JPH11243549A - Dynamic image decoding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the image quantity of a reproduced image with respect to the vertical thinning rate of m/8 (m is an odd number) by performing vertical thinning to the reproduced image of macro-block units, so as to convert 16 horizontal lines into 2m horizontal lines in the reproduced image after thinning. SOLUTION: When an original image is an interlaced image with the vertical thinning rate set at m/8 (m is an odd number), a reproduced image is obtained for each macro-block units, having 16 vertical direction pixels based on the image where inverse DCT has been applied to the luminance signals. This reproduced image undergoes vertical thinning, so that 16 horizontal lines are converted into 2m horizontal lines in a reproduced image after thinning and also that the number of horizontal lines of odd fields are equal to the number of horizontal lines of even fields in the reproduced image the after thinning. That is, the thinning circuits 7 and 8 perform the vertical thinning with respect to a reproduced image that is obtained by an inverse DCT circuit 4 or an adder 5, with, for example a thinning rate of 3/8.

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, prediction encoding in the time axis direction (frame prediction encoding in MPEG1 and frame prediction encoding or field prediction encoding in MPEG2) is performed for each macroblock.

In the case of the 4: 2: 0 format, a macroblock has a Y signal (luminance signal) having a size of 16 (the number of pixels in the horizontal direction) × 16 (the number of pixels in the vertical direction) and 8 (the number of pixels in the horizontal direction). It consists of a Cb signal (color difference signal) having a size of × 8 (the number of pixels in the vertical direction) 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 explanation, only the Y signal will be described. I picture corresponding to the predictive coding method,
There are three image types, P picture and B picture. 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, a 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 formed 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.

In the MPEG encoder, the image data of the original image is 16 (the number of pixels in the horizontal direction) × 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 (when the macroblock type is intra-frame prediction coding) or prediction error data (when the macroblock type is inter-frame prediction coding) for each macroblock unit 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.

[0012]

(Equation 1)

In MPEG1, a 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 parts, an upper left 8 × 8 block, an upper right eight column and eight row block, a lower left 8 × 8 block, and a lower right 8 × 8 block. 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.

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. 7 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. 8, 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.

[0021]

(Equation 2)

The prediction error data in macroblock units generated 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.

If 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.

[0030]

When a reproduced image having a lower resolution than that of the original image is obtained, the first DCT coefficient is used to perform the inverse DCT on the basis of the obtained image. (1) generating a first reproduced image, performing at least the vertical direction thinning out of the horizontal thinning out and the vertical direction thinning out of the first reproduced image, and generating a second reproduced image having a lower resolution than the original image. It is possible to do.

In such a case, when the thinning rate in the vertical direction is m / 8 and m is an even number such as 2, 4, 6, the first reproduced image is divided into 8 × 8 blocks. Even if vertical thinning is performed, the horizontal lines of the odd fields and the horizontal lines of the even fields in the second reproduced image after the thinning can be equalized by m / 2.

However, the thinning rate in the vertical direction is m /
8, when m is an odd number such as 1, 3, 5, and 7, when the first reproduced image is vertically decimated in units of 8 × 8 blocks, the second reproduced image in the decimated second reproduced image is obtained. The number of horizontal lines in odd fields and the number of horizontal lines in even fields cannot be equalized. For example, if the thinning rate in the vertical direction is 3/8, the second
Assuming that the number of horizontal lines in the odd field in the reproduced image is 2, the number of horizontal lines in the even field in the second reproduced image after thinning is 1 and there is a problem that the image quality of the reproduced image is deteriorated.

According to the present invention, a first reproduced image is generated based on an image obtained by performing inverse DCT in units of 8 × 8 blocks using only a part of the DCT coefficients, and In the moving picture decoding method of performing at least the vertical thinning out of the horizontal thinning and the vertical thinning out of the reproduced image to generate a second reproduced image having a low resolution with respect to the original image, the vertical thinning is performed. The rate is m / 8, m
It is an object of the present invention to provide a moving picture decoding method capable of improving the quality of a reproduced picture when is odd.

[0034]

SUMMARY OF THE INVENTION A moving picture decoding method according to the present invention is a moving picture decoding method for decoding a signal which has been compression-encoded by the MPEG method, wherein only a part of DCT coefficients is used. A first reproduced image is generated based on the image obtained by performing the inverse DCT using the first reproduced image, and at least the vertical direction thinning out of the horizontal direction thinning and the vertical direction thinning is performed on the first reproduced image, In the moving picture decoding method for generating a second reproduced image having a lower resolution than the original image, if the original image is an interlaced image, the vertical thinning rate is m / 8, and m is an odd number, For the luminance signal, a first reproduced image in a macroblock unit having 16 pixels in the vertical direction is generated based on an image obtained by performing inverse DCT, and a first reproduced image in a macrobook unit is generated. And 1 The second book horizontal line after the thinning
In the vertical direction so that the number of horizontal lines in the odd-numbered field is equal to the number of horizontal lines in the even-numbered field in the thinned-out second reproduced image. Is performed.

The first reproduced image may be generated based on an image obtained by performing an inverse DCT after removing a part of the DCT coefficient, or by performing an inverse DT after replacing a part of the DCT coefficient with 0.
It may be generated based on an image obtained by performing CT.

[0036]

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 macro block type is sent to the CPU 30. The variable length code of the motion vector is sent to the variable length decoder 21 and decoded. The motion vector obtained by the variable length decoder 21 is sent to a vector value conversion circuit 22.

The vector value conversion circuit 22 converts the motion vector so that the horizontal size of the motion vector becomes １ ／ and the vertical size of the motion vector becomes ／. Output. The output of the vector value conversion circuit 22 is sent to the first reference image memory 11 and the second reference image memory 12 as a control signal for controlling the cutout position of the reference image.

The motion vector is converted by the vector value conversion circuit 22 so that the horizontal size of the motion vector becomes １ ／ and the vertical size of the motion vector becomes ／. The reasons are as follows.

As will be described later, 4 × 8
Is performed by the inverse DCT circuit 4 or the adder 5 so that the horizontal direction of the original image is １ ／.
Thus, a first reproduced image is obtained. Also, the inverse DC
With respect to the first reproduced image obtained by the T circuit 4 or the adder 5, the decimation circuits 3 and 8 decimate the signal by 3/8.
Is performed, the second reproduced image is compressed in which the horizontal direction of the original image is reduced to に 対 し て and the vertical direction is compressed to ／ of the original image. The second reproduced image generated in this manner is stored in the first reference image memory 1.
This is because they are stored in the first and second reference image memories 12.

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. As shown in FIG. 2A, the horizontal high-frequency coefficient removal circuit (coefficient reduction circuit) 3 converts the DCT coefficient sequence generated by the inverse quantizer 2 into 8 (number of pixels in the horizontal direction) × 8 (pixels in the vertical direction). ) Of 8 × 8 DCT coefficients F (u, v) (where u =
0, 1,... 7, v = 0, 1,... 7), and the DCT coefficient of the high frequency portion of the horizontal frequency of each sub-block is removed, and as shown in FIG. DCT coefficients F in the number of frequency directions u) × 8 (vertical frequency direction v)
(U, v) (where u = 0, 1,... 3, v = 0, 1,
... 7) is converted.

The inverse DCT circuit 4 applies 4 × 8 inverse DCT as shown in Expression 3 to the 4 × 8 DCT coefficients generated by the horizontal high-frequency coefficient removal circuit 3 and obtains the result shown in FIG. ), The original data in units of sub-blocks is 1 /
Data f (i, j) consisting of 4 (the number of pixels in the horizontal direction) × 8 (the number of pixels in the vertical direction) compressed into 2 (where i = 0, 1,... 3, j = 0, 1, 1) .. 7) are generated.

[0044]

(Equation 3)

When the coefficient subjected to the inverse DCT is a C signal, the inverse DCT circuit 4 reproduces 4 (the number of horizontal pixels) × 8 (the number of vertical pixels) macroblock units obtained by the inverse DCT. The image data or the prediction error data is output as it is.

On the other hand, when the coefficient subjected to inverse DCT is a Y signal, the inverse DCT circuit 4 outputs image data corresponding to four sub-block units constituting one macroblock obtained by inverse DCT. , And generates and outputs 8 (the number of horizontal pixels) × 16 (the number of vertical pixels) reproduced image data or prediction error data in one macroblock unit.

The adder 5 adds reference image data corresponding to the macroblock type to the prediction error data in macroblock units generated by the inverse DCT circuit 4 to generate reproduced image data. The reference image data is sent to the adder 5 via the switch 20. However, when the image data output from the inverse DCT circuit 4 is reproduced image data for the intra-frame prediction code,
No reference image data is added.

The first reproduced image data in 8 × 16 macroblock units for the Y signal obtained by the inverse DCT circuit 4 or the adder 5 is sent to the Y thinning circuit 7 via the switch 6. The thinning circuit for Y 7
The first reproduced image data corresponding to the signal is thinned down to 3/8 in the vertical direction in units of macro blocks, so that the vertical direction of the first reproduced image data is compressed to 3/8. The second reproduced image data is generated for each macroblock (the number of pixels). Therefore, the image data amount in macroblock units obtained by the Y thinning circuit 7 is 3/3 of the image data amount in macroblock units of the original image.
It becomes 16.

The first reproduced image data in 4 × 8 macroblock units for the C signal obtained by the inverse DCT circuit 4 or the adder 5 is sent to the C thinning circuit 8 via the switch 6. The C thinning circuit 8 thins the first reproduced image data for the transmitted C signal in the vertical direction by 3/8 in macroblock units, thereby reducing the vertical direction of the first reproduced image data to 3/8. The compressed second reproduction image data is generated in 4 × 3 macroblock units. Accordingly, the image data amount in macroblock units obtained by the C thinning circuit 8 is 3/16 of the image data amount in macroblock units of the original image.

The details of the vertical thinning by the Y thinning circuit 7 and the details of the vertical thinning by the C thinning circuit 8 will be described later.

When the second reproduced image data in macroblock units obtained by the Y thinning circuit 7 or the C thinning circuit 8 is reproduced image data for a B picture, the reproduced image data is switched. 9

If the second reproduced image data in macroblock units obtained by the Y thinning circuit 7 or the C thinning circuit 8 is reproduced image data for an I picture or a P picture, the reproduced image Data is switch 1
0 is stored in the first reference image memory 11 or the second reference image memory 12. The switch 10 is a CPU
30.

The image corresponding to the Y signal is the first as the reference image.
When the image is read from the reference image memory 11, the image corresponding to the read Y signal is sent to the first Y interpolation circuit 14 via the switch 13. The first Y interpolation circuit 14 reads the Y image read from the first reference image memory 11.
The vertical interpolation is performed on the reference image data of 8 × 6 macroblock units for the signal, that is, the horizontal lines thinned out by the Y thinning circuit 7 are interpolated to obtain 8
Generate reference image data of × 16 macroblock units.

The image for the Y signal is the second reference image.
When the image is read from the reference image memory 12, the image corresponding to the read Y signal is sent to the second Y interpolation circuit 17 via the switch 16. The second Y interpolation circuit 17 reads the Y image read from the second reference image memory 12.
The vertical interpolation is performed on the reference image data of 8 × 6 macroblock units for the signal, that is, the horizontal lines thinned out by the Y thinning circuit 7 are interpolated to obtain 8
Generate reference image data of × 16 macroblock units.

The image corresponding to the C signal is the first as the reference image.
When the image is read from the reference image memory 11, the image corresponding to the read C signal is sent to the first C interpolation circuit 15 via the switch 13. The first C interpolation circuit 15 reads the C read from the first reference image memory 11.
By performing vertical interpolation on the reference image data of 4 × 3 macroblock units for the signal, that is, by interpolating the horizontal lines thinned out by the C thinning circuit 8, 4
Reference image data is generated in units of × 8 macro blocks.

The image corresponding to the C signal is the second image as the reference image.
When the image is read from the reference image memory 12, the image corresponding to the read C signal is sent to the second C interpolation circuit 18 via the switch 16. The second C interpolation circuit 18 reads the C read from the second reference image memory 12.
By performing vertical interpolation on the reference image data of 4 × 3 macroblock units for the signal, that is, by interpolating the horizontal lines thinned out by the C thinning circuit 8, 4
Reference image data is generated in units of × 8 macro blocks. Switches 13 and 16 are controlled by CPU 30.

The details of the interpolation processing performed by the Y interpolation circuits 14 and 17 and the details of the interpolation processing performed by the C interpolation circuits 15 and 18 will be described later.

The averaging unit 19 includes the first Y interpolation circuit 14.
And the image data obtained from the second Y interpolation circuit 17 or the image data obtained from the first C interpolation circuit 15 and the second C interpolation circuit 18 are averaged to obtain an interpolation result. Generating reference image data in macroblock units used for inter-frame prediction coding.

The switch 20 is controlled by the CPU 30 as follows. If the data output from the inverse DCT circuit 4 is reproduced image data for intra-frame predictive coding, the common terminal of the switch 20 is switched to the ground terminal.

When the data output from the inverse DCT circuit 4 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 20 1
A terminal to which reference image data from the Y interpolation circuit 14 or the first C interpolation circuit 15 is sent, or a reference from the second Y interpolation circuit 15 or the second C interpolation circuit 18 Switching is performed to select one of the terminals to which image data is sent.

If the data output from the inverse DCT circuit 4 is prediction error data for the interpolative inter-frame prediction code, the common terminal of the switch 20 selects the terminal to which the output of the averaging unit 19 is sent. Is switched to.

When a reference image is read from the reference image memories 11 and 12, the vector value conversion circuit 2
The cutout position is controlled based on the motion vector from Step 2.

The switch 9 is used for reproducing picture data for a B picture sent from the Y thinning circuit 7 or the C thinning circuit 8 to the switch 9 and for an I picture or a P picture stored in the reference picture memory 11. The CPU 30 controls the reproduced image data and the reproduced image data for the I picture or P picture stored in the reference image memory 12 so as to be 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 23 so as to correspond to the number of horizontal and vertical scanning lines of the monitor device, and then sent to the monitor device.

FIG. 3 shows an 8 × 6 macro obtained by thinning the first reproduced image data corresponding to the Y signal in the vertical direction at a thinning rate of 3/8 by the Y thinning circuit 7 for each 8 × 16 macroblock unit. A method for generating second reproduced image data in block units and a method for generating image data in 8 × 16 macroblock units by interpolating the second reproduced image data by the Y interpolation circuit 14 (17) are shown. ing.

FIG. 3A shows the first reproduced image data corresponding to the Y signal. MB _j−1 , MB _j , MB _{j + 1}
Indicates a macroblock. FIG. 3B shows the second reproduced image data after the first reproduced image data for the Y signal has been subjected to the thinning-out process at a thinning rate of 3/8 in the vertical direction. FIG. 3C shows image data after interpolation processing has been performed on the second reproduced image data for the Y signal. In FIG. 3, the horizontal lines in the odd fields are represented by solid lines, and the horizontal lines in the even fields are represented by broken lines.

[0066] will be described thinning out the first reproduction image data in the macro block MB _j to 3/8 in the vertical direction. 16 horizontal lines in the macroblock MB _j A1
A16 are converted into six horizontal lines B1 to B6. Each horizontal line in the macro block MB _j A1~A1
A1 (i) to A1 for each pixel position i on
6 (i), each of the six horizontal lines B1
If each pixel value on B6 is B1 (i) to B6 (i),
Each of the pixel values B1 (i) to B6 (i) on each of the six horizontal lines B1 to B6 after the thinning is represented by the following Expression 4.

[0067]

(Equation 4)

Next, the interpolation process for the second reproduced image data will be described. Constituting the data after interpolation processing corresponding to the macro block MB _j 16 horizontal lines C
Pixel values C1 (i) to C16 (i) of 1 to C16 are represented by the following Expression 5.

[0069]

(Equation 5)

FIG. 4 shows that the first reproduced image data corresponding to the C signal is decimated in the vertical direction by the decimating circuit 3 for C by the decimating circuit 8 for each 4 × 8 macroblock unit.
A method of generating the second reproduced image data in units of × 3 macroblocks, and generating the image data in units of 4 × 8 macroblocks by interpolating the second reproduced image data by the C interpolation circuit 15 (18) Shows how to do it.

FIG. 4A shows the first reproduced image data corresponding to the C signal. MB _j shows a macro block. FIG. 4 (b), the second reproduced image data after thinning-out processing when an odd-numbered macroblock macroblock MB _j shown in FIGS. 4 (a) from the top of one screen containing it Is shown.

[0072] FIG. 4 (c), FIGS. 4 (a) to the indicated macroblock MB _j second after thinning processing when an even-numbered macroblock from the top of one screen containing it This shows playback image data. FIG.
FIG. 9B shows image data after the interpolation processing has been performed on the second reproduced image data shown in FIG.

[0073] macro-block MB _j shown in FIG. 4 (a) for the thinning-out process will be described in the case where the odd-numbered macroblock from the top of one screen containing it. Represents a pixel value for each pixel i on the horizontal line A1~A8 in the macroblock MB _j with A1 (i) ~A8 (i) , each pixel value of the three horizontal lines B1~B3 after the thinning B
1 (i) to B3 (i), each pixel value B1 (i) to B3 on each of the three horizontal lines B1 to B6 after thinning out
(I) is represented by the following Equation 6.

[0074]

(Equation 6)

[0075] macro-block MB _j shown in FIG. 4 (a) for the thinning-out process will be described in the case where the even-numbered macroblocks from the top of one screen containing it. Each pixel value C1 (i) of the three horizontal lines C1 to C3 after thinning
ＣC3 (i) is represented by the following Expression 7.

[0076]

(Equation 7)

The pixel values D1 (i) to D8 (i) of the eight horizontal lines D1 to D8 constituting the data after the interpolation processing for the second reproduced image data shown in FIG.
Is represented by the following Expression 8.

[0078]

(Equation 8)

The concept of the interpolation processing for the second reproduced image data shown in FIG. 4C is the same as that of the interpolation processing for the second reproduced image data shown in FIG. Therefore, the description is omitted.

In the above embodiment, the case where the thinning rate of the thinning circuits 7 and 8 (vertical thinning rate) is 3/8 has been described. However, when the thinning rate is 1/8, 5/8, and 7/8. The present invention can also be applied to the present invention. The thinning rate is 5 /
The vertical thinning-out and interpolation processing in the case of 8 will be described.

FIG. 5 shows an 8 × 10 macro by thinning the first reproduced image data corresponding to the Y signal in the vertical direction by the Y thinning circuit 7 in units of 8 × 16 macroblocks at a thinning rate of 5/8. A method for generating second reproduced image data in block units and a method for generating image data in 8 × 16 macroblock units by interpolating the second reproduced image data by the Y interpolation circuit 14 (17) are shown. ing.

FIG. 5A shows first reproduced image data corresponding to the Y signal. FIG. 5B shows a thinning rate of 5 for the first reproduced image data for the Y signal in the vertical direction.
/ 8 shows the second reproduced image data after the thinning processing is performed. FIG. 5C shows image data after interpolation processing has been performed on the second reproduced image data for the Y signal.

[0083] will be described thinning out the first reproduction image data in the macro block MB _j in the vertical direction 5/8. 16 horizontal lines in the macroblock MB _j A1
A16 are converted into ten horizontal lines B1 to B10. The pixel values B1 (i) to B6 (i) on the ten horizontal lines B1 to B10 after the thinning are represented by the following equation (9).

[0084]

(Equation 9)

Next, the interpolation process for the second reproduced image data will be described. Constituting the data after interpolation processing corresponding to the macro block MB _j 16 horizontal lines C
The pixel values C1 (i) to C16 (i) of 1 to C16 are represented by the following Expression 10.

[0086]

(Equation 10)

FIG. 6 shows a case where the first reproduced image data corresponding to the C signal is decimated in the vertical direction by the C decimating circuit 8 in units of 4 × 8 macroblocks at a decimating ratio of 5/8 to obtain 4 data.
A method for generating the second reproduced image data in units of × 5 macroblocks and generating the image data in units of 4 × 8 macroblocks by interpolating the second reproduced image data by the C interpolation circuit 15 (18) Shows how to do it.

FIG. 6A shows the first reproduced image data corresponding to the C signal. 6 (b) is second reproduction image data after thinning-out processing when a macro block MB _j shown in FIGS. 6 (a) is an odd-numbered macroblock from the top of one screen containing it Is shown.

FIG. 6C shows a second example after the thinning-out process when the macro block MBj shown in FIG. 6A is an even-numbered macro block from the top of one screen including the macro block MB _j . This shows playback image data. FIG. 6D shows FIG.
FIG. 9B shows image data after the interpolation processing has been performed on the second reproduced image data shown in FIG.

[0090] macro-block MB _j shown in FIG. 6 (a) for the thinning-out process will be described in the case where the odd-numbered macroblock from the top of one screen containing it. Each pixel value B1 on the five horizontal lines B1 to B5 after thinning
(I) to B5 (i) are represented by the following Expression 11.

[0091]

[Equation 11]

[0092] macro-block MB _j shown in FIG. 6 (a) for the thinning-out process will be described in the case where the even-numbered macroblocks from the top of one screen containing it. Each pixel value C1 (i) of the five horizontal lines C1 to C5 after thinning
ＣC5 (i) is represented by the following Equation 12.

[0093]

(Equation 12)

The pixel values D1 (i) to D8 (i) of the eight horizontal lines D1 to D8 constituting the data after the interpolation processing for the second reproduced image data shown in FIG.
Is represented by the following Expression 13.

[0095]

(Equation 13)

The concept of the interpolation processing for the second reproduced image data shown in FIG. 6C is the same as that of the interpolation processing for the second reproduced image data shown in FIG. 6B. Therefore, the description is omitted.

In the above embodiment, the first reproduced image is generated based on the image obtained by performing the inverse DCT after removing a part of the DCT coefficient.
After the replacement, the first reproduced image may be generated based on the image obtained by performing the inverse DCT.

[0098]

According to the present invention, a first reproduced image is generated based on an image obtained by performing inverse DCT in units of 8 × 8 blocks using only a part of DCT coefficients, By performing at least the vertical thinning out of the horizontal thinning and the vertical thinning for the first reproduced image,
In a moving picture decoding method for generating a second reproduced picture having a lower resolution than an original picture, a vertical thinning rate is m /
In step 8, when m is an odd number, the quality of the reproduced image can be improved.

[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 DCT coefficients after a high-frequency portion of a horizontal spatial frequency has been removed by a horizontal high-frequency coefficient removal circuit, and data after being inversely transformed by an inverse DCT circuit;

FIG. 3 is a diagram illustrating a method of generating second reproduced image data in units of 8 × 6 macroblocks by thinning out first reproduced image data for a Y signal in a vertical direction at a decimation rate of 3/8 and a second method.
FIG. 9 is a schematic diagram for explaining a method of generating image data in units of 8 × 16 macroblocks by interpolating the reproduced image data of FIG.

FIG. 4 is a diagram illustrating a method of generating second reproduced image data in units of 4 × 3 macroblocks by thinning out first reproduced image data corresponding to a C signal at a thinning rate of 3/8 in the vertical direction, and
FIG. 9 is a schematic diagram for explaining a method of generating image data in units of 4 × 8 macroblocks by interpolating the reproduced image data of FIG.

FIG. 5 shows a method of generating second reproduced image data in units of 8 × 10 macroblocks by thinning out first reproduced image data with respect to a Y signal at a thinning rate of 5/8 in the vertical direction, and second reproduced image data FIG. 9 is a schematic diagram for explaining a method of generating image data in units of 8 × 16 macroblocks by interpolating.

FIG. 6 shows a method of generating second reproduced image data in units of 4 × 5 macroblocks by thinning the first reproduced image data for the C signal in the vertical direction at a thinning rate of 5/8, and
FIG. 9 is a schematic diagram for explaining a method of generating image data in units of 4 × 8 macroblocks by interpolating the reproduced image data of FIG.

FIG. 7 is a block diagram showing a configuration of a conventional MPEG decoder.

FIG. 8 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 3 horizontal high frequency coefficient removal circuit 4 inverse DCT circuit 5 adder 7 thinning circuit for Y 8 thinning circuit for C 11 memory for first reference image 12 memory for second reference image 14 1st Y interpolation circuit 15 1st C interpolation circuit 17 2nd Y interpolation circuit 18 2nd C interpolation circuit 19 averaging unit 21 variable length decoder 22 vector value conversion circuit 6, 9, 10, 13, 16, 20 switch 23 format conversion circuit 30 CPU

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

Claims (3)

[Claims] 1. A moving picture decoding method for decoding a signal that has been compression-encoded by the MPEG method, comprising the steps of: performing an inverse DCT using only a part of DCT coefficients; A first reproduced image is generated, and at least vertical thinning out of horizontal thinning and vertical thinning is performed on the first reproduced image, and a second reproduced image having a lower resolution than the original image is obtained. In the generated moving picture decoding method, when the original picture is an interlaced picture, the vertical thinning rate is m / 8, and m is an odd number, the luminance signal is obtained by performing inverse DCT. A first reproduced image in units of macroblocks having 16 pixels in the vertical direction is generated based on the obtained image, and 16 horizontal lines after the thinning out of the first reproduced image in units of macrobooks are generated. Smell in playback image Vertical thinning is performed so that the number of horizontal lines is converted into 2m horizontal lines and the number of horizontal lines in the odd field is equal to the number of horizontal lines in the even field in the second reproduced image after the thinning. A moving picture decoding method characterized by the following. 2. An inverse DCT after removing a part of DCT coefficients.
The moving picture decoding method according to claim 1, wherein the first reproduced picture is generated based on the picture obtained by performing T. 3. The moving image decoding method according to claim 1, wherein a first reproduced image is generated based on an image obtained by performing an inverse DCT after replacing a part of the DCT coefficients with 0.