictive encoding or field predictive encoding in MPEG2) is performed for each macroblock.

A macroblock has a Y signal (luminance signal) of 16 (horizontal pixel number) × 16 (vertical pixel number) and 8 (horizontal pixel number) × 8 (vertical pixel number). It is composed of a Cb signal (color difference signal) having a size and a Cr signal (color difference signal) having a size of 8 (the number of pixels in the horizontal direction) × 8 (the number of pixels in the vertical direction).

Here, for convenience of description, only the Y signal will be described. I picture corresponding to the predictive coding system,
There are three image types, P picture and B picture. In the following, frame predictive coding will be described as an example.

(1) I picture: This is a screen encoded only from the information in the frame and is generated without interframe prediction. All macroblock types in the I picture are in the frame. This is an intra-frame predictive coding in which only information is coded.

(2) P picture: This is a screen created by performing prediction from an I or P picture. Generally, the macroblock type in a P picture is an intraframe code that is coded using only intraframe information. Encoding and forward inter-frame predictive coding that is predicted from a past reproduced image.

(3) B picture: A picture that can be formed by bidirectional prediction, and generally includes the following macroblock types. a. Intra-frame predictive coding in which only intra-frame information is coded b. Forward inter-frame predictive coding for prediction from past reproduced images c. Backward inter-frame predictive coding for prediction from the future d. Interpolative Inter-frame Prediction Coding by Both Pre- and Post-Prediction Here, interpolative inter-frame prediction means averaging two predictions of forward prediction and backward prediction between corresponding pixels.

In the MPEG encoder, the image data of the original image is 16 (horizontal pixel number) × 16 (vertical pixel number)
It is divided into macroblock units of size. For a macroblock whose macroblock type is other than intraframe predictive coding, interframe prediction according to the macroblock type is performed, and prediction error data is generated.

Image data for each macroblock (when the macroblock type is intraframe predictive coding) or prediction error data (when the macroblock type is interframe 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 one type of orthogonal transformation, is performed on the image data of each sub-block based on Formula 1. That is, as shown in FIG. 6, 8 × 8
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 the block of size.

[0012]

[Equation 1]

In MPEG1, the DCT has a frame D.
Although only the CT mode is used, in the frame structure of MPEG2, it is possible to switch between the frame DCT mode and the field DCT mode in macroblock units. However, in the field structure of MPEG2, the field DC
Only in T mode.

In the frame DCT mode, a 16 × 16 macroblock is divided into four, and the upper left 8 × 8 block, the upper right 8 columns and 8 rows block, the lower left 8 × 8 block, and the lower right 8 × 8. 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 an 8 (horizontal direction pixel number) × 16 (vertical direction pixel number) block in the left half of a × 16 macroblock, and an 8 × 16 block in the left half 8 × 8 data group consisting of only even lines, 8 × 8 data group consisting of only odd lines in the right half 8 (horizontal pixel number) × 16 (vertical pixel number) block and right half 8 D for each data group of the 8 × 8 data group consisting of only even lines in the × 16 block
CT is performed.

The DCT coefficient obtained as described above is quantized to generate a quantized DCT coefficient. The quantized DCT coefficients are zigzag-scanned or alternate-scanned, arranged in one dimension, and coded by a variable-length encoder. The MPEG encoder outputs the variable-length code of the transform coefficient obtained by the variable-length encoder, the control information including the information indicating the macroblock type, and the variable-length code of the motion vector.

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

The variable length code of the transform coefficient is sent to the variable length decoder 101. Control signals including the macroblock type are sent to the CPU 110. The variable length code of the motion vector is sent to the variable length decoder 109 to be 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 the variable length code of the transform coefficient. The inverse quantizer 102 receives the transform coefficient (quantized DCT) obtained from the variable length decoder 101.
Coefficient) is inversely quantized and converted into a DCT coefficient.

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

[0021]

[Equation 2]

In the prediction error data in macroblock units generated by the inverse DCT circuit 103, reference image data corresponding to the macroblock type is added by the adder 104.
Are added to generate reproduced image data. The reference image data is added to the adder 104 via the switch 112.
Sent to. However, when the data output from the inverse DCT circuit 103 is the 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 B
If the reproduced image data is for a picture, the reproduced image data is sent to the switch 113.

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

The averaging unit 108 includes the memories 106 and 107.
The reproduced image data read from is averaged to generate reference image data used in the inter-frame predictive coding.

The switch 112 is controlled by the CPU 110 as follows. When the data output from the inverse DCT circuit 103 is the reproduced image data for the intraframe 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 the prediction error data for the forward inter-frame prediction code or the prediction error data for the backward inter-frame prediction code, the common terminal of the switch 112 is the first terminal. It is switched to select either the terminal to which the output of the 1-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 image is 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 the interpolative interframe prediction code, the common terminal of the switch 112 is the averaging unit 1.
It is switched to select the terminal to which the 08 output is sent.

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

[0030]

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

[0031]

According to a first aspect of the dynamic <br/> image decoding method according to the invention, in the moving picture decoding method for decoding a signal compressed and encoded by the MPEG system, the color difference
Of the high frequency part of the horizontal frequency of the DCT coefficient for the signal
After replacing the DCT coefficient with 0, inverse DCT is performed and the luminance signal is
Of the DCT coefficient for the signal
And the DCT coefficient in the high frequency part of the vertical frequency is replaced with 0.
It is characterized in that the inverse DCT is performed later .

When encoding the original image, horizontal pixels
DCT change in units of M blocks and N vertical pixels
If conversion is performed, M × N of the color difference signals
Of the DCT coefficients in block units, the horizontal frequency is M / 2
After replacing the DCT coefficient in the high frequency region with 0, the inverse DCT is
M × N blocks for the DCT coefficient of the luminance signal
Horizontal frequency of unit DCT coefficient is higher than M / 2
Part and DCT section of vertical frequency higher than N / 2
It is preferred to perform the inverse DCT after substituting the number with zero.
An example of M and N is M = N = 8.

Second video decoding method according to the present invention
Decodes signals compressed and encoded by the MPEG system
In the moving picture decoding method, the D
The DCT coefficient in the high frequency part of the horizontal frequency is excluded from the CT coefficient.
Then, the inverse DCT is performed and the DCT function for the luminance signal is performed.
High part of the horizontal frequency and high part of the vertical frequency of the number
Performing inverse DCT after removing the DCT coefficient in the region
Is characterized by.

When the original image is encoded, if DCT conversion is performed in a block unit in which the number of horizontal images is M and the number of vertical pixels is N, DCT coefficients in M × N block units for the color difference signals. of performs inverse DCT after the horizontal frequency to remove DCT coefficients of the high portion than M / 2, the horizontal frequency of the DCT coefficients of the block unit of M × N for DCT coefficients of the luminance signal is high than M / 2 of It is preferable to perform the inverse DCT after removing the DCT coefficients in the high frequency part and the high frequency part in which the vertical frequency is higher than N / 2 . M, N
For example, M = N = 8 can be cited.

[0035]

[0036]

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention applied to an MPEG decoder will be described below with reference to FIGS.

FIG. 1 shows the structure of the MPEG decoder.

The variable length code of the transform coefficient is sent to the variable length decoder 1. Control signals including the macroblock type are sent to the CPU 30. The variable length code of the motion vector is sent to the variable length decoder 23 to be decoded. The motion vector obtained by the variable length decoder 23 is sent to the vector value conversion circuit 24. Vector value conversion circuit 2
4 generates a control signal for controlling the cut-out position of the reference image in the first reference image memory 13 and the second reference image memory 14.

Specifically, the color difference signals Cb, Cr (hereinafter,
When it is not necessary to distinguish between Cb and Cr, these are collectively referred to as the C signal). When the reference image for the C signal is read, the vector value conversion circuit 24 determines that the magnitude of the motion vector in the horizontal direction is large. The motion vector is converted so as to be halved and output.

On the other hand, a luminance signal Y (hereinafter referred to as Y signal)
When the reference image for is read, the vector value conversion circuit 24 performs motion vector conversion so that the magnitudes of the motion vector in the horizontal direction and in the vertical direction are 1/2 and outputs the motion vector.

The variable length decoder 1 decodes the variable length code of the transform coefficient. The inverse quantizer 2 inversely quantizes the transform coefficient (quantized DCT coefficient) obtained from the variable length decoder 1 and transforms it into a DCT coefficient. The DCT coefficient obtained by the inverse quantizer 2 is sent to the Y zero substitution processing unit 4 or the C zero substitution processing unit 5 via the switch 3.

The switch 3 is provided with a switch 3 when the DCT coefficient obtained by the inverse quantizer 2 is for the Y signal.
When the DCT coefficient obtained by the inverse quantizer 2 is for the C signal so that the DCT coefficient is sent to the Y zero substitution processing section 4, the DCT coefficient is the C zero substitution processing section 5 Is controlled by the CPU 30.

As shown in FIG. 2 (a), the Y zero substitution processing section 4 converts the DCT coefficient sequence generated by the inverse quantizer 2 into eight.
8 × 8 DCT coefficient F (u, v) corresponding to a sub-block unit of (horizontal pixel number) × 8 (vertical pixel number)
(However, u = 0,1, ... 7, v = 0,1, ... 7), and as shown in FIG. 2B, the DCT coefficient of each sub-block unit has a higher horizontal frequency. The DCT coefficients of the band part and the high band part of the vertical frequency are replaced with zero.
In this example, the DCT coefficients of 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 C zero substitution processing unit 5 has a macroblock unit of 8 (horizontal pixel number) × 8 (vertical pixel number) generated by the inverse quantizer 2 (see FIG. 3A: C signal). Then, DCT coefficient F (u, v) of 8 × 8 is a macroblock unit (where u = 0, 1, ... 7, v = 0,
As shown in FIG. 3B, the DCT coefficients of the high frequency part of the horizontal frequency of the DCT coefficients of each sub-block are replaced with 0. In this example, the horizontal frequency u
The DCT coefficient in the region where is 4 or more is replaced with 0.

The inverse DCT circuit 6 includes a Y zero substitution processing section 4
Alternatively, an 8 × 8 inverse DC is calculated based on the above Equation 2 on the 8 × 8 number of DCT coefficients generated by the C zero substitution processing unit 5.
By applying T, the data f (i, j) having the data number of 8 (horizontal pixel number) × 8 (vertical pixel number) as shown in FIG. i = 0, 1,
, 7, j = 0, 1, ... 7) is generated.

When the coefficient subjected to the inverse DCT is the C signal, the reproduced image data or prediction error data in 8 × 8 macroblock units obtained by the inverse DCT is output as it is.

On the other hand, when the coefficient subjected to the inverse DCT is the Y signal, 16 × 16 based on the image data corresponding to the unit of four sub-blocks forming one macroblock obtained by the inverse DCT. Regenerated image data or prediction error data in units of one macroblock is generated and output.

Reference image data corresponding to the macroblock type is added to the prediction error data in macroblock units generated by the inverse DCT circuit 6 by the adder 7 to generate reproduced image data. The reference image data is sent to the adder 7 via the switch 22. However, when the image data output from the inverse DCT circuit 6 is the reproduced image data for the intraframe prediction code,
Reference image data is not added.

Reproduced image data in 16 × 16 macroblock units for the Y signal obtained by the inverse DCT circuit 6 or the adder 7 is sent to the Y thinning circuit 9 through the switch 8. The Y thinning circuit 9 thins out the reproduced image data in units of 16 × 16 macroblocks of the transmitted Y signal in the horizontal and vertical directions to 1/2, thereby reproducing in units of 16 × 16 macroblocks. The image data is converted into reproduced image data in units of 8 × 8 macroblocks, each of which is compressed to ½ in the horizontal and vertical directions. Therefore, the image data amount in macroblock units obtained by the Y thinning circuit 9 is ¼ of the image data amount in macroblock units of the original image.

Reproduced image data in 8 × 8 macroblock units for the C signal obtained by the inverse DCT circuit 6 or the adder 7 is passed through the switch 8 to the C thinning circuit 10
Sent to. The thinning-out circuit 10 for C thins out the reproduced image data in units of 8 × 8 macroblocks of the transmitted C signal to 1/2 in the horizontal direction, thereby reproducing the reproduced image data in units of 8 × 8 macroblocks. , Horizontal is 1/2
It is converted into reproduced image data in units of 4 × 8 macroblocks compressed into. Therefore, the amount of image data in macroblock units obtained by the C thinning circuit 10 is 1/2 of the amount of image data in macroblock units of the original image.

In the reproduced image data in macro block units obtained by the inverse DCT circuit 6 or the adder 7, as shown in FIG. 4A, the horizontal lines of odd fields (shown by solid lines) and the even fields are shown. Since horizontal lines (shown by broken lines) alternately appear in the vertical direction, when performing thinning in the vertical direction in the Y thinning circuit 9,
In order to include the horizontal lines of odd fields and the horizontal lines of even fields, thinning is performed in units of two horizontal lines as shown in FIG. 4B.

When the reproduced image data in macro block units obtained by the Y thinning circuit 9 or the C thinning circuit 10 is the reproduced image data for the B picture, the reproduced image data is sent to the switch 11. To be

When the reproduced image data in macro block units obtained by the Y thinning circuit 9 or the C thinning circuit 10 is the reproduced image data for the I picture or P picture, the reproduced image data is switched. 12
And is stored in the first reference image memory 13 or the second reference image memory 14 via. The switch 12 is the CPU 3
Controlled by 0.

The image for the Y signal is the first as the reference image.
When read from the reference image memory 13, the image corresponding to the read Y signal is sent to the first Y interpolation circuit 16 via the switch 15. The first Y interpolation circuit 16 reads the Y read from the first reference image memory 13.
The reference image data in 8 × 8 macroblock units for the signal is interpolated in the horizontal and vertical directions, that is, the horizontal and vertical lines thinned by the Y thinning circuit 9 are interpolated, The reference image data in units of macroblocks of × 16 is generated.

The image for the Y signal is the second as the reference image.
When read from the reference image memory 14, the image corresponding to the read Y signal is sent to the second Y interpolation circuit 19 via the switch 18. The second Y interpolation circuit 19 reads the Y read from the second reference image memory 14.
The reference image data in 8 × 8 macroblock units for the signal is interpolated in the horizontal and vertical directions, that is, the horizontal and vertical lines thinned by the Y thinning circuit 9 are interpolated, The reference image data in units of macroblocks of × 16 is generated.

The image for the C signal is the first as the reference image.
When read from the reference image memory 13, the image corresponding to the read C signal is sent to the first C interpolation circuit 17 via the switch 15. The first C interpolation circuit 17 reads the C read from the first reference image memory 13.
Interpolation in the horizontal direction is performed on the reference image data in 4 × 8 macroblock units for the signal, that is, the vertical line thinned by the C thinning circuit 10 is interpolated,
Reference image data is generated in units of 8 × 8 macroblocks.

The image for the C signal is the second as the reference image.
When read from the reference image memory 14, the image corresponding to the read C signal is sent to the second C interpolation circuit 20 via the switch 18. The second C interpolation circuit 20 reads the C read from the second reference image memory 14.
Interpolation in the horizontal direction is performed on the reference image data in 4 × 8 macroblock units for the signal, that is, the vertical line thinned by the C thinning circuit 10 is interpolated,
Reference image data is generated in units of 8 × 8 macroblocks. The switches 15 and 18 are controlled by the CPU 30.

The averaging unit 21 includes a first Y interpolation circuit 16
And the image data obtained from the second Y interpolation circuit 19 or the image data obtained from the first C interpolation circuit 17 and the second C interpolation circuit 20 are averaged to obtain an interpolation Reference image data for each macroblock used for interframe predictive coding is generated.

The switch 22 is controlled by the CPU 30 as follows. When the data output from the inverse DCT circuit 6 is reproduced image data for intraframe predictive coding, the common terminal of the switch 22 is switched to the ground terminal.

When the data output from the inverse DCT circuit 6 is the prediction error data for the forward interframe prediction code or the prediction error data for the backward interframe prediction code, the common terminal of the switch 22 is the first terminal. 1
To the terminal to which the reference image data from the Y interpolation circuit 16 or the first C interpolation circuit 17 is sent, or the reference from the second Y interpolation circuit 19 or the second C interpolation circuit 20. It is switched to select either one of the terminals to which the image data is sent.

When the data output from the inverse DCT circuit 6 is the prediction error data for the interpolated interframe prediction code, the common terminal of the switch 22 selects the terminal to which the output of the averaging unit 21 is sent. Is switched to.

When the reference image is read from the reference image memories 13 and 14, the vector value conversion circuit 2 is used.
The cutout position is controlled based on the motion vector from 4.

When the reference image for the C signal is read, the horizontal value of the motion vector is converted to ½ by the vector value conversion circuit 24 because the thinning circuit 10 for C references the reference image. This is because the image data in macro block units sent to the memory 13 and 14 are compressed to 1/2 in the horizontal direction.

Further, when the reference image for the Y signal is read, the horizontal and vertical magnitudes of the motion vector are converted to 1/2 by the vector value conversion circuit 24 because the Y thinning circuit. Reference image memory 1 from 9
This is because the image data in units of macro blocks sent to Nos. 3 and 14 has been compressed to 1/2 in the horizontal and vertical directions.

The switch 11 is a thinning circuit for Y 9 or C.
Reproduced image data for B picture sent from the thinning-out circuit 10 to the switch 11, I picture stored in the reference image memory 13 or reproduced image data for P picture, I picture stored in the reference image memory 14 Alternatively, the CPU 30 controls the reproduced image data for the P picture to be output in the same order as the original image. The image data output from the switch 11 is format-converted by the format conversion circuit 25 so as to correspond to the number of horizontal and vertical scanning lines of the monitor device, and then sent to the monitor device.

In the above embodiment, a part of the 8 × 8 transform coefficient obtained from the inverse quantizer 2 is replaced with 0 by the Y zero substitution processor 4 and the C zero substitution processor 5. There is. Therefore, the amount of calculation by the inverse DCT circuit 6 is reduced.

By the way, in the above embodiment, in the C zero substitution processing section 5 for processing the DCT coefficient for the C signal, the high frequency part of the horizontal frequency of the DCT coefficient of each 8 × 8 macro block is processed. In the Y zero substitution processing unit 4 in which the DCT coefficient is replaced by 0 and the DCT coefficient for the Y signal is processed, the high frequency part of the horizontal frequency and the vertical frequency of the DCT coefficient of each 8 × 8 sub-block are processed. The DCT coefficient in the high frequency part is replaced with 0.

Specifically, in the C zero substitution processing section 5,
Of the 8 × 8 macroblock DCT coefficients, the DCT coefficient in the region where the horizontal frequency u is 4 or more is replaced with 0, and the Y zero replacement processing unit 4 uses the 8 × 8 subblock DCT coefficient. Among them, the DCT coefficients of 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. That is, DC for C signal
The accuracy of the inverse DCT for the T coefficient is
D to be higher than the accuracy of the inverse DCT for the T coefficient
A part of the CT coefficient is replaced with 0.

The reason for this will be described. As shown in FIG. 2, the DC of the high frequency part of the horizontal frequency and the high frequency part of the vertical frequency of the DCT coefficient of 8 × 8 for the Y signal.
If the inverse DCT is performed after the T coefficient is replaced with 0, the reproduction of an image including the high frequency part of the horizontal frequency and the high frequency component of the vertical frequency becomes insufficient. However, since the reproduction deterioration of the Y signal only affects the lightness and darkness rather than the color tone, when displaying an image at a resolution lower than the resolution of the original image, the high frequency component of the horizontal frequency of the Y signal and the vertical frequency Even if the reproduction of the image including the high frequency component is insufficient, it does not cause a problem so much.

However, since the reproduction deterioration of the C signal affects the color tone, even when the image is displayed at a resolution lower than the resolution of the original image, the high frequency component of the horizontal frequency of the C signal and the vertical frequency are generated. If reproduction of an image including the high frequency component of is insufficient, there is a problem that the reproduction deterioration is visually noticeable. In particular, when the image to be decoded is an interlaced image, there is a time lag between the odd field and the even field, and a high frequency component in the vertical direction is likely to occur due to the motion, so that the DCT coefficient for the C signal is If the inverse DCT is performed after substituting the high frequency component of the vertical frequency with 0, there is a problem that the image quality is significantly deteriorated.

Therefore, in the above-described embodiment, for the C signal, which is greatly related to the color tone where the influence of the image deterioration is conspicuous, as shown in FIG.
Decoding is performed using not only the low frequency part of the vertical frequency but also the DCT coefficient of the high frequency part of the vertical frequency component, and FIG. As shown, of the low-frequency part of the horizontal frequency,
The decoding is performed using the DCT coefficient of only the low frequency part of the vertical frequency.

With respect to the C signal, D of the high frequency part of the horizontal frequency in the DCT coefficient of each sub-block unit
After removing the CT coefficient, 4 × 8 inverse DCT is performed, and for the Y signal, the DCT coefficients of both the high-frequency part of the horizontal frequency and the high-frequency part of the vertical frequency of the DCT coefficient of each sub-block unit are calculated. The 4 × 4 inverse DCT may be performed after the removal.

[0074]

According to the present invention, it is possible to obtain a moving image decoding method suitable for obtaining a reproduced image having a resolution lower than that of an original image and capable of reducing the amount of calculation.

[Brief description of drawings]

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

FIG. 2 shows DCT coefficients after the DCT coefficients of the high frequency part of the horizontal frequency and the high frequency part of the vertical frequency have been replaced by 0 by the Y zero replacement processing section, and after being inversely transformed by the inverse DCT circuit. It is a schematic diagram which shows the data of.

FIG. 3 is a schematic diagram showing the DCT coefficient after the DCT coefficient in the high frequency part of the horizontal frequency is replaced by 0 by the zero replacement processing unit for C, and the data after being inversely transformed by the inverse DCT circuit. is there.

FIG. 4 is a schematic diagram for explaining vertical thinning processing by a Y 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]

1 Variable length decoder 2 Inverse quantizer 4 Y zero replacement processor Zero replacement processing unit for 5 C 6 Inverse DCT circuit 7 adder 9 Y thinning circuit Thinning circuit for 10 C 13 First Reference Image Memory 14 Second reference image memory 16 First Y Interpolation Circuit 17 First C Interpolation Circuit 19 Second Y interpolation circuit 20 Second C interpolation circuit 21 Averaging unit 23 Variable Length Decoder 24 Vector value conversion circuit 3,8,11,12,15,18,22 switch 25 format conversion circuit 30 CPU

Front Page Continuation (72) Inventor Shinichi Matsuura 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-4-211575 (JP, A) JP-A-5 -30536 (JP, A) JP 6-22291 (JP, A) JP 7-160865 (JP, A) JP 9-200772 (JP, A) JP 9-215008 (JP, A) ) JP-A-9-247673 (JP, A) JP-A-11-243549 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N 11/04 H04N 7/30 H04N 7 / 32

Claims (5)

(57) [Claims] 1. A moving picture decoding method for decoding a signal compressed and encoded by the MPEG method, wherein a high frequency part of a horizontal frequency of DCT coefficients for a color difference signal.
Inverse DCT is performed after replacing the DCT coefficient for
High frequency part of the DCT coefficient for the degree signal
Replaces the DCT coefficient in the high frequency part of minute and vertical frequency with 0
A moving picture decoding method, characterized in that the inverse DCT is performed after that . 2. A horizontal image when encoding an original image.
DCT in block units with a prime number M and vertical pixel number N
If conversion is performed, M × N for the color difference signal
Of the DCT coefficients of each block of the horizontal frequency is M / 2
Inverse DCT after replacing the DCT coefficient in the higher frequency band with 0
Block of M × N for the DCT coefficient of the luminance signal.
The horizontal frequency of DCT coefficient is higher than M / 2.
DCT in the high frequency part and the vertical frequency higher than N / 2
It is characterized in that the inverse DCT is performed after replacing the coefficient with 0.
The moving picture decoding method according to claim 1 . 3. Compressed and encoded by the MPEG system
In a moving picture decoding method for decoding a signal, a high frequency part of a horizontal frequency of DCT coefficients for a color difference signal.
Inverse DCT is performed after removing the DCT coefficient for
Of the DCT coefficient for the signal
And after removing the DCT coefficient in the high frequency part of the vertical frequency
A moving picture decoding method characterized by performing inverse DCT . 4. A horizontal image when encoding an original image.
DCT in block units with M images and N vertical pixels
If conversion is performed, M × N for the color difference signal
Of the DCT coefficients of each block of the horizontal frequency is M / 2
Inverse DCT is performed after removing the DCT coefficient in the higher range.
A block of M × N for the DCT coefficient of the luminance signal
Horizontal frequency of DCT coefficient of higher order is higher than M / 2
Minute and vertical frequency DCT coefficient higher than N / 2
The inverse DCT is performed after removing the.
4. The moving picture decoding method according to item 3 . 5. The method according to claim 5, wherein M = N = 8.
Item 5. The moving image decoding method according to any one of items 2 and 4 .