JP3358620B2 - Image encoding method and image encoding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding method and an image encoding apparatus, and more particularly to a system for encoding and recording moving image video signals on an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape. And a system for transmitting a video signal of a moving image via a transmission path.

[0002]

2. Description of the Related Art Conventionally, a system for transmitting a video signal of a moving image to a remote place, such as a video conference system and a video telephone system, and a video signal of a moving image are recorded on an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape. In a system or the like for reproducing a video signal of a recorded moving image, in order to efficiently use a transmission path (or an image recording medium), a video signal is so-called utilizing a line correlation or a frame correlation of the video signal. High-efficiency coding is performed to reduce the redundancy in the space axis direction and the time axis direction and transmit only significant information, thereby improving transmission efficiency.

For example, in an encoding process in the spatial axis direction (hereinafter referred to as an intra-frame encoding process), as shown in FIG.
For example, a line correlation of a video signal is used.
Each image P constituting a moving image at 1, t2, t3,.
When trying to transmit C1, PC2, PC3 ...
The image data to be transmitted is, for example, 1 in the same scanning line.
Data compression is performed by two-dimensional encoding or by dividing an image into a plurality of blocks and two-dimensionally encoding the image data of each block, thereby improving transmission efficiency.

In the encoding process in the time axis direction (hereinafter referred to as inter-frame encoding process), for example, so-called predictive encoding is performed using inter-frame correlation of a video signal, that is, as shown in FIG. Matching image PCl and PC
2, image data PC1 which is a difference (a so-called prediction error) of the image data of each corresponding pixel between PC2 and PC3.
2, PC23..., And these image data PC1
2, data is compressed by transmitting the PC 23, and the transmission efficiency is improved.

[0005] Thus, the images PC1, PC2, PC3
The video signal can be transmitted with a much smaller data amount than when all the image data is transmitted.

In the above-described predictive coding in the inter-frame coding process, for example, motion compensation prediction is used for each macroblock in order to further increase the efficiency. That is, for example, when a person in the center of the screen moves, the movement of a moving object on the screen is detected, and the position of the image data used for prediction in the image preceding by the movement is corrected to perform the prediction. By performing the encoding, the encoding efficiency can be improved. However, even now, much data must be sent to the part where the object moves and appears from behind. Therefore, the coding efficiency can be further improved by performing the motion compensation prediction not only in the above-mentioned forward direction but also in the backward direction or in a combination of both.

Specifically, as shown in FIG. 8A, frame data F0, F1,... Of the 0th, 1st, 2nd, 3rd,...
In the macroblocks F2, F3,..., When there is a change in the image as represented by the motion vectors X0, X1, X2, X3,. Every second (for example, one frame), that is, the second, fourth,..., Frames are designated as interpolation frames.
As shown in B, transmission interpolation frame data F2X, F4X... Are generated by predetermined interpolation frame processing. In addition, the frame data F
, F3... Are subjected to a predetermined encoding process to generate transmission non-interpolated frame data F1X, F3X.

For example, motion-compensated frame data F
3 and the frame data F2, the difference SP2 (prediction error), the motion-compensated frame data F1 and the frame data F2
, The motion-compensated frame data F1, F2
Then, a difference SP4 between the frame data and the frame data F2 obtained by performing the interpolation process on No. 3 is obtained for each macroblock, and the difference between the macroblock SP1 of the frame data F2 and these differences is compared. And these data SP
1 to SP4, the data with the smallest data generation amount is referred to as transmission interpolation data F2X in macroblock units, and so on.
... is generated. Also, for example, the non-interpolated frame data F1, F3,... Are subjected to, for example, DCT conversion processing, variable-length coding processing, etc. to generate transmission non-interpolated frame data F1X, F3X.

The transmission non-interpolated frame data F1X, F3X...
.. Together with the data of the motion vectors X0, X1, X3,... As transmission data DATA to the device on the receiving side.

On the other hand, the apparatus on the receiving side transmits transmitted data DATA (transmitted non-interpolated frame data F1X, F3X
,..., Transmission interpolation data F2X, F4X,..., Motion vectors X0, X1, X3,. , F2, F3,... As a result, the coding efficiency can be further improved by performing the motion compensation prediction not only in the forward direction but also in the backward direction or in a combination of the two directions.

Here, an image encoding apparatus and an image decoding apparatus having the above-described functions will be described.

As shown in FIG. 9, the image encoding apparatus 60 includes a pre-processing circuit 61 for separating an input video signal VD into a luminance signal and a color difference signal, a luminance signal from the pre-processing circuit 61,
Analog / digital (hereinafter referred to as A / D) conversion circuits 62a and 62 for converting color difference signals into digital signals, respectively.
2b, a frame memory group 63 for storing luminance data and color difference data (hereinafter referred to as image data) from the A / D conversion circuits 62a and 62b, and a frame memory group 63
A format conversion circuit 64 for reading out image data from the format conversion circuit 64 in accordance with a block format, and an encoder 65 for encoding the image data of the block from the format conversion circuit 64 with high efficiency.

The pre-processing circuit 61 separates the input video signal VD into a luminance signal and a chrominance signal.
2a and 62b convert the luminance signal and the chrominance signal into 8-bit luminance data and chrominance data, respectively, and the frame memory group 63 stores these luminance data and chrominance data.

The format conversion circuit 64 converts the image data (luminance data,
Color difference data) according to a block format, and the encoder 65 encodes the read image data by predetermined high-efficiency encoding, and outputs a bit stream.

The bit stream is supplied to an image decoding device 80 via a transmission path or a transmission medium 70 including an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape.

As shown in FIG. 9 described above, the image decoding apparatus 80 includes a decoder 81 corresponding to the encoder 65.
A format conversion circuit 82 for converting the image data reproduced by the decoder 81 into a frame format,
A frame memory group 83 for storing image data from the format conversion circuit 82; D / A conversion circuits 84a and 84b for converting luminance data and color difference data read from the frame memory group 83 into analog signals; A post-processing circuit 85 that mixes the luminance signal and the color difference signals from the conversion circuits 84a and 84b to generate an output video signal.

The decoder 81 includes an encoder 65
The bit stream is decoded by decoding corresponding to the high-efficiency encoding to reproduce the image data in the block format, and the format conversion circuit 82 converts the image data into the frame format, and
3 is stored.

The D / A conversion circuits 84a and 84b convert the luminance data and chrominance data read from the frame memory group 83 into a luminance signal and a chrominance signal, respectively. The signals are mixed to generate an output video signal.

Specifically, the preprocessing circuit 61 and the A / D conversion circuits 62a and 62b convert the luminance signal and the color difference signal into digital signals as described above, The number of pixels is の of the luminance signal
After reducing the amount of data so that
The obtained luminance data and color difference data are stored in a frame memory group 6
Supply 3

The luminance data and the color difference data are read from the frame memory group 63 in accordance with the block format as described above. That is, for example, image data for one frame is divided into N slices as shown in FIG. 10A, and each slice includes M macroblocks as shown in FIG. As shown in FIG. 10C, the block is a block unit composed of 8 × 8 pixels, and luminance data Y1, Y2, Y3, and Y4 of four luminance blocks adjacent vertically, horizontally, and
The color difference data includes color difference data Cb and Cr of a color difference block composed of 8 × 8 pixels in a range corresponding to these four luminance blocks. Then, from the frame memory group 63, image data continues in units of macroblocks in the slice, and Y1, Y2, Y3, Y4, Cb, C
The luminance data and the color difference data are read so as to be continuous in the order of r. The image data read according to the block format in this manner is supplied to the encoder 65.

The encoder 65, as shown in FIG.
A motion vector detection circuit 101 is provided. The motion vector detection circuit 101 detects a motion vector of image data supplied in a block format on a macroblock basis. That is, the motion vector detection circuit 101 detects the motion vector of the current reference image in macroblock units using the front original image and / or the rear original image stored in the frame memory group 63. Here, in the detection of the motion vector, the motion vector in which the sum of the absolute values of the inter-frame differences in the macroblock unit is minimized is set as the motion vector. Then, the detected motion vector is supplied to the motion compensation circuit 113 and the like, and the sum of absolute values of the inter-frame differences in macroblock units is supplied to the intra-frame / forward / backward / bidirectional prediction determination circuit 103.

The intra / forward / backward / bidirectional prediction determination circuit 103 determines the prediction mode of the reference block based on this value, and, based on the determined prediction mode, the intra / forward prediction frame for each macroblock. The prediction encoding circuit 104 is controlled so as to switch between / backward / bidirectional prediction. Then, the predictive encoding circuit 104
a, 104b, 104c, and a changeover switch 104d. The input image data itself is used in the intra-frame coding mode, and the difference (pixel) of the input image data with respect to each prediction image in the forward / backward / bidirectional prediction mode. The data is supplied to the DCT circuit 105.

The DCT circuit 105 uses the two-dimensional correlation of the video signal to perform DCT on the input image data or difference data in block units and supplies the obtained coefficient data to the quantization circuit 106.

The quantization circuit 106 quantizes the coefficient data using a quantization step size (quantization scale) determined for each macroblock or slice, and encodes the obtained quantized data into a variable length code (VLC: Variable Length).
(Code) circuit 107 and an inverse quantization circuit 108. By the way, the quantization step size used for the quantization is determined by feeding back the remaining buffer amount of the transmission buffer memory 109, which will be described later, so that the transmission buffer memory 109 does not fail. The quantization step size is also determined by the VLC circuit. 107 and inverse quantization circuit 1
08.

The VLC circuit 107 performs variable length coding on the quantized data together with the quantization step size, the prediction mode, and the motion vector, and supplies the data to the transmission buffer memory 109 as transmission data.

The transmission buffer memory 109 stores the transmission data once, reads it out at a constant bit rate, smoothes the transmission data and outputs it as a bit stream, and outputs the bit stream according to the amount of residual data remaining in the memory. Then, the quantization control signal in macroblock units is fed back to the quantization circuit 106 to control the quantization step size. Thereby, the transmission buffer memory 109
Adjusts the amount of data generated as a bit stream and maintains an appropriate amount of data in the memory (a data amount that does not cause overflow or underflow). For example, when the remaining amount of data in the transmission buffer memory 109 increases to the allowable upper limit, the transmission buffer memory 1
In step 09, the data amount of the quantized data is reduced by increasing the quantization step size of the quantization circuit 106 by the quantization control signal. On the other hand, when the remaining amount of data in the transmission buffer memory 109 decreases to the permissible lower limit, the transmission buffer memory 109 reduces the quantization step size of the quantization circuit 106 by the quantization control signal, thereby obtaining the data of the quantized data. Increase volume.

As described above, the bit stream output from the buffer memory 109 is transmitted at a constant bit rate to the transmission path and the transmission medium 70 composed of an image recording medium such as an optical disk, a magnetic disk, and a magnetic tape as described above. The image is supplied to the image decoding apparatus 80 via

On the other hand, the inverse quantization circuit 108 inversely quantizes the quantized data supplied from the quantization circuit 106, and coefficient data (quantization distortion is added thereto) corresponding to the output of the DCT circuit 105 described above. ) Is reproduced, and the coefficient data is subjected to inverse discrete cosine transform (hereinafter, IDCT: Inverse Discrete C).
osine transform).

The IDCT circuit 110 converts the coefficient data into an ID
CT conversion and reproduces image data corresponding to the input image data in the intra-frame encoding mode, and reproduces difference data corresponding to the output of the prediction encoding circuit 104 in the forward / backward / bidirectional prediction mode. 111.
In the forward / backward / bidirectional prediction mode, the addition circuit 111 is supplied with motion-compensated predicted image data from a motion compensation circuit 113 described later, and adds the motion-compensated predicted image data and difference data. By doing so, the image data corresponding to the input image data is reproduced.

The image data thus reproduced is stored in the frame memory 112. That is, the inverse quantization circuit 108 to the addition circuit 111 constitute a local decoding circuit, and the quantization circuit 1
The quantized data output from 06 is locally decoded, and the obtained decoded image is written to the frame memory 112 as a forward predicted image or a backward predicted image. Frame memory 1
Numeral 12 is composed of a plurality of frame memories, the bank switching of the frame memories is performed, and a single frame is output as forward prediction image data or backward prediction image data depending on the image to be encoded. . In the case of bidirectional prediction, forward predicted image data and backward predicted image data are averaged and output, for example. These predicted image data are exactly the same images as the images reproduced by the decoder 81 described later, and the next processed image is subjected to forward / backward / bidirectional prediction encoding based on this predicted image.

That is, the image data read from the frame memory 112 is supplied to the motion compensation circuit 113,
This motion compensation circuit 113 calculates
The motion compensation is performed on the prediction image data, and the motion compensated prediction image data is added to the prediction encoding circuit 104 and the addition circuit 111.
To supply.

Next, the decoder 81 will be described.

A bit stream is input to the decoder 81 via the transmission medium 70. This bit stream is input to a variable length decoding (hereinafter referred to as IVLC) circuit 202 via a reception buffer 201 as shown in FIG. The IVLC circuit 202 reproduces quantized data, a motion vector, a prediction mode, a quantization step size, and the like from the bit stream. These quantization data and quantization step size are supplied to the inverse quantization circuit 203,
The motion vector is supplied to the motion compensation circuit 207, and the prediction mode is supplied to the addition circuit 205.

The operations of the inverse quantization circuit 203 to the addition circuit 205 are the same as those of the local decoding circuit of the encoder 65, and the operations of the frame memory group 206 and the motion compensation circuit 207 are the frame memory 112 and the motion compensation circuit of the encoder 65, respectively. The decoding is performed based on the quantization data, the motion vector, the prediction mode, and the quantization step size. As a result, reproduced image data is output from the addition circuit 205.

As described above, in the conventional apparatus, the encoding bit rate of the bit stream generated by the encoder 65 is fixed in accordance with the transfer rate of the transmission medium 70, and under this restriction, the amount of data generation, that is, The quantization step size of the quantization circuit 106 in the encoder 65 has been controlled. In other words, for example, when images with complicated patterns continue, the quantization step size is increased to suppress the amount of data generation, and conversely, when simple patterns continue, the quantization step size is reduced to reduce the data size. By increasing the generation amount, a fixed rate is maintained without causing an overflow or underflow of the buffer memory 109.

Therefore, in the conventional apparatus, when a complicated image is continuous, the quantization step size is increased,
When the image quality is degraded and simple images continue, the quantization step size is reduced, and it is not possible to obtain uniform image quality throughout.

When a bit stream is recorded on an image recording medium having a limited data capacity, in order to prevent an extreme deterioration in image quality of an image having a complicated pattern, the image quality of the complicated image is not impaired. A higher fixed rate must be applied to the whole, resulting in reduced recording time.

[0038]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method, for example, in which images having complicated patterns It is an object of the present invention to provide an image encoding method and an image encoding device capable of obtaining uniform high image quality throughout without increasing the quantization step size unlike the conventional device.

Another object of the present invention is to make it possible to effectively use a limited recording capacity when recording on an image recording medium, to increase the recording time of image data on the image recording medium, Another object of the present invention is to provide an image encoding method and an image encoding device capable of reproducing uniform high-quality image data throughout from an image recording medium.

[0040]

According to an aspect of the present invention, there is provided an image encoding method for encoding input image data, comprising the steps of converting input image data from a plurality of images. Coded for each GOP
Generating the first encoded data for each GOP, and calculating the degree of difficulty of encoding for each GOP based on the data amount of the first encoded data generated in the step of generating the first encoded data. A step of calculating the sum of the encoding difficulty levels of the plurality of GOPs;
A larger amount of code is allocated to each GOP according to the ratio of the total sum of the degree of difficulty of encoding P to GOPs including images having complicated patterns, and to GOPs including images having simple patterns. And calculating the input image data for each GOP as GO
Encoding is performed based on the assigned code amount assigned to each P itself to generate second encoded data, and the data amount of the second encoded data for each GOP becomes the assigned code amount for each GOP. And

An image encoding apparatus according to the present invention is an image encoding apparatus for encoding input image data, wherein the input image data for a plurality of GOPs including a plurality of images is encoded using a fixed quantization step size. A first encoding unit that quantizes to generate first encoded data; and an encoding unit that encodes each GOP based on a data amount of the first encoded data generated by the first encoding unit. The sum of the difficulty level and the total difficulty level of the encoding of the plurality of GOPs is detected, and the allocated code amount allocated to each GOP itself according to the ratio of the total difficulty level of the encoding level of the GOPs and the total level of the encoding difficulty level of the multiple GOPs Encoding control means for calculating a large number of GOPs for a GOP including a complex image and a small number of GOPs for a GOP including a simple image, and input image data for each GOP. , And encoding based on the assigned code amount assigned to each OP itself to generate second coded data, the data amount of the second encoded data of each GOP is GOP
And a second encoding unit for setting the assigned code amount for each.

According to the image encoding method of the present invention, in an image encoding method for encoding input image data, input image data of a plurality of images is encoded to generate first encoded data for each image. Determining the sum of the difficulty of encoding for each image and the difficulty of a plurality of images based on the data amount of the first encoded data generated in the step of generating the first encoded data. And the amount of code assigned to each image itself according to the ratio of the degree of difficulty of encoding for each image to the sum of the degree of difficulty of encoding a plurality of images. Calculating the image data so as to be less allocated to a simple image, and coding the input image data for each image based on the allocated code amount allocated to each image itself,
In which the data amount of the second encoded data for each image becomes the allocated code amount for each image.

An image coding apparatus according to the present invention is an image coding apparatus for coding input image data, wherein the first coding method generates a first coded data by coding a plurality of input image data. Means for calculating the sum of the difficulty of encoding for each image and the difficulty of encoding for a plurality of images based on the data amount of the first encoded data generated by the first encoding means; The assigned code amount assigned to each image itself according to the ratio of the difficulty of encoding for each image and the sum of the difficulty of encoding of a plurality of images, a large amount is assigned to an image with a complicated pattern, and the pattern is simple. Encoding control means for calculating so as to be less allocated to the image; and input image data for each image, which is encoded based on the assigned code amount assigned to each image itself, to form second encoded data. Generate
A second encoding unit that makes the data amount of the second encoded data for each image equal to the allocated code amount for each image.

According to the image encoding method of the present invention, in the image encoding method for encoding the input image data, a step of selecting a prediction mode of each of a plurality of images represented by the input image data; According to the prediction mode,
A step of encoding input image data of a plurality of images to generate first encoded data for each pixel, and a data amount of the first encoded data generated in the step of generating the first encoded data Calculating the sum of the degree of difficulty of encoding for each image and the degree of difficulty of a plurality of images, based on the ratio of the degree of difficulty of encoding for each image and the sum of the degree of difficulty of a plurality of images. Calculating a code amount to be allocated to the image itself, and encoding the input image data for each image based on the code amount allocated to the image itself using a prediction mode, Generating encoded data so that the data amount of the second encoded data for each image becomes the allocated code amount for each image.

An image coding apparatus according to the present invention is an image coding apparatus for coding input image data representing a plurality of images, the prediction method for selecting a prediction mode of each of a plurality of images represented by the input image data. A determination unit configured to encode input image data of a plurality of images according to a selected prediction mode to generate first encoded data for each pixel;
And the sum of the degree of difficulty of encoding for each image and the degree of difficulty of encoding a plurality of images based on the data amount of the first encoded data generated by the first encoding means. Asked,
Encoding control means for calculating an assigned code amount to be assigned to each image itself based on a ratio of a difficulty of encoding of each image and a total of difficulty of encoding a plurality of images; and input image data of each image. Is encoded using the prediction mode and based on the assigned code amount assigned to each image itself,
A second encoding unit configured to generate second encoded data and to make a data amount of the second encoded data for each image equal to an assigned code amount for each image.

In the image coding method according to the present invention, in the image coding method for coding input image data, a step of detecting a motion vector for each macroblock of a plurality of images represented by the input image data Encoding the input image data of a plurality of images using a motion vector to generate first encoded data for each image; and generating the first encoded data in the step of generating the first encoded data. Calculating the sum of the degree of difficulty of encoding for each image and the degree of difficulty of a plurality of images, based on the data amount of the encoded data, and the sum of the degree of difficulty of encoding for each image and the degree of difficulty of a plurality of images. Calculating the amount of code to be allocated to each image based on the ratio of the images, and using the motion vector to allocate the input image data for each image and the allocation allocated to each image itself. Based on the issue amount, by coding,
Generating second encoded data so that the data amount of the second encoded data for each image becomes the allocated code amount for each image.

An image coding apparatus according to the present invention is an image coding apparatus for coding input image data representing a plurality of images, wherein each of the macroblocks of the plurality of images represented by the input image data has a motion. Motion vector detecting means for detecting a vector, and input image data of a plurality of images,
A first encoding unit that encodes using a motion vector to generate first encoded data for each image; and a first encoding unit that generates the first encoded data for each image based on a data amount of the first encoded data generated by the first encoding unit. The sum of the degree of difficulty of encoding of each image and the degree of difficulty of encoding of a plurality of images is calculated based on the ratio of the degree of difficulty of encoding of each image and the sum of the degree of difficulty of encoding of a plurality of images. Encoding control means for calculating an assigned code amount assigned to each image itself, and input image data for each image, using a motion vector, and encoding based on the assigned code amount assigned to each image itself, Generating second encoded data;
A second encoding unit that makes the data amount of the second encoded data for each image equal to the allocated code amount for each image.

[0048]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image encoding method and an image encoding apparatus according to the present invention will be described with reference to the drawings.

An image coding apparatus to which the present invention is applied includes, for example, as shown in FIG. 1, a first coding circuit 10 for coding an input video signal to generate first coded data,
A coding control circuit 30 for obtaining a coding rate for each predetermined time based on a data amount of the first coded data from the coding circuit 10 for each predetermined time and a total amount of usable data;
A second encoding circuit that encodes the input video signal at predetermined time intervals based on the encoding rate from the encoding control circuit to generate second encoded data.

Further, as shown in FIG. 1, the first encoding circuit 10 includes a frame memory group 12 for storing input image data as an input video signal, and an image data group stored in the frame memory group 12. Vector detection circuit 11 for detecting a motion vector of input image data based on
And a frame memory 22 for storing predicted image data;
A motion compensation circuit 23 that performs motion compensation on predicted image data read from the frame memory 22 based on a motion vector from the motion vector detection circuit 11, and a motion compensated predicted image data from the motion compensation circuit 23. hand,
A predictive coding circuit 14 for predictive coding input image data;
A difference or the like which is a prediction error from the prediction coding circuit 14 is coded, for example, a discrete cosine transform (hereinafter, DCT: Discrete Cosin).
e Transform) to generate coefficient data
A quantization circuit 16 that quantizes the coefficient data from the DCT circuit 15 with a fixed quantization step size to generate quantized data, and a variable-length coding of the quantized data from the quantization circuit 16. , A variable length coding (VLC: Variable Length Code) circuit 17 for outputting variable length code data, and an inverse quantization circuit 18 for inversely quantizing the quantized data from the quantization circuit 16 to reproduce coefficient data.
And the coefficient data from the inverse quantization circuit 18, for example, inverse discrete cosine transform (hereinafter referred to as IDCT: Inverse Discrete C)
ID which reproduces the difference by “sine transform”
The difference between the CT circuit 20 and the IDCT circuit 20 and the motion-compensated predicted image data from the motion compensation circuit 23 are added to generate predicted image data for the next input image data, and the predicted image data is stored in the frame memory 22. And an adder circuit 21 for supplying.

As shown in FIG. 1, the second encoding circuit 40 includes a delay unit 43 for delaying the input image data.
And a frame memory 52 for storing predicted image data;
A motion compensation circuit 53 for performing motion compensation on the predicted image data read from the frame memory 52 based on the motion vector from the motion vector detection circuit 11;
3, a prediction encoding circuit 44 that predictively encodes the input image data delayed by the delay unit 43 based on the motion-compensated prediction image data, and a difference from the prediction encoding circuit 44. A DCT circuit 45 that performs DCT conversion to generate coefficient data, a quantization scale setting circuit 33 that sets a quantization step size based on an encoding rate from the encoding control circuit 30, and a coefficient data from the DCT circuit 45 A quantization circuit 46 that quantizes with the quantization step size from the quantization scale setting circuit 33 to generate quantized data, and a variable length code of the quantized data from the quantization circuit 46 to convert the variable length code data A VLC circuit 47 for outputting, a transmission buffer memory 49 for temporarily storing the variable length code data from the VLC circuit 47, and outputting the same at a constant bit rate; An inverse quantization circuit 48 to reproduce coefficient data to inverse quantization to the quantized data from the circuit 46,
The coefficient data from the inverse quantization circuit 48 is decoded, for example, I
An IDCT circuit 50 that performs DCT conversion and reproduces a difference;
An addition circuit 51 that adds the difference from the DCT circuit 50 and the motion-compensated predicted image data from the motion compensation circuit 53 to generate predicted image data for the next input image data, and supplies the predicted image data to the frame memory 52 And

In this image encoding apparatus, the first encoding circuit 10 encodes the input image data,
For example, the encoding control circuit 30 performs a predictive encoding process, a DCT transform process, a quantization process with a fixed quantization step size, and a variable length encoding process. And the total available data determined by the data capacity of the image recording medium 55 such as an optical disk, a magnetic disk, a magnetic tape, or the like, or the bit rate (transfer rate) of the transmission path. After obtaining the coding bit rate, the second coding circuit 40 performs predictive coding processing, DCT transform processing, quantization processing again on the input image data.
When performing variable length coding processing to generate variable length code data as a second bit stream, quantization is performed with a quantization step size based on the coding bit rate.

That is, in this image coding apparatus, as shown in FIG. 2, for example, in step ST1, the quantization circuit 16 of the first coding circuit 10 sets the quantization step size to, for example, 1 and sends it to the DCT circuit 15 from the DCT circuit 15. The supplied coefficient data is quantized to generate quantized data, and the counter 31 of the encoding control circuit 30 performs variable-length coding on the quantized data to obtain variable-length code data (first bit stream). Is counted for a predetermined period of time, for example, for each frame, and a generated code amount indicating the difficulty of encoding is obtained for each frame.

In step ST2, the bit rate calculation circuit 32 determines the degree of difficulty (the amount of generated code) for each frame,
Based on the total amount of usable data, an assigned code amount assigned to each frame is obtained.

In step ST3, the quantization circuit 46 of the second encoding circuit 40 quantizes the coefficient data supplied from the DCT circuit 45 with a quantization step size based on the allocated code amount, and Is generated.

Specifically, the input image data is temporarily stored in the frame memory group 12. Then, the data is read from the frame memory group 12 according to the block format as described in the related art.

The motion vector detecting circuit 11 reads out necessary image data from the frame memory group 12 in units of the above-described macroblocks, and detects a motion vector. That is, the motion vector detection circuit 11
Using the forward original image and / or the backward original image stored in 2, the motion vector of the current reference image is detected in macroblock units. Here, in detecting a motion vector, for example, a motion vector in which the sum of absolute values of differences between frames in a macroblock unit is minimized is set as the motion vector. Then, the detected motion vector is added to the motion compensation circuits 23 and 53.
The sum of the absolute values of the differences between the frames in macroblock units is supplied to the intra-frame / forward / backward / bidirectional prediction determination circuit 13.

The intra / forward / backward / bidirectional prediction determination circuit 13 determines the prediction mode of the reference block based on this value, and, based on the determined prediction mode, the intra / forward / backward prediction for each block. / Controls the prediction encoding circuit 14 to switch between bidirectional prediction.

As shown in FIG. 1, the predictive coding circuit 14 includes adders 14a, 14b, 14c and a changeover switch 14d. In the intra-frame coding mode, the input image data itself is forward / backward. In the case of the bidirectional prediction mode, a difference (hereinafter referred to as difference data) of each pixel of input image data with respect to each predicted image is selected, and the selected data is supplied to the DCT circuit 15.

The DCT circuit 15 uses the two-dimensional correlation of the video signal to perform DCT conversion on the input image data or the difference data supplied from the changeover switch 14d in block units, and outputs the obtained coefficient data to the quantization circuit 16. Supply.

The quantization circuit 16 sets a constant quantization step size, for example,
The coefficient data supplied from the T circuit 15 is quantized, and the obtained quantized data is converted to the VLC circuit 17 and the inverse quantization circuit 1.
8

The VLC circuit 17 performs variable length coding on the quantized data together with the quantization step size, prediction mode, motion vector, etc., and supplies the obtained variable length code data to the coding control circuit 30 as a first bit stream. I do.

As shown in FIG. 1 described above, the encoding control circuit 30 includes a counter 31 for counting the amount of variable-length code data from the VLC circuit 17 for each predetermined time,
And a bit rate calculation circuit 32 for calculating an allocated code amount per predetermined time based on the data amount from 1 and the total amount of usable data. Then, the counter 31 counts the data amount of the first bit stream every predetermined time, for example, every frame, finds the difficulty for each frame, and supplies this difficulty to the bit rate calculation circuit 32.

The bit rate calculation circuit 32 calculates the allocated code amount allocated to each frame, that is, the average coding rate for each frame time, based on the difficulty level for each frame and the total amount of usable data. The code amount is supplied to the quantization scale setting circuit 33 of the second coding circuit 40.

More specifically, the bit rate operation circuit 32
Indicates that the total number of frames is N and the total amount of usable data is B
And then, i (i = 0,1,2 ··· N -1) th frame difficulty of the (generated code amount) and _{d i,} the assigned code amount for the i-th frame as _{b i,} the assigned code Quantity b
If is proportional to the degree of difficulty d _i to indicate _i by the following formula 1,
Data amount B is as shown in the following formula 2, obtained by adding the allocated code quantity b _i of all frames. Note that a is a constant.

[0066]

(Equation 9)

[0067] Accordingly, constant a can be obtained by the following formula 3, and substituting this constant a into the formula 1, the assigned code amount b _i for the i-th frame, it can be determined by the following equation 4.

[0068]

(Equation 10)

Thus, the bit rate operation circuit 32
For example, the frame of the picture is complex image by increasing the assigned code amount b _i, for the simple picture frame to reverse to reduce the allocated code quantity b _i.

On the other hand, the inverse quantization circuit 18 includes the quantization circuit 1
The quantization data supplied from 6 is inversely quantized with the quantization step size set to 1, and coefficient data (to which quantization distortion is added) corresponding to the output of the DCT circuit 15 is reproduced. It is supplied to the IDCT circuit 20.

The IDCT circuit 20 converts the coefficient data into IDC
T-transform and reproduce input image data corresponding to the output of the predictive coding circuit 14 in the intra-frame coding mode, and reproduce difference data in the forward / backward / bidirectional prediction mode.
It is supplied to the addition circuit 21.

In the forward / backward / bidirectional prediction mode, the addition circuit 21 is supplied with the predicted image data which has been motion-compensated from the motion compensation circuit 23, and the difference between this predicted image data and the IDCT circuit 20. By adding the data, the image data corresponding to the input image data is reproduced.

The image data reproduced in this way is stored in the frame memory 22 as predicted image data. That is, the inverse quantization circuit 18 to the addition circuit 21
Constitutes a local decoding circuit, based on the prediction mode,
The quantized data output from the quantization circuit 16 is locally decoded, and the obtained decoded image is written to the frame memory 22 as a forward predicted image or a backward predicted image. The frame memory 22 is composed of a plurality of frame memories, a bank switching of the frame memories is performed, and, for example, a single frame is output as forward predicted image data or backward predicted image data according to an image to be encoded. Is output. In the case of forward / backward / bidirectional prediction, forward predicted image data and backward predicted image data are averaged and output, for example. These prediction image data are exactly the same image data as the image data reproduced by the image decoding device described later, and the next processed image is subjected to forward / backward / bidirectional prediction coding based on this prediction image. Will be

Next, the operation of the second encoding circuit 40 will be described. The circuits other than the quantization scale setting circuit 33, the delay unit 43, the quantization circuit 46, and the transmission buffer memory 49 constituting the second encoding circuit 40 are the circuits constituting the first encoding circuit 10 described above. Since the same operation as described above is performed, the description is omitted.

The delay unit 43 delays the input image data until, for example, an encoding control signal is output from the encoding control circuit 30. Then, the predictive encoding circuit 44, DC
In the T circuit 45, the delayed input image data is subjected to a predictive encoding process and a DCT transform process according to the prediction mode supplied from the intra-frame / forward / backward / bidirectional prediction determination circuit 13 to generate coefficient data. You.

The quantization scale setting circuit 33 divides the allocated code amount for each macroblock (for example, by dividing the allocated code amount for each frame by the number of macroblocks in one frame) from the supplied allocated code amount for each frame. Then, a comparison is made between the generated code amount generated in the macroblock detected from the buffer feedback from the transmission buffer memory 49 and the allocated code amount for each macroblock. When the quantization bit rate setting circuit 33 approaches the coding bit rate of each frame and the average coding bit rate for each set frame time, if the generated code quantity in the macro block is larger than the assigned code quantity for each macro block, If the quantization step size of the next macroblock is set large to suppress the generated code amount of the next macroblock, and if the generated code amount of the macroblock is smaller than the allocated code amount of each macroblock, the generated code amount , The quantization step size of the next macroblock is reduced. However, when the buffer feedback from the transmission buffer memory 49 indicates that the overflow of the transmission buffer memory 49 is close, the quantization scale setting circuit 33 does not depend on the above-described comparison result between the allocated code amount and the generated code amount. When the quantization step size is increased to suppress the overflow, and when the buffer feedback from the transmission buffer memory 49 indicates that the underflow of the transmission buffer memory 49 is near, the above-mentioned allocated code amount and generated code amount Regardless of the comparison result, the underflow is suppressed by reducing the quantization step size. In the above description, the generated code amount and the allocated code amount are compared for each macroblock, and the quantization step size is switched for each macroblock. However, the switching may be performed for each slice. In the above description, the generated code amount is detected from the amount stored in the transmission buffer memory 49.
Can also be obtained directly from the output of The quantization scale setting circuit 33 supplies the quantization step size thus set to the quantization circuit 46.

The quantization circuit 46 quantizes the coefficient data supplied from the DCT circuit 45 according to the quantization step size supplied from the above-described quantization scale setting circuit 33 to generate quantized data.

The VLC circuit 47 includes a quantization circuit 4
6, the quantization step size from the quantization scale setting circuit 33, the prediction mode from the intra / forward / backward / bidirectional prediction determination circuit 13,
Variable-length coding is performed together with the motion vector and the like from the motion vector detection circuit 11, and the obtained variable-length code data is supplied to the transmission buffer memory 49 as a second bit stream.

That is, in this image encoding apparatus, as shown in FIG. 3, for example, when image data is input via the delay unit 43 in step ST1, the process proceeds to step ST1.
In step 2, the quantization scale setting circuit 33 reads, from the encoding control circuit 30, the code amount allocated to the frame currently being encoded, and proceeds to step ST3.

In step ST3, the predictive coding circuit 44 to the VLC circuit 47 perform a predictive coding process and a DCT transform process on the image data, and quantize the coefficient data by a quantization step size based on the allocated code amount. Thereafter, variable-length coding is performed, and the process proceeds to step ST4.

In step ST4, for example, it is determined whether or not the encoding process has been completed for all frames (sequences) to which the same screen size and the same transfer rate are applied. Returns to step ST1. In this way, variable rate coding in which the coding rate is changed in frame units is realized, and even if images (frames) having complicated patterns continue, the quantization step size for these images is increased as in the conventional device. Without this, uniform high image quality can be obtained throughout.

Then, the transmission buffer memory 49 temporarily stores the variable-length code data, reads it out at a constant bit rate, and smoothes the variable-length code data to output it as a bit stream. The bit stream output from the transmission buffer memory 49 is multiplexed with, for example, an encoded audio signal, a synchronization signal, and the like, further added with an error correction code, and subjected to predetermined modulation suitable for transmission or recording. After being added, it is transmitted to an image decoding device via a transmission path, for example, or
As shown in (1), it is recorded on an image recording medium 55 composed of an optical disk, a magnetic disk, a magnetic tape or the like. That is,
In the second encoding circuit 40, for example in advance for the complex image by increasing the assigned code amount b _i, for the simple image subjected to variable rate encoding by reducing the allocated code quantity b _i Therefore, it is not necessary to apply a fixed rate of a high rate throughout in order to avoid extreme image quality deterioration for an image having a complicated pattern as in the conventional apparatus, and the recording time of the image recording medium 55 is increased. can do.

On the other hand, the inverse quantization circuit 48 includes the quantization circuit 4
6 is supplied to the above-described quantization circuit 4
6 is inversely quantized by the quantization step size used in
The coefficient data (to which the quantization distortion is added) corresponding to the output of the DCT circuit 45 is reproduced, and
It is supplied to the CT circuit 50. That is, the inverse quantization circuit 48 to the addition circuit 51 constituting the local decoding circuit locally decode the quantized data output from the quantization circuit 46 and use the obtained decoded image as a forward prediction image or a backward prediction image as a frame. Write to the memory 52. Frame memory 5
The image data stored in 2 is used as a predicted image for the next processed image.

By the way, in the above-described embodiment, the allocated code amount per predetermined time, that is, the average coding rate per predetermined time is obtained for each frame by using the frame as the predetermined time, but the present invention is not limited to this. It is not something to be done. For example, a so-called MPEG (Moving Picture Expert)
A GOP (Group of Picture) in a Group) may be set as a predetermined time. The above-mentioned MPEG is a so-called ISO.
(International Organization for Standardization) and IEC (International Electrotechnical Commission) J
SC (S) at TC (Joint Technical Committee) 1
ub Committee) 29 is a common name for a moving picture coding method under consideration in a WG (Working Group) 11.

That is, a GOP in MPEG is composed of at least one so-called I picture and a plurality of P pictures or B pictures (non-I pictures). Specifically, for example, as shown in FIG. 4, one I picture, four P pictures in a three-picture cycle, and ten B pictures
If the encoding control circuit 3
0 calculates the assigned code amount for each GOP. Here, an I picture is an image that is coded in a field or an intra-frame, and a P picture is an image that can be predicted only from the forward direction and is coded between a field or an inter-frame. Is an image that can be predicted from the forward direction, from the backward direction, and from both directions, and is encoded between fields or between frames.

Then, in the first encoding circuit 10,
For example, as shown in FIG. 5, any two consecutive pictures in the GOP are assumed to be I pictures and P pictures with the number of pictures constituting the GOP as a cycle, and the quantization step size is set to 1, for example. Predictive coding processing for image data of I picture and P picture, DCT
A conversion process and a variable-length coding process are performed to generate variable-length code data, and the variable-length code data is
Supply 0. Here, two pictures are I pictures,
The P picture is used to check the complexity of the picture and the correlation between the frames. The complexity of the picture can be known from the generated code amount of the I picture, and the We can know the correlation. In general, since a plurality of continuous frames have similar images, the tendency of the picture of the GOP can be seen even from the two extracted pictures.

[0087] The coding control circuit 30 is configured to count the data amount BITP _j data amount Biti _j and P picture of the I picture in each GOP, for example, as shown in the following formula 5, these data amount Biti _j, BITP _{Based on j} and the number N of P pictures constituting the GOP, a difficulty level (generated code amount) GOPd _j (j = 0, 1, 2,...) is obtained for each GOP.

[0088] Then _{GOPd j = bitI j + N ×} bitP j ··· Equation 5, the encoding control circuit 30, and the GOP for each of difficulty (amount of generated code) GOPd _j, based on the available data amount, The allocated code amount allocated to each GOP is obtained, and the allocated code amount is supplied to the second encoding circuit 40.

More specifically, the total number of GOPs is M, the total amount of usable data is B, the code amount allocated to the j-th GOP is GOPb _j , and the allocated code amount GOPb _j is expressed by the following equation (6). The total data amount B is obtained by adding the allocated code amounts GOPb _j of all the GOPs as shown in the following Expression 7. Note that a
Is a constant.

[0090]

[Equation 11]

Accordingly, the constant a can be obtained by the following equation 8, and when this constant a is substituted into the equation 6, the allocated code amount GOPb _j for the j-th GOP can be obtained by the following equation 9.

[0092]

(Equation 12)

Thus, the coding control circuit 30 increases the allocated code amount GOPb _j for a GOP containing a picture with a complicated pattern or a GOP having a low correlation between frames, for example. For a GOP that is included or has a high correlation between frames, the allocated code amount GOPb _j
Less.

Next, as shown in FIG. 6, for example, as shown in FIG.
When the image data is input through the step ST2, in step ST2, it is determined whether the currently input image data is the first picture of the GOP. If the image data is applicable, the process proceeds to step ST3, and if not, the process proceeds to step ST4.

In step ST3, the second encoding circuit 40 reads from the encoding control circuit 30 the amount of code allocated to the GOP currently being encoded, and proceeds to step ST4.

In step ST4, the second encoding circuit 40 performs a predictive encoding process and a DCT transform process on the image data, and quantizes the coefficient data with a quantization step size based on the allocated code amount. Variable length coding is performed, and the process proceeds to step ST5.

Here, the quantization scale setting circuit 33
From the supplied allocated code amount for each GOP, the allocated code amount for each frame is determined by the picture type (I
Picture, P picture, B picture), that is, the picture type shown in FIG. Specifically, the allocated code amount for the I picture is increased, the allocated code amount for the B picture is reduced, and the allocated code amount for the P picture is set in the middle. Subsequent processing of the quantization scale setting circuit 33 is the same as that of the embodiment in which the allocated code amount is obtained for each frame described above.

Next, in step ST5, it is determined whether or not the encoding process has been completed for all frames (sequences) to which the same screen size and the same transfer rate are applied. If it is, the process returns to step ST1. In this way, variable rate coding in which the coding rate is changed in GOP units is realized, and even if images (frames) having complicated patterns continue, the quantization step size for these images is increased as in the conventional apparatus. Without this, uniform high image quality can be obtained throughout. Further, in this embodiment, since the allocated code amount for each GOP is obtained based on two pictures, high-speed processing is possible as compared with the above-described embodiment. It is needless to say that the allocated code amount of each GOP may be obtained based on the data amount of all pictures in the GOP.

Note that the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, DCT is used for transform coding, but so-called strat transform, Haar transform, wavelet transform, etc. Is also good.

[0100]

As is apparent from the above description, according to the present invention, an input video signal is encoded, for example, predictive encoding, DCT
Transformation, quantization at a fixed quantization step size, and variable-length encoding to generate first encoded data, and the first encoded data at a predetermined time interval, for example, a data amount for each frame or each GOP. Based on the difficulty of encoding for each frame or GOP, and the sum of the difficulty of encoding a plurality of frames or GOPs, the difficulty of encoding for each frame or GOP and a plurality of frames or a plurality of Based on the ratio of the total sum of the degrees of difficulty of GOP encoding, an assigned code amount for each frame or GOP is obtained, and based on the assigned code amount, the input video signal is encoded at predetermined time intervals to perform second encoding. By generating data, variable-rate encoding in which the encoding rate changes at predetermined time intervals is realized, and even if images (frames) having complicated patterns are continuous, the quantization step size is dependent on these images. Without large is the fact as the device, it is possible to obtain a uniform image quality throughout.

Since the second encoded data obtained as described above has a variable rate, by recording this on an image recording medium, a limited recording capacity can be used effectively, and The recording time of the recording medium can be lengthened. Then, uniform high-quality image data can be reproduced from the image recording medium throughout.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a circuit configuration of a main part of an image encoding device to which the present invention has been applied.

FIG. 2 is a flowchart illustrating an operation of a first encoding circuit included in the image encoding device.

FIG. 3 is a flowchart illustrating an operation of a second encoding circuit included in the image encoding device.

FIG. 4 is a diagram showing each picture for explaining the structure of a GOP in MPEG.

FIG. 5 is a diagram illustrating each picture for describing an encoding control signal for each GOP.

FIG. 6 is a flowchart for explaining an operation of a second encoding circuit forming the image encoding device.

FIG. 7 is a diagram showing an image for explaining the principle of predictive coding.

FIG. 8 is a diagram showing an image for explaining the principle of motion compensated prediction coding.

FIG. 9 is a block diagram illustrating a configuration of an image encoding device and an image decoding device.

FIG. 10 is a diagram illustrating a configuration of a macroblock and a slice.

FIG. 11 is a block diagram showing a circuit configuration of a conventional encoder.

FIG. 12 is a block diagram showing a circuit configuration of a conventional decoder.

[Explanation of symbols]

10 first encoding circuit, 11 motion vector detection circuit, 12 frame memory group, 13 intra / forward / backward / bidirectional prediction determination circuit, 14 prediction encoding circuit,
15 DCT circuit 15, 16 Quantization circuit, 17 VL
C circuit, 18 inverse quantization circuit, 20 IDCT circuit, 2
1 addition circuit, 22 frame memory, 23 motion compensation circuit, 30 encoding control circuit, 31 counter, 32 bit rate operation circuit, 33 quantization scale setting circuit,
40 second encoding circuit, 43 delay unit, 44 predictive encoding circuit, 45 DCT circuit, 46 quantization circuit, 47
VLC circuit, 48 inverse quantization circuit, 49 transmission buffer memory, 50 IDCT circuit, 51 addition circuit, 52
Frame memory, 53 Motion compensation circuit, 55 Image recording medium

Claims (50)

(57) [Claims] 1. An image encoding method for encoding input image data, wherein the input image data is encoded for each GOP including a plurality of images to generate first encoded data for each GOP. Based on the data amount of the first encoded data generated in the step of generating the first encoded data,
Calculating the sum of the difficulty level of the encoding for each P and the difficulty level of the encoding of the plurality of GOPs, according to a ratio of the difficulty level of the encoding level of the GOP to the sum of the difficulty levels of the encoding of the plurality of GOPs. The amount of code to be allocated to each GOP itself is determined by the GOP including an image with a complicated pattern
And calculating the input image data for each GOP by assigning a larger amount of code to the GOP including a simple image. And the second
Generating the coded data of (1) and (2) so that the data amount of the second coded data for each GOP becomes the allocated code amount for each GOP. 2. The allocated code amount assigned to each GOP is obtained by multiplying the total amount of usable data by the ratio of the degree of difficulty of encoding for each GOP to the sum of the degree of difficulty of encoding the plurality of GOPs. 2. The image encoding method according to claim 1, wherein the image encoding method is obtained by: 3. The image encoding method according to claim 2, wherein the allocated code amount allocated to each GOP is obtained by the following equation. (Equation 1) Here, M is the number of the GOP, and j is 1 to M−
GOPdj is the assigned code amount for the j-th GOP, B is the total amount of usable data for the plurality of GOPs determined by the bit rate of the transmission path, and GOPdj is the j-th GOP Is the difficulty of encoding. 4. The method according to claim 1, wherein the difficulty of encoding for each GOP is obtained from a combination of a data amount of the first encoded data and a picture type of each image of each GOP. 4. The image encoding method according to any one of 3. 5. The step of obtaining the degree of difficulty of encoding for each GOP from a combination of the data amount of the first encoded data and a picture type includes: a data amount of an intra-coded image; Calculating the data amount of the inter-coded image for each GOP; obtaining the number of the intra-coded images and the number of the forward predicted inter-coded images for each GOP; The degree of difficulty of encoding for each GOP is calculated based on the data amounts of the intra-coded image and the forward predicted inter-coded image, and the intra-coded image and the forward predicted inter-coded image. The image encoding method according to claim 4, wherein the calculation is performed based on a combination with the number of images. 6. The image code according to claim 5, wherein the step of calculating the encoding difficulty level for each GOP calculates the encoding difficulty level for each GOP based on the following equation. Method. GOPdj = bitIj + N × bitPj Here, GOPdj is the difficulty of coding the j-th GOP, bitIj is the number of images to be intra-coded in the j-th GOP, and N is the intra-picture code. Is the number of images to be converted, and bitPj is the data amount of the image to be intra-coded in the j-th GOP. 7. The input image data for each GOP is converted to a GOP.
Generating the second encoded data by encoding based on the assigned code amount for each GOP; setting a quantization step size based on the calculated assigned code amount for each GOP; The method according to claim 1, wherein the input image data is encoded using a quantization step size to generate second encoded data according to the allocated code amount.
The image encoding method according to any one of claims 1 to 6. 8. An image encoding apparatus for encoding input image data, wherein a plurality of input image data of a GOP composed of a plurality of images are quantized using a fixed quantization step size.
First encoding means for generating first encoded data; and difficulty of encoding for each GOP based on a data amount of the first encoded data generated by the first encoding means. And the sum of the encoding difficulty of the plurality of GOPs is detected, and the allocated code amount assigned to each GOP itself according to the ratio of the encoding difficulty of the GOP to the sum of the encoding difficulty of the plurality of GOPs. Is assigned to a GOP including an image having a complicated pattern, and a GOP including an image having a simple pattern.
Encoding control means for calculating so as to be less allocated to the OP; and encoding the input image data for each GOP based on the allocated code amount allocated to the GOP itself.
And a second encoding unit that generates the encoded data of (1) and makes the data amount of the second encoded data of each GOP equal to the allocated code amount of each GOP. 9. The encoding control means according to claim 1, wherein the amount of code allocated to each of the GOPs is converted into a total amount of usable data, and a total of the difficulty of encoding the plurality of GOPs is calculated. 9. The image encoding apparatus according to claim 8, wherein the value is obtained by multiplying a difficulty ratio. 10. The encoding control means determines the difficulty of encoding for each GOP from a combination of the data amount of the first encoded data and the picture type of each image in each GOP. 10. The image encoding device according to claim 8, wherein 11. The encoding control means obtains, for each GOP, a data amount of an image to be intra-coded and a data amount of an image to be encoded between forward prediction images, The number of images to be coded and the number of images to be coded between the forward prediction images are obtained for each of the GOPs, and the difficulty of the coding for each GOP is determined between the intra coded image and the forward prediction image. 11. The image coding apparatus according to claim 10, wherein the calculation is performed based on a combination of a data amount of the image to be coded and the number of images to be coded between the intra-picture and the forward prediction picture. . 12. The encoding control means sets a quantization step size based on the calculated allocated code amount for each GOP, and the second encoding means sets the quantization step size by the encoding control means. 12. The image encoding apparatus according to claim 11, wherein the input image data is encoded using the determined quantization step size, and second encoded data is generated according to the allocated code amount. 13. The image encoding apparatus according to claim 12, wherein said encoding control means calculates the degree of difficulty of encoding for each GOP based on the following equation. GOPdj = bitIj + N × bitPj Here, GOPdj is the difficulty of coding the j-th GOP, bitIj is the number of images to be intra-coded in the j-th GOP, and N is the intra-picture code. Is the number of images to be converted, and bitPj is the data amount of the image to be intra-coded in the j-th GOP. 14. The encoding control means, wherein each of the GOPs
10. The image coding apparatus according to claim 9, wherein an amount of code to be allocated to is calculated by the following equation. (Equation 2) Here, M is the number of the GOP, and j is 1 to M−
GOPdj is the assigned code amount for the j-th GOP, B is the total amount of usable data for the plurality of GOPs determined by the bit rate of the transmission path, and GOPdj is the j-th GOP Is the difficulty of encoding. 15. An image encoding method for encoding input image data, comprising: encoding the input image data of a plurality of images to generate first encoded data for each image; Obtaining a sum of the difficulty of encoding for each image and the difficulty of a plurality of images based on a data amount of the first encoded data generated in the step of generating encoded data; The amount of code to be assigned to each image itself according to the ratio of the difficulty of encoding and the sum of the difficulty of encoding the plurality of images, a large amount is assigned to an image having a complicated pattern, and the pattern is simple. Calculating the input image data for each image based on the allocated code amount allocated to the image itself, and calculating the second encoded data. And making the data amount of the second encoded data for each image equal to the allocated code amount for each image. 16. The step of calculating an allocated code amount to be assigned to each image, comprising: calculating a total amount of data usable for a plurality of images within a predetermined time with respect to a total of the difficulty of encoding the plurality of images. 16. The image encoding method according to claim 15, wherein the distribution is proportionately performed based on a ratio of difficulty of each image. 17. The image coding method according to claim 16, wherein the code amount allocated to each image is obtained by the following equation. (Equation 3) Here, N is the number of the plurality of images, and i is 1 to
N is an integer of N-1, bi is the amount of code assigned to the i-th image, B is the total amount of data corresponding to the plurality of images, and di is the difficulty of encoding the i-th image. It is. 18. A method according to claim 18, further comprising the step of: encoding the input image data for each image from the assigned code amount of each image to obtain a quantization step size used when generating second encoded data. Claims 15 to 1
8. The image encoding method according to any one of items 7 to 7. 19. The quantization step size is set for each of macroblocks obtained by dividing each of the images into a plurality of pieces, and the quantization step size is such that the amount of code assigned to the macroblock is equal to that of the first encoded data. When the data amount of the corresponding macro block is smaller than the data amount of the corresponding macro block, the data amount of the second coded data is set to a larger value so as to decrease the data amount of the second coded data. 19. The image code according to claim 18, wherein when the data amount is larger than the data amount of the corresponding macroblock, the second coded data is set to a smaller value so as to increase the data amount. Method. 20. An image encoding apparatus that encodes input image data, wherein: a first encoding unit that encodes a plurality of the input image data to generate first encoded data; Based on the data amount of the first encoded data generated by the encoding means, the sum of the difficulty of encoding for each image and the difficulty of encoding for a plurality of images is obtained. The amount of code assigned to each image itself according to the ratio of the difficulty of the above and the sum of the difficulty of the encoding of the plurality of images, a large amount is assigned to an image having a complicated pattern, and an image is assigned to a simple image. Encoding control means for calculating so as to be allocated less, and encoding the input image data for each image based on the allocated code amount allocated to the image itself to generate second encoded data. And the above A second encoding unit that makes the data amount of the second encoded data equal to the allocated code amount for each image. 21. The encoding control means, comprising: a detection means for detecting a data amount of the first encoded data; and a data total amount usable for a plurality of images within a predetermined time, the plurality of images being 21. An arithmetic unit for calculating an allocated code amount allocated to each image by proportionally distributing the ratio of the difficulty level of each image to the total sum of the difficulty levels of encoding of the images. Image coding device. 22. The calculating means calculates the total amount of data as
22. The image encoding apparatus according to claim 21, wherein the image is assigned to each of the images according to the following equation. (Equation 4) Here, N is the number of the plurality of images, and i is 1 to
N is an integer of N-1, bi is the amount of code assigned to the i-th image, B is the total amount of data corresponding to the plurality of images, and di is the difficulty of encoding the i-th image. It is. 23. The encoding control means, which is connected to the arithmetic means and encodes the input image data for each image from the assigned code amount of each image to generate second encoded data. 23. The image encoding apparatus according to claim 20, further comprising a quantization scale setting unit that determines a quantization step size to be used. 24. The quantization scale setting means obtains the quantization step size for each of the macroblocks obtained by dividing each of the images into a plurality of pieces, and determines the quantization step size when the allocated code amount of the macroblock is The first
When the data amount of the corresponding coded data is smaller than the data amount of the corresponding macroblock, a larger value is set so that the data amount of the second coded data is smaller, and the allocated code amount of the macroblock is When the data amount is larger than the data amount of the corresponding macroblock of the first encoded data,
In order to increase the data amount of the second encoded data,
21. The image encoding apparatus according to claim 20, wherein the value is set to a smaller value. 25. An image encoding method for encoding input image data, wherein: selecting a prediction mode of each of a plurality of images represented by the input image data; and selecting the plurality of prediction modes according to the selected prediction mode. Encoding first input data for each pixel by encoding the input image data of the image, and the amount of the first encoded data generated in the step of generating the first encoded data Calculating the sum of the degree of difficulty of encoding for each image and the degree of difficulty of a plurality of images, based on the ratio of the degree of difficulty of encoding for each image and the sum of the degree of difficulty of the plurality of images. Calculating an assigned code amount to be assigned to each image itself, and dividing the input image data for each image by using the prediction mode and assigning an assigned code amount to each image itself. Encoding based on the code amount to generate second encoded data, so that the data amount of the second encoded data for each image becomes the allocated code amount for each image. Image coding method. 26. The method according to claim 26, further comprising: detecting a motion vector for each macroblock of the plurality of images; and encoding the input image data to generate first encoded data. Encoding the input image data using a vector, encoding the input image data to generate second encoded data,
26. The image encoding method according to claim 25, wherein the input image data is encoded using the prediction mode and the motion vector. 27. The step of calculating an assigned code amount assigned to each image, comprising: calculating a total amount of data usable for a plurality of images within a predetermined time with respect to a sum of the difficulty of encoding the plurality of images. 9. The method according to claim 8, wherein a proportional distribution is performed based on a difficulty ratio of each image, and the allocated code amount is allocated more to an image having a complicated pattern and less to an image having a simple pattern. 27. The image encoding method according to 25 or 26. 28. The image coding method according to claim 27, wherein the allocated code amount allocated to each image is obtained by the following equation. (Equation 5) Here, N is the number of the plurality of images, and i is 1 to
N is an integer of N-1, bi is the amount of code assigned to the i-th image, B is the total amount of data corresponding to the plurality of images, and di is the difficulty of encoding the i-th image. It is. 29. A method according to claim 29, further comprising the step of: coding the input image data for each image to determine a quantization step size used when generating second coded data from the allocated code amount of each image. Claims 25 to 2
9. The image encoding method according to claim 8. 30. The quantization step size is set for each of macroblocks obtained by dividing each of the images into a plurality of pieces, and the quantization step size is such that the amount of code assigned to the macroblock is equal to that of the first encoded data. When the data amount of the corresponding macro block is smaller than the data amount of the corresponding macro block, the data amount of the second coded data is set to a larger value so as to decrease the data amount of the second coded data. 30. The method according to claim 26, wherein when the data amount is larger than the data amount of the corresponding macroblock, the second encoded data is set to a smaller value so as to increase the data amount. Image coding method. 31. An image coding apparatus for coding input image data representing a plurality of images, comprising: a prediction determination unit for selecting a prediction mode of each of a plurality of images represented by the input image data; A first encoding unit that encodes the input image data of a plurality of images to generate first encoded data for each pixel according to the prediction mode, and a second encoding unit that generates the first encoded data for each pixel. The sum of the degree of difficulty of encoding for each image and the degree of difficulty of encoding a plurality of images is calculated based on the data amount of one encoded data, and the degree of difficulty of encoding for each image and the plurality of images are calculated. Encoding control means for calculating an assigned code amount assigned to each image itself based on the ratio of the total sum of the degree of difficulty of encoding, and input image data for each image, using the prediction mode, Every self Encoding is performed based on the allocated code amount to generate second coded data, and the data amount of the second coded data for each image is set to the allocated code amount for each image. An image encoding device comprising: a second encoding unit. 32. A motion vector detecting unit for detecting a motion vector for each macroblock of the plurality of images, wherein the first encoding unit uses the motion vector to
32. The image encoding apparatus according to claim 31, wherein the input image data is encoded, and wherein the second encoding unit encodes the input image data using the prediction mode and the motion vector. 33. The encoding control means, based on the sum of the degree of difficulty of encoding for each image and the degree of difficulty of encoding the plurality of images, assigns a large number to images with complicated patterns, 33. The image encoding apparatus according to claim 31, wherein the allocated code amount is calculated such that the amount of code allocated to a simple image is reduced. 34. The encoding control means, comprising: a detection means for detecting a data amount of the first encoded data; and a data total amount usable for a plurality of images within a predetermined time, the encoding control means comprising: 34. An arithmetic means for calculating an allocated code amount allocated to each image by proportionally distributing the ratio of the difficulty level of each image to the total sum of the difficulty levels of encoding. The image encoding device according to any one of claims 1 to 7. 35. The calculating means calculates the total amount of data as
The image encoding apparatus according to claim 31, wherein the image is assigned to each of the images according to the following equation. (Equation 6) Here, N is the number of the plurality of images, and i is 1 to
N is an integer of N-1, bi is the amount of code assigned to the i-th image, B is the total amount of data corresponding to the plurality of images, and di is the difficulty of encoding the i-th image. It is. 36. The encoding control means, which is connected to the arithmetic means and encodes the input image data for each image from the assigned code amount of each image to generate second encoded data. The image encoding apparatus according to any one of claims 31 to 35, further comprising a quantization scale setting unit that determines a quantization step size to be used. 37. The quantization scale setting means obtains the quantization step size for each of macroblocks obtained by dividing each of the images into a plurality of pieces, and determines the quantization step size when an amount of code allocated to the macroblock is determined. The first
When the data amount of the corresponding coded data is smaller than the data amount of the corresponding macroblock, a larger value is set so that the data amount of the second coded data is smaller, and the allocated code amount of the macroblock is When the data amount is larger than the data amount of the corresponding macroblock of the first encoded data,
In order to increase the data amount of the second encoded data,
37. The image encoding apparatus according to claim 32, wherein the value is set to a smaller value. 38. An image encoding method for encoding input image data, comprising: detecting a motion vector for each macroblock of a plurality of images represented by the input image data; Encoding input image data using the motion vector to generate first encoded data for each image; first encoded data generated in the step of generating the first encoded data Calculating the sum of the difficulty level of encoding for each image and the difficulty level of a plurality of images, based on the data amount of Calculating an assigned code amount to be assigned to each image itself based on the ratio; and dividing the input image data for each image by using the motion vector and for each image itself. Encoding is performed based on the allocated code amount to generate second coded data, and the data amount of the second coded data for each image is set to the allocated code amount for each image. And an image encoding method. 39. The step of calculating an allocated code amount to be assigned to each image, comprising: calculating a total amount of data usable for a plurality of images within a predetermined time with respect to a total sum of difficulty of encoding the plurality of images. 9. The method according to claim 8, wherein a proportional distribution is performed based on a difficulty ratio of each image, and the allocated code amount is allocated more to an image having a complicated pattern and less to an image having a simple pattern. 38. The image encoding method according to claim 38. 40. The image coding method according to claim 39, wherein the allocated code amount allocated to each image is obtained by the following equation. (Equation 7) Here, N is the number of the plurality of images, and i is 1 to
N is an integer of N-1, bi is the amount of code assigned to the i-th image, B is the total amount of data corresponding to the plurality of images, and di is the difficulty of encoding the i-th image. It is. 41. A method according to claim 41, further comprising the step of: encoding the input image data for each image, and calculating a quantization step size used when generating second encoded data, from the allocated code amount of each image. Claims 38 to 4
0. The image encoding method according to claim 1. 42. The quantization step size is set for each macroblock obtained by dividing each of the images into a plurality of pieces, and the quantization step size is such that the allocated code amount of the macroblock is equal to that of the first coded data. When the data amount of the corresponding macro block is smaller than the data amount of the corresponding macro block, the data amount of the second coded data is set to a larger value so as to decrease the data amount of the second coded data. 42. The image code according to claim 41, wherein when the data amount is larger than the data amount of the corresponding macroblock, the second coded data is set to a smaller value so as to increase the data amount. Method. 43. An image coding apparatus for coding input image data representing a plurality of images, wherein a motion vector is detected for each macroblock of the plurality of images represented by the input image data. Means, first image input means for encoding the input image data of the plurality of images using the motion vector, and first encoded data for each image, and first encoding means. On the basis of the data amount of the generated first encoded data, the sum of the encoding difficulty of each image and the encoding difficulty of a plurality of images is obtained, and the encoding difficulty of each image is calculated. Encoding control means for calculating an assigned code amount assigned to each image itself based on a ratio of a total sum of difficulty levels of encoding of the plurality of images, and using the motion vector as input image data for each image. When In addition, encoding is performed based on the assigned code amount assigned to each of the images themselves to generate second encoded data, and the data amount of the second encoded data for each image is An image encoding apparatus, comprising: a second encoding unit configured to set an assigned code amount. 44. The encoding control means, based on the sum of the difficulty of encoding for each of the images and the difficulty of encoding of the plurality of images, assigns a large number to an image having a complicated pattern. 44. The image coding apparatus according to claim 43, wherein the allocated code amount is calculated such that is less allocated to a simple image. 45. The encoding control means, comprising: a detecting means for detecting a data amount of the first encoded data; and a total data amount usable for a plurality of images within a predetermined time, the plurality of images being 44. An arithmetic unit for calculating an allocated code amount allocated to each image by proportionally distributing the ratio of the difficulty level of each image to the total sum of the difficulty levels of the encoding. The image encoding device according to claim 1. 46. The calculating means calculates the total amount of data as
The image encoding device according to claim 44, wherein the image is assigned to each of the images according to the following equation. (Equation 8) Here, N is the number of the plurality of images, and i is 1 to
N is an integer of N-1, bi is the amount of code assigned to the i-th image, B is the total amount of data corresponding to the plurality of images, and di is the difficulty of encoding the i-th image. It is. 47. The encoding control means, which is connected to the arithmetic means and encodes the input image data for each image from the assigned code amount of each image to generate second encoded data. The image encoding apparatus according to any one of claims 43 to 45, further comprising a quantization scale setting unit that determines a quantization step size to be used. 48. The quantization scale setting means obtains the quantization step size for each of macroblocks obtained by dividing each of the images into a plurality of pieces, and determines the quantization step size when an allocated code amount of the macroblock is determined. The first
When the data amount of the corresponding coded data is smaller than the data amount of the corresponding macroblock, a larger value is set so that the data amount of the second coded data is smaller, and the allocated code amount of the macroblock is When the data amount is larger than the data amount of the corresponding macroblock of the first encoded data,
In order to increase the data amount of the second encoded data,
48. The image encoding apparatus according to claim 47, wherein the value is set to a smaller value. 49. The method according to claim 1, wherein in the step of generating the first encoded data, encoding including a quantization process with a fixed quantization step size is performed.
39. The image encoding method according to 5, 25 or 38. 50. The image coding apparatus according to claim 8, wherein said first coding means performs coding including quantization processing at a fixed quantization step size. apparatus.