JP2002218470A - Method for converting image encoded data rate and device for converting image encoding rate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an image encoded data rate converting method in which delay time is short and image quality deterioration is small without decoding an encoded image signal up to the level of image data. SOLUTION: This image encoded data rate converting method is realized in such a manner that a signal separating means 13 divides a signal encoded by motion compensation prediction and conversion encoding into an encoded image signal and encoded information, an image rate converting means 22 performs rate conversion processing of coefficient data of each pixel block to obtain update processing coefficient data, and an image data converting means 25 generates a skip macroblock by eliminating the image data of a pixel block when the motion vector quantity of the pixel block is not larger than a prescribed value or when the image data are not used as a reference frame image for decoding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to rate conversion of coded image data encoded at a predetermined transfer rate.
In particular, the present invention relates to a rate conversion method for image encoded data and an image encoding rate conversion apparatus capable of performing rate conversion with a simple configuration in a device that records, transmits, or displays encoded moving images.

[0002]

2. Description of the Related Art As a technology for encoding moving picture signals such as television signals with high efficiency, an MPEG-standard is used as an international standard.
2 (moving picture experts group -2) is ISO / I
EC (International Organization for Standardizati
on / International Electrotechnical Commission).

[0003] MPEG-2 divides a "frame" image constituting a moving image into 16 x 16 pixel blocks called "macroblocks".
A motion amount called a “motion vector” is obtained between a reference image and a coded image separated by a predetermined number of frames in the future or the past in time, and the coded image is encoded from the reference image based on the motion amount. A DCT (Discrete Cosine) technique, which is one of orthogonal transform techniques, is applied to an "motion compensated prediction"
Transform: Discrete cosine transform), which converts image information into a frequency information amount, and then performs compression encoding by obtaining only visually significant information. It is stipulated on the basis of elemental technologies for chemical conversion.

[0004] The transfer rate of a signal image-encoded by the technique specified in this manner is set within a fixed transfer rate at which the transmission capacity per unit time is almost constant and a fixed transfer rate. Two types of setting methods are used: a variable transfer rate at which the transfer is performed with a variable transmission capacity.

[0005] Signals encoded using the MPEG-2 standard are used in digital broadcasts, recording media such as DVDs, and communication paths such as ATM (Asynchronous Transfer Mode). The bit rate indicating the transmission capacity of the bit stream per unit time can be freely selected within a certain range according to the application.

As described above, since coded signals having different transfer rates are used depending on applications, the coded signals having different transfer rates are transmitted at a rate of, for example, 7 Mbps (M bit / bit).
Second) digital broadcast signal cannot be recorded on a digital recorder set to a recording rate of, for example, 4 Mbps.

At this time, there is a method of recording by setting the recording capacity of the recorder to a large bit rate in accordance with the signal rate of digital broadcasting. In this case, it is necessary to secure a large recording area on the recording medium of the recorder. Therefore, a problem such as a reduction in recording time occurs, which is not preferable.

Therefore, a 7 Mbps bit rate signal is
The signal is converted into a signal of a new bit rate of Mbps and then recorded on the recorder, so that a predetermined recording time is secured.

The rate conversion is performed when a bit stream broadcast at a fixed transfer rate is recorded at a variable transfer rate, or a bit stream broadcast at a variable transfer rate opposite thereto is recorded at a fixed transfer rate. There is also a need for rate conversion processing when switching between such fixed and variable bit rate setting methods.

As described above, as a method of performing a rate conversion and generating a bit stream of another transfer rate from a bit stream of a certain transfer rate, conventionally, a supplied bit stream is decoded to a pixel level by a decoder and decoded. After generating an image, the generated decoded image is supplied to an encoder to perform encoding again, so-called “re-encoding”.
Method has been used.

However, re-encoding requires both a decoder and an encoder. In addition, an image memory for temporarily storing decoded images is required for encoding, and the circuit scale is increased. There is a problem that the encoding and re-encoding processes are delayed.

As a rate conversion method for solving the problem, variable length decoding (VLD; decoding of variable l) is performed without decoding an input bit stream to a pixel level.
DCT obtained by performing the encoding and the inverse quantization
A rate conversion method for re-quantizing coefficients with a quantization scale of a different value to obtain a bit stream of a required bit rate is disclosed in Japanese Unexamined Patent Application Publication No. 7-312756, entitled "Information Conversion Circuit for Compressed Video Code Signal , Apparatus and methods ".

FIG. 14 shows a configuration of a rate conversion device in a conventional example having such a configuration. In the figure, a supplied 4 Mbps bit stream is separated into an image signal and other signal parts by a data separation circuit 81, and the image signal is converted into a V-length signal by an inverse VLC (variable length coding) circuit 82.
The LC-decoded signal is decoded, and the signal obtained by the decoding is inversely quantized by an inverse quantizer 83, and then quantized by a quantizer 85 controlled by a bit rate control circuit 84. The signal obtained by the conversion is subjected to VLC by a VLC circuit 86, the signal obtained by the VLC is combined with a signal separated by a data separation circuit 81 by a combining circuit 87, and the combined signal is temporarily stored in a buffer circuit 88. The stored and temporarily stored signal whose transfer rate has been converted to 2 Mbps is read out from the buffer circuit 88 as necessary, and supplied as an output signal from the rate converter.

In this manner, a signal whose rate has been converted by inverse quantization and requantization can be obtained.
As another rate conversion method, when the bit rate after the rate conversion is lower than that before the conversion, the variable length code corresponding to the DCT coefficient portion after the quantization of the input bit stream is adjusted to reduce the code length. A rate conversion method for shortening and obtaining a bit stream of a required bit rate is disclosed in Japanese Patent Application Laid-Open No. H11-317942, entitled "Image Encoding Apparatus".

[0015]

By the way, rate conversion is performed without decoding and re-encoding a bit stream signal up to the pixel level as in the above-mentioned conventional example.
In the method of performing the rate conversion by directly adjusting the variable length code of the DCT coefficient portion, for example, the D
When adjusting the CT coefficient, etc.
If the T coefficients are all zero, the CBP of the macroblock containing that block in the bitstream
(Coded block pattern) data had to be changed, and the CBP information was changed.

[0016] In the case of coding that is usually performed for the macroblock, when the same image is coded at a different bit rate, skipping is performed with a low-rate coded signal as compared with a high-rate coded signal. The number of macroblocks that are performed often increases.

However, in the above-described conventional example, although adjustment is possible up to the change of CBP, adjustment for increasing the number of skipped macroblocks cannot be performed.
In particular, the conversion of a coded signal to a low rate not only cannot sufficiently reduce the code amount due to the code amount of a motion vector or the like, but also performs processing such as greatly reducing the coefficient of a block in which DCT coefficients should be left. In other words, the image quality is only greatly deteriorated.

Also, in the case of rate conversion by requantization, similarly, since the number of macroblocks to be skipped when the rate after conversion is low does not increase, the code amount cannot be sufficiently suppressed. As a result, these rate conversion methods have not been effectively used, for example, coarse quantization has to be performed in blocks where DCT coefficients are to be left, and image quality is greatly deteriorated.

Accordingly, the present invention is capable of generating a bit stream obtained by encoding according to an encoding method such as MPEG-2, and a skip macroblock in the same manner as the encoding according to those encoding methods. , And CBP as a data structure, and encodes a motion vector to perform variable-length encoding of DCT coefficients after quantization using a two-dimensional VLC table. Against
Performing rate conversion of encoded image data and performing coefficient reduction processing on DCT coefficients after rate conversion in each block without performing re-encoding such that decoding is performed to the pixel level and then rate conversion is performed. And to a rate conversion processing method realized by

That is, in the rate conversion processing performed in this manner, when the processed DCT coefficient is within a predetermined range, the coefficient of the block is set to “0” and the CBP of the macroblock to which the block belongs is changed. In particular, a rate conversion processing method capable of performing a sufficient coefficient reduction processing at the time of conversion to a low rate and having a low image quality deterioration, and a configuration of a rate conversion processing apparatus equipped with the processing method are described. It is something to offer.

[0021]

The present invention comprises the following means 1) to 6) to solve the above-mentioned problems. That is,

1) A moving image signal is divided into a plurality of image data for each pixel block of a predetermined size, a motion vector amount is obtained for each of the divided pixel blocks, and a motion vector is calculated based on the obtained motion vector amount. An encoded image signal is obtained by performing orthogonal transformation of the image data of the pixel block while performing compensation prediction, quantizing the data obtained by the orthogonal transformation, and performing variable length coding on the data obtained by the quantization. , And obtains information of coding parameters related to generation of the coded image signal as coding information, generates a header signal including the obtained coding information, and generates the generated coded image signal. And the header signal to obtain first coded data compressed and coded at the first transfer rate, and the obtained first coded data is supplied to the first coded data. A method of converting the rate of encoded image data obtained by converting encoded data into second encoded data compressed and encoded at a second transfer rate, the method comprising:
A first step (13) of obtaining the coded image signal and the coded information from the coded data, and orthogonalizing the coded image signal based on the coded information obtained in the first step. The image data for each pixel block obtained by the conversion is obtained, and when the motion vector amount of the pixel block related to the obtained image data is equal to or less than a predetermined value, or when the image data related to the pixel block is When the interval of the motion prediction used as the reference frame image for decoding is equal to or less than a predetermined number of frames, update image data obtained by deleting at least one of the image data or the difference image data from the reference frame image for motion compensation prediction decoding is deleted. A second step (25) for generating and an encoded image signal updated based on the updated image data generated in the second step. Generates Goka information, a third step of obtaining a header signal including the generated coded information (2
6) and the header signal obtained in the third step,
A fourth step (2) of combining the updated image data generated in the second step to obtain the second encoded data;
9, 32), wherein the rate of the encoded image data is converted.

2) The updated image data in the second step is obtained by converting coefficient data for each pixel block obtained by orthogonally transforming an image signal related to the image data into the second image data.
Wherein the image data generated based on the update coefficient data subjected to the rate conversion processing based on the transfer rate of the image data is subjected to deletion processing. .

3) The updated coefficient data is subjected to inverse quantization using the quantization scale used to obtain the coefficient data, and the image data obtained by inverse quantization is used to obtain second encoded data. 2. The method according to item 2), wherein the image data is obtained by requantization using the updated updated quantization scale.

4) The deletion of the image data relating to the pixel block in the third step is performed by sequentially decreasing the coefficient data of the higher order obtained by orthogonally transforming the pixel block. 3. A rate conversion method for the encoded image data described in the item.

5) The deletion of the image data in the third step is performed when the image data related to the pixel block is
When the image type is not used as a reference frame image, a predetermined value for a non-reference image in which a motion vector amount of a pixel block is set to be larger than the predetermined value is set, and image data relating to the pixel block is deleted. The rate conversion method of the encoded image data according to 1), wherein the updated image data is generated.

6) The moving image signal is divided into a plurality of image data for each pixel block of a predetermined size, a motion vector amount is obtained for each of the divided pixel blocks, and a motion vector is calculated based on the obtained motion vector amount. An encoded image signal is obtained by performing orthogonal transformation of the image data of the pixel block while performing compensation prediction, quantizing the data obtained by the orthogonal transformation, and performing variable length coding on the data obtained by the quantization. , And obtains information of coding parameters related to generation of the coded image signal as coding information, generates a header signal including the obtained coding information, and generates the generated coded image signal. And the header signal to obtain first coded data compressed and coded at the first transfer rate, and the obtained first coded data is supplied to the first coded data. An encoded image data rate conversion device obtained by converting encoded data into second encoded data compressed and encoded at a second transfer rate, wherein said encoded image signal is converted from said first encoded data to said encoded image signal. And a signal separating means (13) for obtaining the coded information, and when a motion vector amount of a pixel block obtained by orthogonally transforming the coded image signal is equal to or less than a predetermined value or relating to the pixel block. When a motion prediction interval in which image data is used as a reference frame image for motion compensation prediction decoding is equal to or less than a predetermined number of frames, at least a difference image of the pixel block from the image data or the reference frame image for motion compensation prediction decoding. Image data conversion means (25, 25a) for generating updated image data in which one of the data has been deleted, and Header signal updating means (26) for generating encoded information relating to an encoded image signal updated based on the updated image data and obtaining a header signal including the generated encoded information; And signal combining means (29, 32) for combining the header signal obtained in step (1) and the updated image data generated by the image data converting means to obtain the second encoded data. Coded data rate conversion device.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a preferred embodiment of an image encoding data rate conversion method and an image encoding rate conversion apparatus according to the present invention will be described. FIG.
This is a configuration of an image encoding rate conversion device equipped with the image encoded data rate conversion method, and will be described below with reference to the drawings.

An image coding rate converter 10 shown in FIG.
Is a device that performs rate conversion by inverse quantization and requantization, and the device is a DEMUX (de-multiplexin).
g) unit 11, input code amount counter 12, header separation unit 1
3, header data storage unit 14, header combining unit 15, output code amount counter 16, re-MUX (multiplexing) unit 1
7, and an image rate conversion unit 20 that performs rate conversion by inverse quantization and requantization.

Next, the operation of the image coding rate converter 10 configured as described above will be described. First, at a predetermined data rate, MPEG-2 (moving picture experts)
The bit stream encoded according to the group-2) method includes an image signal encoded by the DEMUX unit 11, an audio signal attached to the image signal, auxiliary signals such as character information, and a method of reproducing these signals. And other signals related to the MPEG-2 system for performing control, synchronization and the like.

The other signal portions obtained separately are supplied to the re-MUX unit 17, and the separated image signals are supplied to the input code amount counter 12, where the code amount of the image signals is counted. , A part of the signal obtained by the counting is supplied to the image rate conversion unit 20, and the other part is supplied to the header separation unit 13.

In the header separation section 13, data of a layer above the slice layer such as a sequence header and a picture header is separated from the supplied image signal, and the separated signal is supplied to a header data storage section 14. The temporarily stored signal is supplied to the header combining unit 15 as needed, and the pre-conversion bit rate information recorded in some other sequence headers and the encoded image signal are It is supplied to the image rate conversion unit 20.

In the image rate conversion unit 20, the header separation unit 13 uses the pre-conversion bit rate information supplied from the input code amount counter 12 and the post-conversion bit rate information supplied from the output code amount counter 16. Perform image rate conversion of the supplied encoded image signal,
The converted image signal obtained by the conversion is supplied to the header combining unit 15 and combined with the header signal supplied from the header data storage unit 14. The combined signal is supplied to the output code amount counter 16. You.

For the signal supplied to the output code amount counter 16, the bit rate of the encoded signal is measured to obtain the above-mentioned converted bit rate information. The audio signal which is supplied to the MUX unit 17 and added to the above-mentioned image signal and other signal parts related to the MPEG-2 system are added and supplied from the image encoding rate conversion device 10 as an MPEG-2 stream output signal. Is done.

As described above, the MPEG-2 stream whose encoding rate has been converted is supplied as an output signal from the image encoding rate converter 10, and then the image rate converter, which is a main part of the converter, is supplied. About the operation of 20,
This will be described together with the encoding operation performed by the MPEG-2 encoding method.

FIG. 2 shows the configuration of an MPEG-2 encoder that encodes a moving picture signal specified by MPEG-2.

The MPEG-2 encoder 60 includes a subtractor 61, a DCT (Discrete Cosine Transform) unit 62,
Quantizer 63, code amount controller 64, variable length encoder 6
5, buffer 66, inverse quantizer 71, IDCT (Invers
e Discrete Cosine transform) unit 72, adder 73,
It comprises a frame memory 74 and a motion compensation predictor 75.

The operation of the MPEG-2 encoder 60 configured as described above will be described. First, the supplied moving image signal is supplied to one input terminal of a subtractor 61 and also to a motion compensation predictor 75, where a moving vector of the moving image signal is obtained, and based on the obtained moving vector, The motion prediction signal is supplied to one input terminal of an adder 73, and the motion prediction signal is supplied to a subtractor 61 as a subtraction input signal.

The difference signal obtained by subtracting the motion prediction signal from the supplied moving image signal from the subtracter 61 is a DCT signal.
The DCT unit 62 performs a discrete cosine transform of the supplied difference signal, and a cosine frequency component obtained by the cosine transform is supplied to a quantizer 63.

In the quantizer 63, a code amount control unit 64
Of the cosine frequency components supplied from the DCT unit 62 based on the control signal supplied from the DCT unit 62, a frequency component effective for image encoding is obtained as a quantized signal, and the obtained quantized signal is variable. The signal is supplied to the long encoder 65 and also to the inverse quantizer 71.

The quantized signal supplied to the inverse quantizer 71 is inversely quantized to obtain an approximate cosine frequency component, and the obtained approximate cosine frequency component is supplied to the IDCT unit 72. Thus, an approximate image difference signal is obtained.

The obtained approximate image difference signal is supplied to the adder 73, and the approximate image signal is decoded so as to be added to the above-mentioned motion prediction signal, and the decoded image signal is decoded. Are stored in the frame memory 74,
The image signal stored in the frame memory 74 is used to generate a motion-compensated predicted image for the frame image of the next incoming moving image signal.

The video signal is encoded while the motion-compensated predicted image is generated as described above. The quantized signal supplied to the above-mentioned variable-length encoder 65 is subjected to variable-length encoding and variable-length encoding. The signal obtained by the long encoding is temporarily stored in a buffer 66 and supplied as an encoded bit stream, and a part of the signal temporarily stored in the buffer 66 is supplied to a code amount control unit 64. The code amount control unit 64 detects the code amount of the generated bit stream, and generates a control signal for controlling the quantization roughness of the quantizer 63 based on the detected code amount information. The quantizer 63 generates an encoded signal at a predetermined bit rate.

As described above, the supplied moving picture signal is subjected to picture coding using the motion compensation prediction technique and the transform coding technique. Next, the image signal on which the image encoding is performed is formed into an encoded picture for each predetermined frame image, and motion compensation prediction is performed. In the MPEG-2 system, a prediction frame image on which motion compensation prediction is performed is performed. The configuration will be described.

FIG. 3 shows a coded picture structure for explaining the relation between picture images for which motion vectors are obtained and motion compensation is performed for motion compensation prediction performed by the coding device 60.

The structure of an encoded picture based on the motion compensated prediction shown in FIG. 1 includes an I (Intra-coded) picture (intra-frame encoding) and a P (Predictive).
-coded) picture (forward predictive coding), and B
(Bidirectionally predictive-code
d) It is composed of a combination of three types of pictures having different motion prediction methods, called pictures (bidirectional predictive coding).

The frame-by-frame image signal constituted by such a motion prediction structure is constituted by an ordinary video signal of 30 frames per second, and in the case of movie material, an image signal of 24 frames per second. Transform coding of a signal will be described.

FIG. 4 shows a method of image division for the transform coding. In the figure, the frame image has a width of 16
This indicates that image compression processing is performed by dividing the image into a horizontally long image called a slice composed of book scanning lines.

As a pixel unit for the image compression processing, a slice is divided into 16 pixels in the horizontal direction, and a pixel unit of 16 pixels × 16 scanning lines (pixels) obtained by division is called a macroblock. It is a pixel unit.

The macro block as a pixel unit is composed of four luminance signal blocks of 8 pixels × 8 pixels,
Transform coding is performed by dividing into a total of six blocks including a color difference signal block in which each of blue and red is 8 pixels × 8 pixels.

The image data thus transformed and encoded includes a slice layer composed of encoded data relating to image data composed of slices, a macroblock layer relating to data of each macroblock, and a macroblock. Are coded data composed of data of each layer such as a block layer composed of DCT coefficient data obtained by quantizing the six blocks constituting.

The data of each layer configured in this manner is
Data that is transmitted following a header such as a sequence header or a picture header is called a bit stream.

FIG. 5 shows the MPEG transmitted in such a manner.
2 shows a data structure of a bit stream in -2. In the figure, the data to be transmitted is shown to be composed of header data, slice layer data, macro block layer data, and block layer data.

FIG. 6 shows a data structure in the macro block layer. The data in the macroblock layer is
Macro block escape, macro block address increment, macro block type, motion type, DCT type, Q scale code, motion vector, and CBP (coded block pattern) are arranged in this order.

The macroblock types in these arrays indicate the prediction mode, the presence or absence of a quantized scale code, and the presence or absence of a coding coefficient for each picture type represented by I, P, and B. The updated scale code is transmitted such that the updated value is transmitted only when the quantization scale is updated in the macroblock in the slice.

Next, a macroblock type VLC (variable length) for each picture given by the I, P, B
h coding) table. FIG. 7 shows the macroblock type VL for I-pictures in those pictures.
This is a C table. When the code is “1”, the description indicates that the code is an intra code, and when the code is “01”, it indicates that the quantization scale code is arranged later. Is shown.

FIG. 8 shows a macroblock type VLC table for a P picture, which shows a state in which motion prediction coding (MC: Motion Compensation) is performed by a description for the code, and quantization. This shows the status of the scale code (Quant).

FIG. 9 is a VLC table of a macro block type for a B picture.
ward) shows the state of the prediction coded data regarding prediction from an image and prediction from a backward (Bwd: backward) image.

In this way, the macroblock type information is arranged and transmitted as a bit stream.
The CBP is arranged at the end of the macro block layer, and indicates whether or not the quantized DCT coefficient data of the subsequent block layer exists in each of the six blocks.

When the macroblock type is an intra macroblock which is intra-coded image data, at least one coefficient data exists in every block. The last CBP is made nonexistent.

When coefficients do not exist in all blocks in one macro block, the macro block is set to "Not Coded".

Further, in the case of frame structure coding, when the motion type (motion prediction type) is frame prediction, and all the motion vectors are “0” in P pictures (this is called “No MC”), When "Not Coded" is reached, the macroblock is skipped, that is, not coded,
It can be.

Similarly, the motion type (motion prediction type) is frame prediction, the prediction direction of a B picture such as forward prediction, backward prediction or bidirectional prediction, and the macroblock immediately before the slice having the same motion vector. If they are the same, the macroblock can be skipped, that is, not encoded, as “Not Coded”.

The data of the macro block layer is arranged in this manner, and the data of the block layer is arranged after the macro block layer. Next, the data structure of the block layer will be described. FIG. 10 shows a data structure in the block layer.

In the figure, a block layer has a DC (direct current) coefficient of an image obtained by performing a DCT operation on image data of an intra macroblock and AC which is a cosine frequency component.
(AC) coefficients and the E transmitted after the completion of those coefficients
They are arranged in the order of OB (end of block).

Then, the quantized DC in the block layer
The encoding of the T coefficient data is different between the intra macroblock and the other macroblocks. In the case of the intra macroblock, only the DC coefficient which is the first coefficient is
VLC (variable length coding) is performed by different methods.

That is, the coefficients other than the DC coefficients of the intra macroblock and the coefficients of the other macroblocks are rearranged in the designated order, and the number (run) of leading zero coefficients in that order and the non- Zero coefficient value (level)
Are checked and encoded by means of a two-dimensional VLC table showing the runs and levels in one set.

In the coding by the two-dimensional VLC table, a code called EOB (end of block) is added when the non-zero coefficient is lost, and the coding of the block is completed.

As described above, the moving picture signal is encoded by MPEG-2, and the arrangement according to the predetermined method for transmitting the encoded image data and the bit stream generated by arrangement are described.

Next, a method of converting the coded signal generated at a predetermined bit rate into a signal having another desired bit rate will be described.

The conversion is performed, for example, when a received signal digitally broadcast by the MPEG-2 system is recorded on a digital VTR at a bit rate smaller than that of the broadcast in order to lengthen the recording time.

If the conversion of the bit rate is performed by converting a digital signal into an analog signal and then converting it into a digital signal again, the processing time for the conversion becomes long. The delay time becomes an obstacle when simultaneous monitoring of recording signals is performed simultaneously, and when a digital signal is converted into an analog signal and then converted again into a digital signal, the image quality deteriorates due to the conversion. An object of the present invention is to realize a configuration of an image coding rate conversion apparatus that does not deteriorate image quality due to re-conversion, and will be described below with a plurality of embodiments.

FIG. 11 shows the configuration of an image coding rate converter according to the first embodiment. The image coding rate conversion device 10 is a device that performs rate conversion by inverse quantization and requantization.

Then, the image coding rate converter 1
0 indicates a DEMUX (de-multiplexing) unit 11, an input code amount counter 12, a header separation unit 13, a header data storage unit 14, a header combining unit 15, an output code amount counter 16,
A re-MUX (multiplexing) unit 17, a variable-length decoding / separation unit 21, an inverse quantization / re-quantization unit 22, a code amount control unit 23,
MV (motion vector) data determination unit 24, coefficient operation unit 25, MB (macro block) data change unit 26, MBA
(Macro block address) memory 27, two-dimensional VLC (v
ariable length coding) unit 28 and data combining unit 2
9.

Next, the operation of the image coding rate converter 10 configured as described above will be described.

First, at a predetermined data rate, MPEG-2
The bit stream encoded according to the method is a DEMU
The image signal encoded by the X section 11 and the audio signal attached to the image signal and other signal parts related to the MPEG-2 system are separated, and the other signal parts obtained by the separation are While being supplied to the re-MUX unit 17, the image signal is also supplied to the input code amount counter 12, where the code amount of the image signal is counted, and a part of the counted signal is supplied to the code amount control unit 23. The other part is supplied to the header separating unit 13.

In the header separating section 13, data of a higher layer than the slice layer such as a sequence header and a picture header is separated from the supplied image signal, and the separated signal is supplied to the header data storage section 14. The bit rate information before conversion, which is temporarily stored and recorded in the sequence header which is another part, is stored in the code amount control unit 23.
Is supplied to the variable-length decoding / separating unit 21.

The signal supplied to the variable-length decoding / separating unit 21 and separated from the header data is divided by the variable-length decoding / separating unit 21 into a DCT (discrete cosine transform) coefficient part and other parts. The DCT coefficient part is variable-length decoded, and the pre-transform quantization scale code obtained by decoding is supplied to the inverse quantization / requantization unit 22, and the other signals are supplied to the MB data change unit 26. At the same time, the motion vector data is
, And the pre-conversion quantization scale code recorded in the slice layer and the macroblock layer is supplied to the code amount control unit 23.

The code amount control section 23 is supplied with the pre-conversion bit rate information, the post-conversion target bit rate, and the pre-conversion quantization scale code, and further supplied from the input code amount counter 12 and the output code amount counter 16. Code amount of each image before and after the conversion, and the inverse quantization / requantization unit 22
The information such as the code amount before and after the rate conversion of each macro block counted by the above is supplied.

The code amount control unit 2 to which these information are supplied
In 3, an average value of the code amount for each image with respect to the quantization scale before and after the conversion of each image is calculated based on the information, and a predetermined method for the obtained code amount, for example, By controlling the code amount by the method specified in Steps 1 and 2 of MPEG-2 Test Model 5, the quantization scale after conversion is determined, and the determined quantization scale after conversion is inverse quantization / requantization. Is supplied to the conversion unit 22.

The inverse quantization / requantization unit 22 supplies the DCT coefficient portion and the pre-transform quantization scale code which have been subjected to the variable-length decoding by the variable-length decoding / separation unit 21, and the supplied pre-transform quantization scale. An actual pre-transform quantization scale is obtained based on the scale code, and the DCT coefficient part supplied is de-quantized using the obtained pre-transform quantization scale,
The quantized signal obtained by the inverse quantization is transmitted to the code amount control unit 23.
Is re-quantized based on the converted quantization scale supplied from.

The coded image signal supplied at the predetermined transfer rate in this manner is converted into a coded signal converted to a coded image signal of a desired transfer rate, and is output from the image coding rate conversion device 10. Supplied as a signal.

The conversion of the coding rate by the image coding rate converter 10 has been described above. In the example of the transform apparatus 10, for the sake of simplicity, the inverse quantization and requantization unit 22 performs both inverse quantization and requantization simultaneously. It goes without saying that the quantization unit and the requantization may be individually performed by the requantization unit.

Here, the inverse quantization and requantization operations will be further described. In the above-mentioned inverse quantization / requantization unit 22, the conversion of the coding rate is performed by changing the quantization scale, and the change of the quantization scale is performed by the quantization scale before the conversion and the quantization scale after the conversion. , And multiply each DCT coefficient before transformation by a scale ratio constant obtained by dividing the quantization scale before transformation by the quantization scale after transformation to perform inverse quantization and requantization processing. I have to.

On the other hand, when the quantization scales used before and after the conversion are the same, there is no need to perform the inverse quantization and requantization, and the DCT coefficient part before the conversion is used as it is after the conversion. It is supplied as a DCT coefficient part.

The coefficient operation section 25 cuts (deletes) a predetermined DCT coefficient from the requantized DCT coefficient based on the code amount control information supplied from the code amount control section 23.

That is, the cut of the DCT coefficient is based on a picture type such as whether the picture is an I, P, or B frame, a block type such as whether the type of image data is a luminance signal or a color difference signal, or the like. The position and the number of coefficients to be cut are specified according to the value of the target bit rate after the rate conversion and the target code amount allocated to the macroblock being cut.

In this way, when a high target bit rate after a change such that a sufficient code amount is allocated to each macroblock is given, the coefficient is not cut to prevent the image quality from being deteriorated. When the target bit rate is given as a low rate such as 2 Mbps, the target code amount assigned to each macroblock is often insufficient, and the number of coefficients to be cut is increased to increase the The data determination unit 24 generates more skipped macroblocks.

The data of the macroblock is transferred as a stream signal, and the stream signal is transferred after being converted to two-dimensional VLC when the DCT coefficients are rearranged and coding is performed using the two-dimensional VLC table. When the stream signal has a particularly large "run", which is the number of "0" coefficients before the non-zero coefficient, the coefficient often does not contain valid image information. Makes the non-zero coefficient of such a run be cut (erased).

The number of coefficients to be cut is determined according to the picture type. For example, B pictures are not used for predicting a decoded image.
The coefficients are cut so that many macro blocks are generated.

However, in the case of a P picture, the following P and B
Since the decoded image is used for predicting a picture, DC
When the T coefficient is cut, an error signal is generated due to the occurrence of a prediction error due to a mismatch between the prediction images on the encoding side and the re-encoding / decoding side during that period. The propagation of the prediction error is suppressed by preventing the number of macro blocks from being increased.

In this way, by generating the updated image data in which the difference image data between the image data relating to the pixel block and the reference frame image for motion compensation prediction decoding is deleted, a stream signal having a reduced code amount is generated. Convert.

Then, the signal processing is performed on D
A stream signal is generated based on the CT coefficients, and a CBP (coded block pattern: Coded Block) related to a block in which DCT coefficients are all “0” in a coefficient operation unit in the generated stream signal. Block pattern) needs to be changed accordingly, so its D
Information on the CT coefficient is supplied from the coefficient operation unit 25 to the MB data changing unit 26.

Then, when the DCT coefficients in all six blocks of the macro block are "0", that is, "N"
A macroblock in the state of “ot Coded” determines that the macroblock is a skipped macroblock,
The determined information is transferred as a stream signal, and the DCT coefficient information therefor is transferred to the MV data determination unit 24.
Supplied to

Then, in the MV data judgment section 24,
"No MC" determination for skip macroblock determination is performed. The determination criteria differ depending on the picture type such as I, P, and B. Next, the determination criteria for each picture type will be described.

The criterion is the case where the motion type of the moving picture signal, that is, the type at the time of performing motion compensation prediction is frame prediction performed on a frame structure coded image, or performed on a field structure coded image. It depends on whether it is the case of field prediction.

The motion type of the field prediction is selected and coding is performed when the image signal to be coded includes information with a lot of motion, and in the case of field prediction, that is, other than frame prediction. In this case, the determination regarding “No MC” for skip / macroblock determination is not performed due to the nature of the moving image signal to be encoded.

Next, the normal determination condition of “No MC” will be described for each picture type. First, when the picture type is a macroblock of an I picture and an intra macroblock of a P or B picture, the determination is not performed even if there is a concealment vector.

If the picture type is a P picture, it is determined that the motion vector is "No MC" when the motion vectors of all the blocks in the intra macroblock are "0".

When the picture type is a B picture, the motion prediction direction is a macroblock immediately before the slice having the same motion vector as the prediction direction such as forward prediction, backward prediction, or bidirectional prediction. When it is the same as the above, it is determined to be "No MC" in the P and B pictures, and the coefficient operation unit 25 determines the macroblock set to "Not Coded" as a skipped macroblock.

For the determination of "No MC" other than these cases, the determination of the "No MC" mode is performed only in the case of a P picture, and the determination of a skip macro block is particularly performed for a B picture. Do not do.

In this way, skipped macroblocks are determined. The skipped macroblocks are determined in the case where the motion vectors and the prediction directions of those macroblocks are completely the same, except for those macroblocks. Even if the motion vectors are slightly different from each other, if the following condition is satisfied, it is determined as "No MC" so that a larger number of skipped macroblocks after rate conversion can be generated.

Next, an additional determination condition for generating a larger number of skipped macroblocks will be described.

The first additional determination condition is that the coefficient operation unit 2
This is for the macroblock designated as “Not Coded” in 5. FIG. 12 shows and describes a macroblock when addition determination is made as “Not Coded”.

In FIG. 10, the arrangement of macroblocks constituting a picture image is shown, and the macroblocks indicated by diagonal lines indicate image data that is symmetrical for "Not Coded" addition determination.

The macroblock which is symmetrical to the “Not Coded” addition determination is a macroblock adjacent to the left in the same slice and a macroblock in the immediately higher slice located immediately above the macroblock. When there is a relationship, an additional determination as "Not Coded" is made.

That is, this is a case where the respective macroblocks on the left side and immediately above are subjected to frame structure coding, and the first motion block having the same motion type, such as the motion prediction vector of the frame image being the same. In the second case in which the prediction directions match in the picture of the B picture, and the difference between the motion vector given to the macroblock adjacent to the left and the macroblock immediately above and the motion vector of the macroblock is ± In the third case, which is within 0.5 pixel,
And in the case of a P picture, each component of the motion vector is
This is the fourth case where the pixel is located immediately to the left, immediately above, and all within ± 0.5 pixel.

When the conditions of the first to fourth cases are satisfied, an additional determination is made that the macroblock is "No MC", that is, a skip macroblock.

As in the case of the coefficient cut in the coefficient operation unit 25, such an addition determination is made so that the addition determination of “No MC” is not performed for the P picture, thereby preventing the propagation of the prediction error. It can be suppressed.

Information on the skipped macroblock or the macroblock determined as “No MC” of the P picture obtained by the MV data determination unit 24 in this manner is supplied to the MB data change unit 26. You.

In the MB data changing unit 26, the information of the block in which the DCT coefficients are all “0” in the coefficient operation unit 25, and the skipped macro block or “No MC” is determined in the MV data determination unit 24. Macroblock information and information on the value of the quantization scale supplied from the code amount control unit 23 are supplied, and based on the supplied information, the DC in the slice layer of the bit stream or lower is used.
The VLC data other than the T coefficient is changed. Next, the change of the VLC data in the MB data changing unit 26 will be described.

First, in the stream data relating to the macroblock determined to be a skipped macroblock by the MV data determination unit 24, all data below the macroblock layer are deleted, and the MBA temporarily stored in the MBA memory 27 is deleted. "1" in the (macro block address) information
Is added.

Then, in the macroblock encoded without being skipped, MBA information obtained by adding the number of skipped macroblocks is obtained, and the obtained macroblock address increment information is added to the new MBA information.
It is encoded as information to obtain a modified encoded signal.

Next, for a macroblock determined to be "No MC" in a P picture, an MBT (macro block typ.)
The value of e) is changed from a P picture to an I picture, and information on the motion type and the motion vector is deleted.

For the block in which all of the DCT coefficients have become "0", the data of the corresponding CBP is changed. For example, for a “Not Coded” macroblock in which the DCT coefficients of all blocks have become “0”, the MBT
Are changed, and the CBP and the DCT type in the case of frame structure coding are deleted.

Then, for the macroblock whose quantization scale used in the DCT transform processing has been updated,
After the updated quantization scale is converted into a quantization scale code by a predetermined code table, the head of the slice layer included in the macroblock and the quantization scale recording position of the macroblock whose quantization scale is updated are updated. , The data of the corresponding quantized scale code is updated and transmitted.

[0117] The quantization scale code may be either a macroblock whose quantization scale is updated before rate conversion is not updated after rate conversion or vice versa. In these cases, The MBT is simultaneously changed according to the state of the update.

It is to be noted that, for a macroblock designated as “Not Coded”, the quantization scale information relating to the macroblock is not required, and thus the scale information arranged in the bit stream is not required.

In this way, information on the macroblock to be coded is obtained to generate header information in the macroblock layer, and header information in the block layer is generated following the macroblock layer. .

The data of the requantized DCT coefficient, which is the header information of the block layer, is obtained by converting the requantized DCT coefficient obtained by operating the coefficient operating section 25 into the two-dimensional VLC section 2.
8 and obtained as two-dimensional VLC data.

The DCT coefficient obtained by performing the two-dimensional VLC and the data other than the DCT coefficient obtained by being changed by the MB data changing unit 26 are obtained by the data combining unit 29 based on the syntax of MPEG-2. The signal is recombined, and the signal obtained by the recombination is supplied to the header combining unit 15.

In the header combining section 15, only the updated new bit rate value of the header data temporarily stored in the header data storage section 14 is replaced with the converted value and is changed by the two-dimensional VLC section 28. The data is subjected to long coding, combined with the converted data obtained by combining the data in the data combining unit 29, and supplied to the re-MUX unit 17, where the re-MUX unit 1
In 7, a bit stream signal combined with a signal portion other than the image coded signal supplied from the DEMUX unit 11 and obtained is provided as an output signal of the image coding rate conversion device 10.

The configuration of the image coding rate conversion apparatus according to the first embodiment in which the rate conversion is performed by inverse quantization and requantization and the operation of the apparatus have been described above.
Next, an image coded data rate conversion device according to a second embodiment in which rate conversion is performed without using inverse quantization and requantization will be described.

FIG. 13 shows the configuration of an image coded data rate converter according to the second embodiment. That is, the image coded data rate conversion device performs the rate conversion by operating the DCT coefficient portion without performing the inverse quantization / requantization.

That is, the image coding rate conversion device 10a according to the second embodiment shown in the figure is different from the image coding rate conversion device 10 according to the first embodiment in the image rate conversion unit 2a.
0a, the configuration is different, and other configurations having the same function are denoted by the same reference numerals.

Then, the image rate conversion unit 20a
CT coefficient separation unit 31, code amount control unit 23a, MV data determination unit 24, coefficient operation unit 25a, MB data change unit 2
6, an MBA memory 27, and a DCT coefficient combining unit 32.

The image coding rate converter 10a according to the second embodiment is different from the image coding rate converter 10 according to the first embodiment in the operation of the image rate converter 20a, that is, the DCT coefficient separator 31. , Coefficient operation unit 25a, D
Only the operation of the CT coefficient combining unit 32 and the operation of the code amount control unit 23a are different, and the operation of the image encoding rate conversion device 10a will be described with other operations being simplified.

The MPEG-2 stream supplied to the image coding rate conversion device 10a is
Is supplied to the DCT coefficient separating unit 31 which is one of the encoded signals from which the header data portion is separated, and the DCT coefficient separating unit 31 separates the DCT coefficient portion from the image data portion and obtains it. , The resulting D
The data of the CT coefficient portion is supplied to the coefficient operation unit 25a.

The data portion other than the DCT coefficient portion of the image data portion is supplied to the MB data changing portion 26, and the motion vector data included in the data portion is supplied to the MV data determining portion 24.

The other header data portion separated by the header separation unit 13 is supplied to the code amount control unit 23a, where the bit amount information before conversion, the target bit rate information after conversion, The code amount information of each image before and after conversion supplied from the input code amount counter 12 and the output code amount counter 16, the code amount information before and after rate conversion of each block counted by the coefficient operation unit 25a, and If necessary, quantization scale code information is supplied, and the code amount is controlled by a predetermined method based on the supplied information.

In the code amount control method, after the target code amount for each image is determined, the target code amount is
Divide by the number of macroblocks included per frame, determine a target code amount per macroblock based on the code amount obtained by division, and assign a target code amount to the macroblock based on the determined code amount per macroblock. A target code amount is assigned to each of the six blocks included.

The target code amount for each block thus allocated is supplied to the coefficient operation unit 25a, and the coefficient operation unit 25a calculates the target code amount based on the allocated code amount.
The coefficient of each corresponding block is controlled, and the coefficient operation unit 25 sets the code amount of each block to the target code amount.
The coefficient operation at a is performed.

In the code amount control by another method, the bit rate ratio of the portion related to the DCT coefficient code amount of the converted target code amount with respect to the code amount before the rate conversion for each block is obtained. The determined bit rate ratio is multiplied by the pre-conversion code amount to determine a target code amount after rate conversion for each block, and the determined post-conversion target code amount information is supplied to the coefficient operation unit 25a. The operation of the DCT coefficient portion is performed as obtained.

The DC in the coefficient operating section 25a at that time is
In the operation of the T coefficient portion, when the target code amount after rate conversion for each block is larger than the code amount before conversion, the coefficient operation process is not performed, but the converted bit rate signal equal to the target value is not processed. For example, when it is desired to obtain a target transfer rate signal, dummy data is inserted into the image data position of each slice or picture as needed.

Conversely, if the target code amount after rate conversion of each block is smaller than the code amount before conversion, the two-dimensional VLC
Therefore, it is necessary to reduce the data amount of the DCT coefficient portion before the rate conversion, which has been encoded by the above, and perform an operation for obtaining data of the target code amount after the conversion.

In this operation, for example, the two-dimensional VLC code arranged before the EOB is deleted one word at a time by a combination of a run and a level, and the converted target code amount reaches a predetermined value. Sometimes there is a way to stop that deletion.

As another operation method, the two-dimensional V
The DCT coefficient sequence data is obtained by decoding the LC code, the coefficient is cut by replacing a part of the obtained DCT coefficient sequence data with “0”, and the cut DCT coefficient sequence data is re-processed. There is a method for obtaining data of a predetermined converted target code amount by performing two-dimensional VLC coding.

When the data of the converted target code amount is given as a low bit rate value, by increasing the number of coefficients to be replaced with "0" especially in a B picture, the MV data determination unit Is generated.

By these methods, data of a predetermined converted target code amount can be obtained. The header information preceding the obtained converted target code amount data is shown in the first embodiment. Similarly to the above method, if necessary, the picture type, the type of the block, the target bit rate after the rate conversion, and the position and number of coefficients are changed according to the target code amount allocated to the block.

For the block in which the DCT coefficients have all become "0" in the coefficient operation section 25a, the information is transferred to the MB
The data is supplied to the data changing unit 26 to change the CBP. Further, the macroblock that has become “Not Coded” supplies the information to the MV data determination unit 24 to determine a skipped macroblock.

For the macroblock in which the coefficients of all the blocks have become “0” and become “Not Coded”, the prediction direction, the prediction type, and the value of the motion vector are checked, and the “skip” determined in advance by the picture type is checked. If the condition of "macroblock" is met, this macroblock is changed to a skipped macroblock.

Further, when the value of the motion vector is "skip
Even if the condition of the macro block does not completely match, if the value of the macro block is close to the condition of the skipped macro block within a predetermined range and other conditions are matched, the macro block is skipped. Change to

In the macroblock changed to the skipped macroblock in this way, all the codes below the macroblock layer are deleted, and the address information of the macroblock is deleted from the macroblock arranged next to the deleted code. By changing to address information, the number of skipped macroblocks can be increased, and code rate conversion to a low rate can be performed while keeping deterioration of image encoded data occurring at the time of rate conversion small. .

Further, regarding the change to the skipped macroblock, when the value of the DCT coefficient after the rate conversion is within a predetermined range, and when the value of the motion vector is within a predetermined range with respect to the condition of the skipped macroblock. , The change to the skipped macroblock is limited to only the B picture, so that the prediction error caused by the mismatch between the prediction images on the encoding side and the re-encoding / decoding side, which occurs when the change to the skipped macroblock occurs. Growth can be minimized.

As described above, for a skipped macroblock or a macroblock determined to be “No MC” (P picture only), the information is transferred to the MB data changing unit 2.
6 to change the VLC data other than the DCT coefficient.

However, unlike the first embodiment, the value of the quantization scale is not changed by the rate conversion.

Thus, the two-dimensional VLC code of the DCT coefficient part after rate conversion obtained by operating the coefficient operating unit 25a and the data other than the DCT coefficient changed by the MB data changing unit 26 are: , DCT coefficient coupling unit 3
2 is recombined based on the syntax defined in the MPEG-2 standard.

The data obtained by the re-combination is supplied to the header combining unit 15, and the header combining unit 15 applies a bit rate to the header data temporarily stored in the header data storage unit. Is generated and combined with the generated header data, and the combined data is supplied to the re-MUX unit 17, where the data supplied from the DEMUX unit 11 is, for example, A signal that is combined with an encoded signal other than an image, such as an audio signal, and the signal thus combined is supplied from the image encoding rate converter 10a as an MPEG-2 bit stream output signal.

The first and second embodiments for converting the transfer rate without converting the signal of the bit stream encoded based on the MPEG-2 system to the pixel level have been described.

In the rate conversion method performed by these embodiments, the supplied moving image signal in units of frame images is divided into a plurality of image data for each pixel block of, for example, 16 × 16 pixels. A motion vector amount is obtained for each pixel block, and while performing motion compensation prediction based on the obtained motion vector amount, orthogonal transformation is performed on image data of the pixel block by DCT transformation or the like,
The data obtained by the orthogonal transformation is quantized, and the data obtained by the quantization is subjected to variable-length encoding to generate an encoded image signal, and the orthogonal transformation and motion related to the generation of the encoded image signal are performed. Information of coding parameters related to prediction or the like is obtained as coding information, a header signal including the obtained coding information is generated, and the generated coded image signal and header signal are combined to form a first signal. And a data of the obtained bit stream is supplied, and is supplied with the data of the obtained bit stream and is lower than the first transfer rate or different from the first transfer rate. A method of converting the rate of encoded image data obtained by converting the signal into a bit stream signal encoded at a transfer rate of The coded image signal and coding parameter information are separated from the stream signal, and coefficient data for each pixel block obtained by orthogonally transforming the coded image signal is newly transferred based on the obtained coded information. It is obtained as update processing coefficient data subjected to rate conversion processing based on the rate, and when the motion vector amount of the pixel block related to the obtained update processing coefficient data is equal to or less than a predetermined pixel value, or related to the pixel block. When the interval of motion prediction in which image data is used as a reference frame image for motion compensated prediction decoding is small, or when not used as a reference frame image, at least image data or a reference frame image for motion compensated prediction decoding for the pixel block Update including skipped macroblock signal by deleting one of differential image data Generating image data, generating updated coding information based on the generated updated image data, obtaining a header signal containing the generated coding information, and obtaining the obtained header signal and the updated image. Since the data can be combined to generate a bit stream signal at the converted transfer rate, it is necessary to convert the coded signal to an image signal and then re-encode it to convert the transfer rate. The delay time for signal conversion can be reduced in comparison with that, and there is no need to temporarily store an image signal for signal conversion, so that the conversion method is easy, or the configuration of the conversion device is simple, and the coded signal As compared with the conventional method of converting the transfer rate without converting the image into an image signal, a signal relating to the motion compensation prediction included in the header of the bit stream is obtained, and the processing of the DCT coefficient is more skipped. Since a macroblock is generated, a coded signal with little image quality degradation can be obtained even when converting to a coded signal with a particularly low transfer rate.

In the above-described embodiment, the encoding method of the bit stream to be converted is mainly MPEG-2. However, the encoding method is not limited to MPEG-2, and a skip macro block can be generated. And an encoding method having a data structure similar to MPEG-2 such as a macroblock type or CBP, for example, MPEG-1
Scheme, H261 and other schemes, and other MPEG-4, M
The present invention is also applicable to bit streams encoded by PEG-7, MPEG-21, or the like.

The code amount control before and after the rate conversion shown in these examples can be applied to either fixed bit rate control or variable bit rate control.

[0153]

According to the first aspect of the present invention, since the transfer rate can be converted without converting the coded signal to the pixel level and while performing the skip macroblock processing, the image quality is less deteriorated. In addition, there is an effect that it is possible to provide a rate conversion method of image coded data in which code amount control can be easily performed.

According to the second aspect of the present invention, in particular, since the transfer rate of the coded signal for the image data based on the updated coefficient data is converted, the image quality is further reduced in addition to the effect of the first aspect. There is an effect that it is possible to provide a rate conversion method for encoded image data, which is small and can easily control the code amount.

According to the third aspect of the invention, the transfer rate of the coded signal is converted by using the updated quantization scale. Therefore, in addition to the effect of the second aspect, the image quality is further reduced. In addition, there is an effect that it is possible to provide a rate conversion method of image coded data in which code amount control can be easily performed.

According to the fourth aspect of the present invention, in particular, the deletion of image data related to a pixel block is performed in order from the higher-order coefficient data obtained by orthogonally transforming the pixel block. In addition to the effect of item 1, there is an effect that it is possible to provide a rate conversion method of image encoded data in which image quality deterioration is further reduced and code amount control can be easily performed.

According to the fifth aspect of the present invention, particularly for image types not used as reference frame images,
2. In addition to the effect of claim 1, the motion vector amount of the pixel block is set to be larger than the predetermined value so that the image data relating to the pixel block is deleted. There is an effect that it is possible to provide a method of converting the rate of encoded image data in which the amount can be easily controlled.

According to the sixth aspect of the present invention, since the transfer rate can be converted without converting the coded signal to the pixel level and while performing the skip macroblock processing, the image quality is less deteriorated. In addition, there is an effect that it is possible to provide a configuration of an image coding data rate conversion device capable of easily controlling the code amount.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an image coding rate conversion device according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram of an MPEG-2 encoding device.

FIG. 3 is a diagram illustrating a structure of a picture type related to motion compensation prediction in the MPEG-2 encoding method.

FIG. 4 is a diagram illustrating a structure of pixel data relating to transform coding of the MPEG-2 coding method.

FIG. 5 is a diagram showing a data structure of a bit stream transmitted by the MPEG-2 system.

FIG. 6 is a diagram showing a data structure in a macroblock layer encoded according to the MPEG-2 system.

FIG. 7 shows a macroblock type VLC table for an I picture encoded according to the MPEG-2 system.

FIG. 8 shows a macroblock type VLC table for a P picture coded according to the MPEG-2 system.

FIG. 9 shows a macroblock type VLC table for a B picture encoded according to the MPEG-2 system.

FIG. 10 is a diagram showing a data structure in a block layer encoded by the MPEG-2 system.

FIG. 11 is a diagram illustrating a configuration of an image coding rate conversion device according to a first embodiment of the present invention.

FIG. 12 is a diagram for describing determination of an uncoded macroblock according to the embodiment of the present invention.

FIG. 13 is a diagram showing a configuration of an image coding rate conversion device according to a second embodiment of the present invention.

FIG. 14 is a diagram showing a configuration of a rate conversion device in a conventional example.

[Explanation of symbols]

 10, 10a Image coding rate conversion device 11 DEMUX unit 12 Input code amount counter 13 Header separation unit 14 Header data storage unit 15 Header combining unit 16 Output code amount counter 17 Re-MUX unit 20, 20a Image rate conversion unit 21 Variable length decoding Separation unit 22 Inverse quantization / requantization unit 23, 23a Code amount control unit 24 MV data determination unit 25, 25a Coefficient operation unit 26 MB data change unit 27 MBA memory 28 Two-dimensional VLC unit 29 Data combination unit 31 DCT coefficient Separation unit 32 DCT coefficient combining unit 60 MPEG-2 encoder 61 Subtractor 62 DCT unit 63 Quantizer 64 Code amount controller 65 Variable length encoder 66 Buffer 71 Inverse quantizer 72 IDCT unit 73 Adder 74 Frame memory 75 Motion compensation predictor 81 data separation circuit 82 inverse VL C circuit 83 Inverse quantizer 84 Bit rate control circuit 85 Quantizer 86 VLC circuit 87 Coupling circuit 88 Buffer circuit

Continued on front page F-term (reference) BD01

Claims (6)

[Claims] 1. A moving image signal is divided into a plurality of image data for each pixel block of a predetermined size, a motion vector amount is obtained for each of the divided pixel blocks, and a motion vector amount is calculated based on the obtained motion vector amount. An encoded image signal is obtained by performing orthogonal transformation of the image data of the pixel block while performing compensation prediction, quantizing the data obtained by the orthogonal transformation, and performing variable length coding on the data obtained by the quantization. , And obtains information of coding parameters related to generation of the coded image signal as coding information, generates a header signal including the obtained coding information, and generates the generated coded image signal. And the header signal are combined to obtain first encoded data compressed and encoded at the first transfer rate, and the obtained first encoded data is supplied;
A rate conversion method for image encoded data obtained by converting the first encoded data into second encoded data compressed and encoded at a second transfer rate, comprising: A first step of obtaining the encoded image signal and the encoded information, based on the encoded information obtained by the first step,
Image data for each pixel block obtained by orthogonally transforming the coded image signal is obtained, and when the motion vector amount of the pixel block related to the obtained image data is equal to or less than a predetermined value, or At least one of the image data and the difference image data from the reference frame image for motion compensation prediction decoding when the interval of the motion prediction in which the image data to be used as the reference frame image for motion compensation prediction decoding is equal to or less than the predetermined number of frames. A second step of generating updated image data in which is deleted, and generating encoded information relating to an encoded image signal updated based on the updated image data generated by the second step. A third step of obtaining a header signal including the encoded information, the header signal obtained in the third step,
And a fourth step of combining the updated image data generated in step (b) to obtain the second coded data. 2. An updated image data in the second step is a rate conversion of coefficient data for each pixel block obtained by orthogonally transforming an image signal relating to the image data based on the second transfer rate. 2. The method according to claim 1, wherein deletion processing is performed on the image data generated based on the processed update coefficient data. 3. The update processing coefficient data is subjected to inverse quantization using the quantization scale used to obtain the coefficient data, and the image data obtained by the inverse quantization is used to obtain second encoded data. 3. The method according to claim 2, wherein the rate is obtained by performing requantization using the updated updated quantization scale. 4. The method according to claim 3, wherein the deletion of the image data relating to the pixel block in the third step is performed by sequentially reducing the coefficient data of a higher order obtained by orthogonally transforming the pixel block. 2. The method for converting encoded image data according to claim 1. 5. The method according to claim 3, wherein the deleting of the image data in the third step is performed when the image data relating to the pixel block is of an image type not used as a reference frame image. 2. The rate of encoded image data according to claim 1, wherein a predetermined value for a non-reference image set to be larger than the value is set, and updated image data is generated by deleting image data relating to the pixel block. Conversion method. 6. A moving image signal is divided into a plurality of image data for each pixel block of a predetermined size, a motion vector amount is obtained for each of the divided pixel blocks, and a motion vector amount is calculated based on the obtained motion vector amount. An encoded image signal is obtained by performing orthogonal transformation of the image data of the pixel block while performing compensation prediction, quantizing the data obtained by the orthogonal transformation, and performing variable length coding on the data obtained by the quantization. , And obtains information of coding parameters related to generation of the coded image signal as coding information, generates a header signal including the obtained coding information, and generates the generated coded image signal. And the header signal are combined to obtain first encoded data compressed and encoded at the first transfer rate, and the obtained first encoded data is supplied;
An image coded data rate conversion device obtained by converting the first coded data into second coded data compressed and coded at a second transfer rate, wherein the first coded data is A coded image signal and signal separation means for obtaining the coded information; and a motion vector amount of a pixel block obtained by orthogonally transforming the coded image signal is equal to or less than a predetermined value, or At least one of the image data and the difference image data from the reference frame image for motion compensation prediction decoding when the interval of the motion prediction in which the image data to be used as the reference frame image for motion compensation prediction decoding is equal to or less than the predetermined number of frames. Image data converting means for generating updated image data from which the image data has been deleted, and updating based on the updated image data generated by the image data converting means. Signal updating means for generating encoded information relating to the encoded image signal obtained, and obtaining a header signal including the generated encoded information, a header signal obtained by the header signal updating means, and the image data An image coded data rate conversion apparatus comprising: signal combination means for combining the updated image data generated by the conversion means to obtain the second coded data.