JP3481118B2 - 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 image decoding method suitable for obtaining a reproduced image having a resolution lower than that of an original image by decoding a signal compression-coded by the MPEG system.

[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, 16 (horizontal pixel number) × 1
Predictive coding in the time axis direction (frame predictive coding in MPEG1, frame predictive coding or field predictive coding in MPEG2) is performed for each macroblock unit having a size of 6 (the number of pixels in the vertical direction). 3 of I picture, P picture, and B picture corresponding to the predictive coding method
There are different image types. 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 performing inter-frame prediction. All macroblock types in the I picture are in the frame. is only intraframe sign-reduction to encode the information.

(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 which can be formed by bidirectional prediction, and generally includes the following macroblock types. a. Frame marks Goka b to encode only intraframe information. 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 macroblock type macro blocks other than sign-of frame, inter-frame corresponding to the macro block type prediction is performed, the prediction error data is generated.

[0009] Macro image data of the block each unit (if the macroblock type is sign-of frame) or prediction error data (if the macroblock type is inter-frame prediction coding) is an 8 × 8 The image data of each sub-block is divided into four sub-blocks of a size, and a two-dimensional discrete cosine transform (D
CT: Discrete Cosine Transform) is performed based on Equation 5. That is, as shown in FIG. 10, based on each data f (i, j) in the block of 8 × 8 size,
Each DCT (orthogonal transform) coefficient F (u, v) in the uv space (u: horizontal frequency, v: vertical frequency) is obtained.

[0010]

[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 × 8 block, the lower left 8 × 8 block, and the lower right 8 × 8 block are divided. 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. 9 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. 10, 8 × 8 subblock-unit data f (i, j) is obtained based on the 8 × 8 DCT coefficient F (u, v). Also, data f in units of four sub-blocks
Based on (i, j), reproduced image data or prediction error data in one macroblock unit is generated.

[0019]

[Equation 2]

In the prediction error data in macroblock units generated by the inverse DCT circuit 103, reference image data according 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, if the data output from the inverse DCT circuit 103 is the playback image data for the sign-frame, 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 data output from the inverse DCT circuit 103 is the playback image data for the frame marks items, 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.

[0028]

By the way, when a reproduced image having a resolution lower than that of the original image is obtained, only a part of the DCT coefficients is used to perform the inverse DCT. No. 1 reproduction image is generated, and at least vertical thinning is performed on the first reproduction image among horizontal thinning and vertical thinning to generate a second reproduction image having a lower resolution than the original image. It is possible to do it.

In such a case, the first reproduced image includes the horizontal lines of the odd fields and the horizontal lines of the even fields, so that the second reproduced images obtained after thinning out also have image information with a time difference. In order to leave them together, it is preferable to perform vertical thinning so that the horizontal lines of the odd fields and the horizontal lines of the even fields are evenly included. However, if such vertical thinning is performed, the intervals of the spatial positions of the horizontal lines of the obtained second image become uneven.

The present invention is a moving image reproducing method in which vertical thinning is performed so as to generate a reproduced image in which the intervals of the spatial positions of each horizontal line are not uniform after thinning. An object of the present invention is to provide a moving image reproduction method in which, at the time of format conversion for obtaining an image, conversion of the number of horizontal lines and spatial position correction for making the spatial positions of each horizontal line substantially uniform are performed simultaneously. And

According to the present invention, the spatial position of each horizontal line is used in the moving image reproducing method in which the thinning-out in the vertical direction is performed so as to generate a reproduced image in which the spatial positions of the horizontal lines become non-uniform after thinning. It is an object of the present invention to provide a moving image reproduction method that facilitates the generation of a reproduced image in which the intervals are substantially uniform.

[0032]

A first moving picture coding method according to the present invention is a moving picture decoding method for decoding a signal compressed and coded by the MPEG system, and is a DC
A first step of generating a first reproduced image based on an image obtained by performing inverse DCT using only a part of the T coefficient, horizontal thinning and vertical direction with respect to the first reproduced image. performing at least vertical decimation of decimation, the second step of generating a lower second reproduced image resolution with respect to the original image, and format conversion combined the second reproduced image to a predetermined output format a third step of generating a third reproduced image, in the second step,
As the number of horizontal lines of the horizontal line number and an even field of an odd field of the second reproduced image obtained after thinning-out and is substantially equal, to the first reproduction picture,
Perform at least vertical decimation of the horizontal decimation and a vertical decimation, wherein in the third step, so that the distance of the spatial position of each horizontal line of said third reproduced image obtained after the format conversion is equal, the second
There rows format conversion on the reproduced image, the second
The thinning rate in the vertical thinning in step is 1/2
If the horizontal line of the first playback image is
Vertical thinning such as thinning out every two units
It is characterized by being performed .

[0033]

A second moving picture coding method according to the present invention is a moving picture decoding method for decoding a signal compressed and coded by the MPEG method, and uses only a part of DCT coefficients. A first step of generating a first reproduced image based on the image obtained by performing the inverse DCT, at least vertical thinning out of horizontal thinning and vertical thinning is performed on the first reproduced image, the second step of generating a lower second reproduced image resolution with respect to the original image, a third step of generating a third reproduced image by performing a spatial positional correction with respect to the second playback image, and the
Format the third playback image according to the specified output format.
A fourth step of generating a fourth reproduced image by preparative conversion, in the second step, and the number of horizontal lines of the horizontal line number and an even field of an odd field of the second reproduced image obtained after thinning Before to be approximately equal
At least vertical thinning out of horizontal thinning and vertical thinning is performed on the first reproduced image,
In the third step, the third step obtained after the spatial position correction is performed.
So that the distance of the spatial position of each horizontal line of the reproduced image is substantially uniform, have rows spatial position correction on the second playback image, thinning of the vertical decimation performed in the second step
When the ratio is 1/2, the water of the first reproduced image is
For example, thinning out two flat lines every two units
It is characterized in that vertical thinning is performed .

[0035]

[0036]

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

[1] Description of First Embodiment

The first embodiment of the present invention 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 20. The variable length code of the motion vector is sent to the variable length decoder 10 to be decoded. The motion vector obtained by the variable length decoder 10 is sent to the vector value conversion circuit 11 and converted so that the horizontal and vertical magnitudes of the motion vector are each halved.

The motion vector converted by the vector value conversion circuit 11 so that the magnitudes in the horizontal direction and the vertical direction are halved in the first reference image memory 7 and the second reference image memory 8, respectively. It is sent as a control signal for controlling the cutout position of the reference image.

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. As shown in FIG. 2A, the horizontal high frequency coefficient removing circuit (coefficient reducing circuit) 3 sets the DCT coefficient sequence generated by the inverse quantizer 2 to 8 (horizontal pixel number) × 8 (vertical pixel number). Number) of 8 × 8 DCT coefficients F (u, v) (where u =
0, 1, ... 7, v = 0, 1 ,. Number of DCT coefficients F of frequency direction u) × 8 (vertical frequency direction v)
(U, v) (where u = 0, 1, ... 3, v = 0, 1,
… Convert to 7).

The inverse DCT circuit 4 subjects the 4 × 8 number of DCT coefficients generated by the horizontal high frequency coefficient removing circuit 3 to the inverse DCT of 4 × 8 as shown in Formula 3, and the result shown in FIG. ) The original sub-block unit data as shown in
Data f (i, j) composed of 4 (horizontal pixel number) × 8 (vertical pixel number) data compressed to 2 (where i = 0, 1, ... 3, j = 0,1, ... 7) is generated.

[0044]

[Equation 3]

Further, one macroblock of 8 × 16 compressed in half in the horizontal direction based on the image data corresponding to the unit of four sub-blocks constituting one macroblock thus obtained. The unit reproduction image data or prediction error data is generated. Therefore, the inverse DC
The amount of data in macroblock units obtained by the T circuit 4 is half the amount of image data in macroblock units of the original image.

In the prediction error data generated by the inverse DCT circuit 4 in units of 8 × 16 macroblocks compressed in the horizontal direction by 1/2, reference image data (horizontal direction is Reference image data in units of 8 × 16 macroblocks compressed to ½) are added by the adder 5 to generate reproduced image data. The reference image data is added to the adder 5 via the switch 13.
Sent to. However, if the image data output from the inverse DCT circuit 4 is the reproduction image data to the sign-frame, the reference image data is not added.

The first reproduction image data in units of 8 × 16 macroblocks, which is obtained by the inverse DCT circuit 4 or the adder 5 and is halved in the horizontal direction, is sent to the vertical thinning circuit 21. The vertical thinning circuit 21 receives the 8
The first reproduction image data in the unit of 16 macroblocks of x16 is thinned out in half in the vertical direction to be converted into the second reproduction image data in the unit of 8x8 macroblocks.

Vertical thinning-out by the vertical thinning-out circuit 21 is performed by thinning out every two horizontal lines of the first reproduced image data by two units, as shown in FIG. In the first reproduced image data in 8 × 16 macroblock units obtained by the inverse DCT circuit 4 or the adder 5, as shown in FIG. 3A, horizontal lines of odd fields (shown by solid lines) and even fields are shown. Alternate horizontal lines (indicated by dashed lines) in the vertical direction. Therefore,
In order to evenly include the horizontal lines of the odd fields and the horizontal lines of the even fields in the image after thinning, as shown in FIG. 3B, two horizontal lines of the first reproduction image data are included. Every two units are thinned out by two units.

As a result, the first reproduced image data in units of 8 × 16 macroblocks, which is compressed in the horizontal direction by 1/2, is 8 × 8 in which both the horizontal and vertical directions are compressed by 1/2. It is converted into second reproduced image data in macroblock units. Therefore, the amount of image data in macroblock units obtained by the vertical thinning circuit 21 is ¼ of the amount of image data in macroblock units of the original image.

When the reproduced image data in macro block units obtained by the vertical thinning circuit 21 is the reproduced image data for the B picture, the reproduced image data is sent to the switch 14.

The reproduced image data in macro block units obtained by the vertical thinning circuit 21 is I picture or P
In the case of reproduction image data for a picture, the reproduction image data is stored in the first reference image memory 7 or the second reference image memory 8 via the switch 12.
First reference image memory 7 or second reference image memory 8
The amount of image data stored in is 1/4 of the conventional amount. The switch 12 is controlled by the CPU 20.

The first vertical interpolation circuit 22 performs vertical interpolation on the reference image data in 8 × 8 macroblock units read from the first reference image memory 7,
That is, the horizontal lines thinned out by the vertical thinning circuit 21 are interpolated to generate reference image data in 8 × 16 macroblock units.

The second vertical interpolation circuit 23 performs vertical interpolation on the reference image data in 8 × 8 macroblock units read from the second reference image memory 8 and
That is, the horizontal lines thinned out by the vertical thinning circuit 21 are interpolated to generate reference image data in 8 × 16 macroblock units.

The averaging unit 9 averages the image data read from the first vertical interpolation circuit 22 and the second vertical interpolation circuit 23, and is used for interpolation interframe predictive coding 8 ×.
Reference image data of 16 macroblock units is generated.

The switch 13 is controlled by the CPU 20 as follows. When data output from the inverse DCT circuit 4 is the reproduction image data to the sign-of-frame, the common terminal of the switch 13 is switched to the ground terminal.

When the data output from the inverse DCT circuit 4 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 13 is 1
It is switched to select either the terminal to which the reference image data from the vertical interpolation circuit 22 is sent or the terminal to which the reference image data from the second vertical interpolation circuit 23 is sent.

When 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 13 selects the terminal to which the output of the averaging unit 9 is sent. Is switched to.

When the reference image is read from the reference image memories 7 and 8, the cutout position is controlled based on the motion vector from the vector value conversion circuit 11. The size of the motion vector in the horizontal and vertical directions is converted to ½ by the vector value conversion circuit 11 because the image in macro block units sent from the vertical thinning circuit 21 to the reference image memories 7 and 8 is used. This is because the data is compressed in half in the horizontal and vertical directions.

The switch 14 is the second reproduction image data for the B picture sent from the vertical thinning circuit 21 to the switch 14, and the second reproduction image for the I picture or P picture stored in the reference image memory 7. data,
The CPU 20 controls so that the second reproduced image data for the I picture or P picture stored in the reference image memory 8 is output in the same order as the original image. The second reproduced image data output from the switch 14 is format-converted by the format conversion circuit 15 so as to correspond to the number of horizontal and vertical scanning lines of the monitor device, whereby third reproduced image data is obtained. Then, the obtained third reproduced image data is sent to the monitor device.

The format conversion circuit 15 performs format conversion on the second reproduced image data so that the spatial positions of the horizontal lines of the third reproduced image data obtained after the format conversion are even. That is, the format conversion circuit 15 simultaneously performs format conversion and spatial position correction.

For example, the case where the number of horizontal lines of the second reproduced image data is 540 and the number of horizontal lines of the third reproduced image data obtained after the format conversion is 480 will be described as an example.

FIG. 4 shows the second reproduced image data having 540 horizontal lines and the third reproduced image data having 480 horizontal lines.
2 shows a method of converting the format into the reproduced image data of. In FIG. 4, 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.

FIG. 4A shows the second reproduced image data. The odd lines of the second reproduced image are represented by AO _n (where n = 1, 2, ...) And the even lines of the second reproduced image are represented by AE _m (where m = 1, 2, ...). It is represented by.

FIG. 4B shows the third reproduced image data after the format conversion of the second reproduced image data. The odd lines of the third reproduced image are BO
_n (where n = 1, 2, ...), and the even lines of the third reproduced image are BE _m (where m = 1, 2,
...).

When converting 540 lines to 480 lines, the number of lines becomes 9/10. Therefore, as shown in FIG. 4, the adjacent odd line interval and the adjacent even line interval of the second reproduced image are 8d. If the interval between adjacent odd lines and even lines is 2d, the interval between adjacent odd lines and adjacent even lines of the third reproduced image is 9d, and the interval between adjacent odd lines and even lines is 4d or It becomes 5d.

The pixel value on each odd line BO _n of the third reproduced image is obtained by interpolating the pixel value on the odd line AO _n of the second reproduced image. Similarly, the pixel value on each even line BE _m of the third reproduced image is obtained by interpolating the pixel value on the even line AE _m of the second reproduced image.

Each pixel value on the target odd line of the third reproduced image is ± α · d in the vertical direction from the target odd line (where α is a value of 0 to 7 as shown in Table 1). Take)
Pixel values at corresponding positions on one or two odd lines of the second reproduced image at distant positions, and a coefficient value Z according to α
It is calculated based on (α).

Each pixel value on the even-numbered line of interest of the third reproduced image is located at a position ± αd (α takes a value shown in Table 1) in the vertical direction from the even-numbered line of interest. It is obtained based on the corresponding pixel value on one or two even lines of the second reproduced image and the coefficient value Z (α) corresponding to α.

Table 1 shows the relationship between α and Z (α).

[0070]

[Table 1]

That is, the coefficient value for the odd line of the second reproduced image having the vertical distance of ± α · d with respect to the odd line of interest in the third reproduced image is Z (α).
The odd-numbered lines of the second reproduced image whose vertical distance is ± α · d with respect to the odd-numbered line of interest in the third reproduced image are one or two.

The case where there is one odd line in the second reproduced image having a vertical distance of ± α · d with respect to the odd line of interest in the third reproduced image is that the odd line of interest is, for example, B1. As in the case, there is an odd line of the second reproduced image having a vertical distance of 0 (α = 0) with respect to the odd line of interest. In this case, each pixel value on the target odd line is a pixel at a corresponding position on the odd line of the second reproduced image whose vertical distance is 0 (α = 0) with respect to the target odd line. It will be the same as the value.

The case where there are two odd lines in the second reproduced image whose vertical distance is ± α · d with respect to the odd line of interest in the third reproduced image is that the odd line of interest is B3, for example. As in the case, one odd line (hereinafter referred to as the first odd line) of the second reproduced image whose vertical distance is in the range of 1d to 7d with respect to the odd line of interest and the odd line of interest. In contrast, the vertical distance is -7
This is the case where there is one odd line (hereinafter referred to as the second odd line) of the second reproduced image in the range of d to -1d.

In this case, each pixel value on the target odd line has a vertical distance of 1d with respect to the target odd line.
The value obtained by multiplying the pixel value at the corresponding position on one odd line of the second reproduced image in the range of ˜7d by the coefficient value Z (α) and the vertical distance with respect to the odd line of interest are − 7d
The sum is the value obtained by multiplying the pixel value at the corresponding position on one odd line of the second reproduced image in the range of to −1d by the coefficient value Z (α). Each pixel value on the target even-numbered line in the third reproduced image is similarly obtained.

FIG. 5 shows the second reproduced image data having 540 horizontal lines and the third reproduced image data having 432 horizontal lines.
2 shows a method of converting the format into the reproduced image data of. In FIG. 5, 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.

FIG. 5A shows the second reproduced image data. The odd lines of the second reproduced image are represented by AO _n (where n = 1, 2, ...) And the even lines of the second reproduced image are represented by AE _m (where m = 1, 2, ...). It is represented by.

FIG. 5B shows the third reproduced image data after the format conversion of the second reproduced image data. The odd lines of the third reproduced image are BO
_n (where n = 1, 2, ...), and the even lines of the third reproduced image are BE _m (where m = 1, 2,
...).

When 540 lines are converted to 432 lines, the number of lines becomes 8/10. Therefore, as shown in FIG. 5, the adjacent odd line interval and the adjacent even line interval of the second reproduced image are set to 8d. Assuming that the interval between the adjacent odd line and the even line is 2d, the interval between the adjacent odd line and the adjacent even line of the third reproduced image is 10d, and the interval between the adjacent odd line and the even line is 5d. Become.

As described above, although the spatial position of each horizontal line of the third reproduced image is different from that of FIG. 4, the interpolation method for obtaining each pixel value on each horizontal line of the third reproduced image will be described with reference to FIG. This is the same as the interpolation method described above.

That is, each pixel value on the target odd line of the third reproduced image is ± α · in the vertical direction from the target odd line.
d (where α is 0 to 7 as shown in Table 1 above)
The value is calculated based on the pixel value of the corresponding position on one or two odd lines of the second reproduced image at the distant position and the coefficient value Z (α) according to α.

Further, each pixel value on the noticed even line of the third reproduced image is ± α · d in the vertical direction from the noticed even line.
(However, α takes the values shown in Table 1 above.) Corresponding pixel values on one or two even lines of the second reproduced image at distant positions, and a coefficient value Z according to α It is calculated based on (α).

[2] Description of Second Embodiment

The second embodiment of the present invention will be described below with reference to FIGS.

FIG. 6 shows the structure of the MPEG decoder. 6, the same components as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In this MPEG decoder, the MPEG of FIG.
It differs from the decoder in that the spatial position correction circuit 31 is provided before the format conversion circuit 32. Further, the format conversion operation by the format conversion circuit 32 is different due to the provision of the spatial position correction circuit 31.

The spatial position correction circuit 31 performs vertical spatial position correction as shown in FIG. 7 or 8 on the second reproduced image sent through the switch 14,
A third reproduced image in which the spatial position intervals of the horizontal lines are even is generated.

FIG. 7 shows the case where only the horizontal line for one of the odd field and the even field is spatially corrected, and FIG. 8 shows the case where the horizontal line for both fields is spatially corrected.
FIG. 7A and FIG. 8A show the second reproduced image data. FIG. 7B and FIG. 8B show the third reproduction image data after the spatial position correction of the second reproduction image data. 7 and 8, 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.

7 and 8, the odd lines of the second reproduced image are represented by AO _n (where n = 1, 2, ...) And the even lines of the second reproduced image are represented by AE _m (where _m is represented by m).
= 1, 2, ...), the odd lines of the third reproduced image are represented by BO _n (where n = 1, 2, ...), and the even lines of the third reproduced image are represented by BE _m (where _m is represented by m). = 1, 2, ...)
Let be represented by.

The odd line AO of the second reproduced image_n
The pixel value corresponding to the upper position i is AO _n(I) and the second
Line AE of the reproduced image of_mImage corresponding to position i above
AE as the prime value_m(I), an odd line of the third reproduced image
BO_nThe pixel value corresponding to the position i above is BO_n(I) and
And the even line BE of the third reproduced image_mPair with position i above
The corresponding pixel value is BE_m(I).

In FIG. 7, each pixel value BO _k (i) corresponding to the position i on the target odd line BO _k of the third reproduced image with n = k and the third reproduced image with m = k. Each pixel value BE _k (i) on the target even line BE _k is expressed by the following mathematical formula 4.

[0091]

[Equation 4]

In FIG. 8, each pixel value BO _k (i) corresponding to the position i on the target odd line BO _k of the third reproduced image of n = k and the third reproduced image of m = k. attention even lines bE each pixel on _k values bE _k (i) is expressed by the following equation 5.

[0093]

[Equation 5]

The format conversion circuit 32 makes the third reproduced image obtained by the spatial position correction circuit 31 in which the spatial position intervals of each horizontal line are equal to correspond to the number of horizontal and vertical scanning lines of the monitor device. And the fourth reproduction image is generated. Also in this case, the format conversion is performed so that the spatial position intervals of the respective horizontal lines of the fourth reproduced image obtained after the formatting become equal, but the horizontal conversion of each horizontal line of the third reproduced image which is the format conversion target is performed. Since the spatial position intervals are uniform, the format conversion processing by the format conversion circuit 32 becomes simple.

In the above first or second 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.
The first reproduced image may be generated based on the image obtained by performing the inverse DCT after replacing a part of the T coefficient with 0.

[0096]

According to the present invention, in the moving image reproducing method in which the thinning in the vertical direction is performed so that the reproduced image in which the intervals of the spatial positions of the horizontal lines become non-uniform after the thinning is generated, the output format A method for playing back moving images was obtained, in which the number of horizontal lines was converted and the spatial positions were corrected at the same time to make the spatial positions of each horizontal line almost uniform when the format was converted to obtain a reproduced image according to To be

Further, according to the present invention, in the moving image reproducing method in which vertical thinning is performed so as to generate a reproduced image in which the spatial positions of the horizontal lines are not uniform after thinning, There is provided a moving image reproducing method in which it is easy to generate a reproduced image in which the spatial positions of lines are substantially uniform.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram showing the DCT coefficients after the high-frequency part of the horizontal spatial frequency is removed by the horizontal high-frequency coefficient removing circuit, and the data after being inversely transformed by the inverse DCT circuit.

FIG. 3 is a schematic diagram for explaining thinning processing by a vertical thinning circuit.

FIG. 4 is a schematic diagram for explaining a method of format-converting second reproduction image data having 540 horizontal lines into third reproduction image data having 480 horizontal lines.

FIG. 5 is a schematic diagram for explaining a method of format-converting second reproduction image data having 540 horizontal lines into third reproduction image data having 432 horizontal lines.

FIG. 6 is a block diagram showing a configuration of an MPEG decoder that is a second embodiment.

FIG. 7 is a schematic diagram for explaining spatial position correction performed by a spatial position correction circuit 31.

FIG. 8 is a schematic diagram for explaining another example of the spatial position correction performed by the spatial position correction circuit 31.

FIG. 9 is a block diagram showing a configuration of a conventional MPEG decoder.

FIG. 10 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 3 Horizontal high frequency coefficient removal circuit 4 Inverse DCT circuit 5 adder 7 First reference image memory 8 Second reference image memory 9 Averaging unit 10 Variable length decoder 11 Vector value conversion circuit 12, 13, 14 switch 15, 32 format conversion circuit 20 CPU 21 Vertical thinning circuit 22 First Vertical Interpolation Circuit 23 Second Vertical Interpolation Circuit 31 Spatial position correction circuit

Front page continuation (72) Inventor Akihiko Yamashita 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-8-205161 (JP, A) JP-A-9- 247673 (JP, A) JP-A-3-48587 (JP, A) JP-A-5-304657 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N ^7/ 24-7 / 68 H04N 7/00-7/088

Claims (2)

(57) [Claims] 1. A moving picture decoding method for decoding a signal compressed and coded by the MPEG method, which is based on an image obtained by performing an inverse DCT using only a part of DCT coefficients. A first step of generating a first reproduced image; at least a vertical thinning out of a horizontal thinning and a vertical thinning is performed on the first reproduced image to obtain a second low resolution image with respect to the original image. the second step of generating a reproduced image, a third step of generating a third reproduced image by format conversion combined the second reproduced image to a predetermined output format, the second step is obtained after thinning to the second, as the number of horizontal lines of the horizontal line number and an even field of an odd field of the reproduced image is substantially equal, the first reproduced image is, horizontally Mabikioyo Perform at least vertical decimation of the vertical decimation, and in the third step, obtained after format conversion
So that the distance of the spatial position of each horizontal line of said third reproduced image becomes uniform, have rows format conversion on the second playback image, the thinning rate in the vertical decimation performed in the second step 1
/ 2, the horizontal line of the first reproduced image
Vertical direction such as thinning out every 2 units by 2 units
A moving picture decoding method characterized by thinning . 2. A moving picture decoding method for decoding a signal compressed and coded by the MPEG method, which is based on an image obtained by performing an inverse DCT using only a part of DCT coefficients. A first step of generating a first reproduced image; at least a vertical thinning out of a horizontal thinning and a vertical thinning is performed on the first reproduced image to obtain a second low resolution image with respect to the original image. the second step of generating a reproduced image, the third perform spatial position correction with respect to the second reproduced image
Four combined third step of generating a reproduced image, and the third reproduced image to a predetermined output format
A fourth step <br/> generating a fourth reproduced image by mat conversion, in the second step, the horizontal of the horizontal line number and an even field of an odd field of the second reproduced image obtained after thinning so that the number of lines substantially equal, to the first playback image, perform at least vertical decimation of the horizontal decimation and a vertical decimation, and in the third step, the obtained after spatial position correction Three
So that the distance of the spatial position of each horizontal line of the reproduced image is substantially uniform, have rows spatial position correction on the second playback image, the thinning rate in the vertical decimation performed in the second step is 1
/ 2, the horizontal line of the first reproduced image
Vertical direction such as thinning out every 2 units by 2 units
A moving picture decoding method characterized by thinning .