JPH07203448A - Dynamic image coding device and method therefor - Google Patents

Abstract

PURPOSE:To reduce the image quality deterioration due to fixed coding control. CONSTITUTION:A fixed coding block monitor circuit 74 monitors a fixed coding control signal from an image coding control circuit 82 to a fixed coding command circuit 70 and outputs a macro block position subject to fixed coding control in a preceding frame to a block coding correction control circuit 78. The circuit 78 outputs a correction control signal for coding control to a block subject to fixed coding in a preceding frame to the circuit 82. A fixed coding frame monitor circuit 76 informs it to a frame coding correction control circuit 80 when the preceding frame has a block subject to fixed coding control. The circuit 80 outputs a correction control signal for coding control to a succeeding frame to a frame having a block subject to fixed coding. The circuit 82 sets a high image quality coding parameter to a macro block subject to fixed coding processing in the preceding frame and sets a coding parameter to suppress a generated code quantity more than usual when the preceding frame has the fixed coding processing block.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving picture coding apparatus and method, and more particularly to a moving picture coding apparatus and method in a moving picture transmission apparatus.

[0002]

2. Description of the Related Art In recent years, the development of image compression coding technology and the widespread use of digital communication lines have been remarkable, and various communication protocols for videophones or videoconferences have been prepared as recommendations, and along with this, videophone devices and Various video and audio terminal devices such as a TV conference system have been proposed. As is well known, in order to directly digitally transmit moving image information, a transmission rate of several hundred Mbps is required. Therefore, various compression encoding methods for reducing the transmission rate and the transmission cost have been proposed. .

As compression coding methods for moving picture information in these moving picture communications, interframe coding for removing temporal redundancy by utilizing correlation in the temporal direction and orthogonal transform coding for utilizing correlation in the spatial direction. A hybrid coding method is often used, which is a combination of intra-frame coding that removes spatial redundancy by coding. Note that interframe coding includes motion-compensated interframe coding that compensates for motion between frames and interframe coding that does not perform motion compensation (simple interframe coding).

The motion-compensated interframe coding will be briefly described. When the object moves between frames, pixel data similar to the previous frame is present in the current frame at a position separated from the previous frame (reference frame) by the amount of movement of the object. Therefore, the motion vector of the object is estimated from the previous frame and the current frame, and the difference between the similar blocks is encoded. Of course, the motion vector is also encoded and transmitted together. This is the motion compensation interframe coding. Since the prediction error in motion-compensated interframe coding is smaller than the prediction error in simple interframe coding without motion compensation, it is possible to efficiently code an image with large motion.

As a motion vector detecting method, a block matching operation such as a sum of absolute differences between corresponding pixels is executed between a processing block of a current frame and a block pattern in a search area of a reference frame, A general method is to estimate a vector for a block in which the sum of absolute differences is a minimum as a motion vector.

For example, CCITT Recommendation H.264. In 261
For a macroblock of 16 pixels × 16 pixels, a motion vector search window of 48 pixels × 48 pixels is used, and the horizontal and vertical components of the motion vector are −15 to −15.
It is said that the detection is made with an integer of +15.

CCITT Recommendation H.264. According to H.261, there is an upper limit to the amount of generated code per frame after compression encoding. Therefore, the generated code amount must be controlled within these constraints, but since this control is usually feedback control, it may not be possible to follow a sudden and sudden increase in the code amount due to a scene change or the like.
In such a case, the coding control circuit forces the interframe coding mode (INTER mode) to be selected, and also causes the quantizing circuit to fix the quantized output to zero, thereby substantially reducing the code amount. 0, that is, the minimum. As a result, it becomes as if the inter-frame difference value is zero, and almost no significant data is generated, so that the code amount per frame can be set to the above upper limit or less. On the decoding side, the image data of the previous frame is effectively stored in the image memory as it is, and the image is displayed on the monitor.

There is a method called significant block determination.
Significant block determination is effective in increasing compression efficiency. That is, it is checked whether the inter-frame prediction error or the orthogonal transform coefficient value of the blocked image data satisfies a predetermined significant block determination criterion, and the block that does not satisfy the significant block determination criterion, that is, the insignificant block,
Similar to the fixed encoding process described above, the pixel value (difference value) in the invalid block or its transform coefficient is replaced with 0. Then, when it is determined that the block is the insignificant block, only the motion vector information of the block subjected to the motion compensation inter-frame coding mode processing is transmitted.

The significant / insignificant block determination condition has conventionally depended on whether or not there is a movement between blocks of preceding and following frames.

[0010]

In the conventional example, in the process of encoding image information in block units in a predetermined order,
The fixed coding control as described above is executed when the generated code amount exceeds a predetermined threshold value. The image of the block in which the fixed encoding control is executed is not substantially updated, so that a clear boundary is formed between the block in which the normal encoding is executed. Moreover, once the fixed coding process is started, the generated code amount can be quickly suppressed,
It is general that all the remaining blocks in the frame are fixedly encoded.

However, when the frame following the frame in which the fixedly coded block is present is interframe-coded, the image quality difference between the fixedly coded block position and the normally processed block position is obtained. May remain, and the visual discomfort resulting from this may continue for a long time.

Further, in the conventional example, fixed encoding control may be executed in consecutive encoded frames when scene changes are continuous or large movements of the entire screen are continuous. In such a case, the image of the block subjected to the fixed coding control is not updated at all, so that there is no continuity between the blocks that have been coded normally between consecutive frames, and the length is long. It produces multiple sharp boundaries over time, which results in image artifacts that can be visually annoying.

It is an object of the present invention to provide a moving picture coding apparatus and method for reducing the deterioration of image quality due to such fixed coding control.

Regarding the significant block determination, if the ratio of the insignificant blocks is increased, the generated code amount can be suppressed to be small, but the image quality of the received image is deteriorated. Generally, similarly to the control of the quantization characteristic, the image quality and the generated code amount, that is, the image quality and the motion followability can be controlled by controlling the significant block determination threshold.

In the conventional example, the significant block determination control by changing the significant block determination reference threshold value is configured to be adjusted based on the buffer accumulation amount or the user's image quality setting, as in the case of the quantization characteristic control. The code is assigned without distinguishing the background image and the person image in the frame. This is not efficient in allocating codes within the frame. Another object of the present invention is to provide a moving picture coding apparatus and method that solves such a problem.

[0016]

A moving picture coding apparatus according to a first invention is a moving picture coding apparatus which divides moving picture information into pixel blocks in a screen and codes the moving picture information. A predetermined value processing means for performing a process of setting the code amount of a predetermined pixel block to a predetermined value, a storage means for storing the pixel block processed by the predetermined value processing means, and a subsequent frame according to the storage information of the storage means. And a control means for controlling the amount of code assigned to each pixel block.

A moving picture coding apparatus according to a second aspect of the present invention is a moving picture coding apparatus for compressing and coding moving picture information in pixel block units by a motion-compensated interframe predictive coding method, and detecting a motion vector. And a significant block determining unit that determines whether each pixel block is an insignificant block using a determination criterion based on the output of the motion vector detecting unit.

A moving picture coding method according to a third aspect of the present invention is a moving picture coding method for compressing and coding moving picture information in pixel block units by a motion-compensated interframe predictive coding method, and detecting a motion vector. And a significant block determination step of determining whether each block is an insignificant block using a determination criterion based on the motion vector detected by the motion vector detection step.

A moving picture coding apparatus according to a fourth aspect of the present invention includes a difference calculation means for calculating a difference between moving picture information divided into pixel blocks in a screen and a prediction block of a preceding coded frame, and the difference. Orthogonal transforming means for orthogonally transforming the output of the computing means, quantizing means for quantizing the output of the orthogonal transforming means, variable length coding means for variable length coding the output of the quantizing means, and the variable length. And a smoothing buffer means for smoothing the output of the encoding means in accordance with the transmission speed of the transmission path, wherein the output of the quantizing means can be selectively fixed. Fixed coding control means for selectively controlling the fixed output of the, and fixed control block monitoring means for monitoring the block position where the fixed output of the quantizing means is selected by the fixed coding control means and storing it for a predetermined period, According to the monitoring result of the constant control block monitoring means, there is provided block coding correction control means for performing correction control so as to preferentially allocate a large code amount to a block for which a fixed output of the quantization means is selected at least in the immediately preceding frame. Is characterized by.

The moving picture coding apparatus according to the fifth aspect of the present invention includes a difference calculating means for calculating a difference between moving picture information divided into pixel blocks in a screen and a prediction block of a preceding coded frame, and the difference. Orthogonal transforming means for orthogonally transforming the output of the computing means, quantizing means for quantizing the output of the orthogonal transforming means, variable length coding means for variable length coding the output of the quantizing means, and the variable length. And a smoothing buffer means for smoothing the output of the encoding means in accordance with the transmission speed of the transmission path, wherein the output of the quantizing means can be selectively fixed. Fixed coding control means for selectively controlling the fixed output of the block, and a fixed control frame monitoring for monitoring the frame to which the block for which the fixed output of the quantizing means is selected by the fixed coding control means belongs and storing for a predetermined period. According to the monitoring result of the fixed control frame monitoring means, at least when there is a block in which the fixed output of the quantizing means is selected in the immediately preceding frame, continuous selection of the fixed output of the quantizing means is performed. Frame encoding correction control means for performing correction control so as to avoid it.

A moving picture coding method according to a sixth aspect of the present invention comprises a difference calculation step for calculating a difference between moving picture information divided into pixel blocks in a screen and a prediction block of a preceding coded frame, and the difference. Orthogonal transformation step for orthogonally transforming the output of the operation step, quantization step for quantizing the output of the orthogonal transformation step, variable length coding step for variable length coding the output of the quantization step, and variable length And a smoothing buffer step for smoothing the output of the encoding step according to the transmission speed of the transmission line, wherein the output of the quantizing means can be selectively fixed. According to the fixed control block monitoring step of monitoring the block position where the fixed output of is selected and storing for a predetermined period, and the monitoring result of the fixed control block monitoring step. Characterized in that it comprises a block coding correction control step of correcting control to preferentially allocate more code amount for a block that selects the fixed output of the quantization step in at least the immediately preceding frame.

A moving picture coding method according to a seventh aspect of the present invention comprises a difference calculation step for calculating a difference between moving picture information divided into pixel blocks in a screen and a prediction block of a preceding coded frame, and the difference calculation step. Orthogonal transformation step for orthogonally transforming the output of the operation step, quantization step for quantizing the output of the orthogonal transformation step, variable length coding step for variable length coding the output of the quantization step, and variable length And a smoothing buffer step for smoothing the output of the encoding step according to the transmission speed of the transmission path, wherein the output of the quantization step can be selectively fixed. A fixed control frame monitoring step of monitoring a frame to which a block whose fixed output is selected belongs and storing the frame for a predetermined period; and the fixed control frame monitoring step. According to the monitoring result, at least in the immediately preceding frame, when there is a block for which the fixed output of the quantization step is selected, the frame coding correction is controlled so as to avoid continuous selection of the fixed output of the quantization step. And a control step.

A moving picture coding method according to an eighth aspect of the invention is a moving picture coding method in which moving picture information is divided into pixel blocks in a screen and then coded. A predetermined value processing step for performing processing for setting the code amount to a predetermined value, a storage step for storing the pixel block processed by the predetermined value processing step, and allocation to each pixel block of the subsequent frame according to the storage information by the storage step And a control step for controlling the code amount.

[0024]

By the above means, the difference in image quality due to the difference in the encoding process in block units in the immediately preceding frame can be alleviated at an early stage. As a result, continuity can be realized between the blocks without any discomfort.

Further, in the frame next to the frame in which the fixed processing block exists, the generated code amount is controlled to be small. As a result, the probability that the immobilization process is executed in successive frames becomes low, and the image distortion due to the immobilization process can be significantly suppressed.

Depending on the magnitude of the motion vector in the processing block, if the motion is large, it is likely to be determined as an insignificant block, and if the motion is small, it is less likely to be determined as an inactive block. This makes it possible to realize adaptive significant block determination that considers visual characteristics for moving images.
The moving image information can be efficiently compressed and encoded.

[0027]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows a schematic block diagram of an embodiment of the present invention. This embodiment can be used as the image encoding circuit 22a of the image / audio communication device shown in FIG. 261 is configured.

First, FIG. 2 will be described. In FIG. 2, 1
0 is a camera for shooting conference participants, 12 is a document camera for shooting conference materials such as drawings, 14 is a camera 10, 12
Is an image input interface for selecting the output of the above and converting it into a predetermined internal format, 16 is a monitor for displaying an image, and 18 is an image output interface for supplying an image signal to the monitor 16.

The monitor 16 may be a single image display device or a plurality of image display devices, and further, a single image display device or a device capable of displaying a plurality of images in separate windows by a window display system. Good.

Reference numeral 20 is a selection / combination circuit that selects and combines the input images and the received images from the cameras 10 and 12 and supplies them to the image output interface 18, and 22 is an image encoding circuit 22a that encodes an image signal to be transmitted. The image coding / decoding circuit includes an image decoding circuit 22b for decoding the received coded image signal.

Reference numeral 24 is a handset consisting of a microphone and a speaker, 26 is a microphone, 28 is a speaker, and 30 is a voice input / output interface for the handset 24, the microphone 26 and the speaker 28. The voice input / output interface 30 not only switches the voice input / output of the handset 24, the microphone 26, and the speaker 28, but also performs echo / cancel processing, dial tone, ringing tone,
Tones such as busy tones and ring tones are generated. Reference numeral 32 is a voice encoding / decoding circuit including a voice encoding circuit 32a for encoding the voice signal to be transmitted and a voice decoding circuit 32b for decoding the received encoded voice signal.

34 is a communication line (for example, ISDN line)
Line interface 36 of the image coding circuit 22
a and the coded information to be transmitted from the voice coding circuit 32a are multiplexed and supplied to the line interface 34, and the coded image information and the coded voice information are separated from the received information supplied from the line interface 34, They are demultiplexing circuits which are supplied to the image decoding circuit 22b and the audio decoding circuit 32b, respectively.

Reference numeral 38 denotes the whole, particularly the image input interface 14, the image output interface 18, the selection / synthesis circuit 20, the image encoding / decoding circuit 22, the audio input / output interface 30, the audio encoding / decoding circuit 32, and the demultiplexing circuit 36. Reference numeral 39 is a system control circuit for controlling the system, and 39 is an operating device (for example, a ten-key or a keyboard) for the user to input a predetermined instruction to the system control circuit 38.

The flow of image signals and audio signals in FIG. 2 will be briefly described. The input images from the camera 10 and the document camera 12 are selected by the image input interface 14, and one of them is input to the selection / combination circuit 20. The selective synthesizing circuit 20 normally outputs the input images from the cameras 10 and 12 as they are to the encoding circuit 22a of the image encoding / decoding circuit 22. The image encoding circuit 22a encodes the input image signal in the encoding mode according to the control signal from the system control circuit 38 and the internal determination, and outputs it to the demultiplexing and multiplexing circuit 36, which will be described in detail later.

On the other hand, the input voice signal from the microphone or the microphone 26 of the handset 24 is input to the voice encoding circuit 32a of the voice encoding / decoding circuit 32 via the voice input / output interface 30 and is encoded and demultiplexed. 36
Applied to.

The demultiplexing / multiplexing circuit 36 includes the encoding circuit 22.
The coded signals from a and 32a are multiplexed and output to the line interface 34. The line interface 34 outputs the signal from the demultiplexing circuit 36 to the connected communication line.

The signal received from the communication line is supplied from the line interface 34 to the demultiplexing / multiplexing circuit 36. The demultiplexing circuit 36 separates the coded image signal and the coded audio signal from the received signal, and the image decoding circuit 22b respectively.
And to the audio decoding circuit 32b. The image decoding circuit 22 b decodes the coded image signal from the demultiplexing circuit 36 and applies it to the selective synthesizing circuit 20.

The selective combining circuit 20 is a system control circuit 38.
Image input interface 14 according to the control signal from
The input image from and the received image from the image decoding circuit 22b are selectively combined and output to the image output interface 18. The selective combining circuit 20 performs, for example, picture-in-picture or fitting into a corresponding window in the window display system as a combining process. The image monitor 16 displays the image signal from the image output interface 18 as an image. As a result, the input image and / or the received image is displayed on the screen of the monitor 16.

The received voice signal decoded by the voice encoding circuit 32b is applied to the speaker and / or the speaker 28 of the handset 24 via the voice input / output interface 30. As a result, the voice from the communication partner can be heard.

A command other than an image and a voice, which is transmitted to the communication partner, is directly supplied from the system control circuit 38 to the demultiplexing circuit 36, and the received command is sent from the demultiplexing circuit 36 to the system control circuit 38. Directly supplied to.

FIG. 1 will be described. 1 corresponds to the image encoding circuit 22a shown in FIG. In the encoding circuit shown in FIG. 1, an interframe encoding (INTER) mode in which a difference from the previous frame (predicted value) is encoded for each screen, and an intraframe code in which the difference is encoded within the screen without taking the difference Conversion (IN
The TRA) mode can be selected for each macroblock (details will be described later) in the frame. For example, the INTER mode is used for an image or a still image having little movement in the movement or time direction, and the INTRA mode is used for a scene change even for an image having a large movement or an image having little movement.
As described above, the INTER mode includes motion compensation and non-motion compensation. In addition, the quantization step size is changed according to the amount of encoded data to be generated, and if necessary, frame skipping (frame skip) is performed.

In FIG. 1, 40 is an input terminal for inputting pixel data from the selective synthesizing circuit 20, 42 is an energy comparison result between the pixel value from the input terminal 40 and a prediction error of the pixel value, and external control. It is an encoding mode selection circuit for selecting the INTRA mode or the INTER mode according to the signal. The encoding mode selection circuit 42 uses INTRA
In the mode, the pixel value from the input terminal 40 is output as it is, and in the INTER mode, the difference (prediction error) from the prediction value (previous frame) is output in macroblock units.

Reference numeral 44 denotes a D which outputs the DCT coefficient data by performing a discrete cosine transform on the output of the coding mode selection circuit 42.
The CT circuit, 46 is the DC output from the DCT circuit 44.
A quantizing circuit for quantizing the T coefficient data with a specified quantizing step size, 48 is a variable length coding circuit for variable length coding the output of the quantizing circuit 46, and 50 is a variable length coding circuit 48. Is an output terminal for connecting the output of the smoothing buffer 50 to the demultiplexing circuit 36.

Reference numeral 54 is an inverse quantization circuit for inversely quantizing the output of the quantization circuit 46, and reference numeral 56 is an inverse DCT circuit for inverse discrete cosine transform of the output of the inverse quantization circuit 54. 58 is I
In the NTER mode, the predicted value is added to the output of the inverse DCT circuit 56 and output, and in the INTRA mode, the inverse DCT circuit 56 is output.
It is an adder that outputs the output of as it is. 60 is a frame memory for motion-compensated inter-frame prediction,
The output (locally decoded value) of the adder 58 is stored.

Reference numeral 62 is a motion vector detection circuit for detecting a motion vector by comparing the image signal input from the input terminal 40 with the image signal of the previous frame stored in the frame memory 60 in macroblock units. According to the motion vector detected by the motion vector detection circuit 62,
A motion compensation circuit that moves the data of the previous frame from the frame memory 60 in a macro block unit within the screen to cancel the motion, and 66 is a low-pass filter that spatially filters the output of the motion compensation circuit 64 in the macro block unit. . The output of the filter 66 becomes a predicted value of inter-frame prediction, and is applied to the adder 58 and the subtractor 68. The subtractor 68 calculates the difference between the pixel data from the input terminal 40 and the output (predicted value) of the filter 66, that is, the prediction error, and supplies it to the coding mode selection circuit 42.

Reference numeral 70 denotes a fixed coding instruction circuit for instructing the coding mode selection circuit 42 to the interframe coding mode and for instructing the quantization circuit 46 to output zero.

A fixed coding block 74 monitors the fixed coding control by the fixed coding instruction circuit 70 and stores the macroblock position where the fixed coding control is executed at least until the coding process of the next frame is completed. Monitoring circuit, 7
A fixed-coded frame monitor 6 monitors fixed-encoding control by the fixed-encoding instruction circuit 70 and stores a frame including a macroblock for which fixed-encoding control is executed at least until the encoding process of the next frame is completed. Circuit, 78
Is a block coding correction control circuit that outputs coding correction control information in block units to the image coding unit control circuit 82 based on the fixed coding block position information from the fixed coding block monitoring circuit 74, and 80 is a fixed coding Based on the fixed encoded frame position information from the encoded frame monitoring circuit 76, the encoding correction control information for each frame is provided to the image encoding control circuit 82.
It is a frame coding correction control circuit for outputting to.

The image coding control circuit 82 normally operates
A control signal for encoding from the system control circuit 38,
Also, the coding mode selection circuit 42, the quantization circuit 46, the variable length coding circuit 48, and the fixed coding instruction circuit 70 are controlled according to the buffer accumulation amount signal from the smoothing buffer 50. The control signals related to encoding from the system control circuit 38 include a signal for designating image quality (spatial resolution) priority, motion followability (time resolution) priority, or an intermediate value thereof, a selection signal for the document camera 12, and the like. .

The operation of FIG. 1 will be described. For example, CCITT Recommendation H.264 is applied to the input terminal 40 from the selective combining circuit 20 (FIG. 1). CIF (Co
Image data is input in the Mmon Interface Format format or the QCIF (Quarter CIF) format. The structure of the CIF format is shown in FIGS. 4, 5, 6 and 7. In the CIF format, one frame of image data consists of 12 blocks called GOB (Group of Blocks), GOB consists of 33 blocks called macroblocks, and a macroblock consists of 6 blocks (4
One Y block, one Cb block and one Cr
Block), and the block is composed of 8 pixels × 8 lines.

The encoding process is performed in the order of GOBs # 1 to # 12 shown in FIG. 4 in the frame, in the order of macroblocks # 1 to # 33 shown in FIG. 5 in each GOB, and in each macroblock as shown in FIG. The Y blocks # 1 to # 4, the Cb block and the Cr block shown in FIG.

In the QCIF format, as shown in FIG. 8, each pixel and line in the CIF format is 1 /
It is set to 2.

In both formats, the coded transmission is G
OB units, motion compensation, quantization step size and coding mode selection are in macroblock units, and DCT and filter processing are in block units.

The image data input to the input terminal 40 is applied to the coding mode selection circuit 42, the subtractor 68 and the motion vector detection circuit 62.

The subtractor 68 calculates the difference (prediction error) between the pixel data from the input terminal 40 and the prediction value output from the filter 66, and applies it to the coding mode selection circuit 42. The coding mode selection circuit 42 performs energy comparison between the pixel value from the input terminal 40 and the prediction error from the subtractor 68, the comparison result, and the image coding control circuit 8
2 and the control signal from the fixed encoding instruction circuit 70,
Select the encoding mode. However, the coding mode selection circuit 42 selects the interframe coding mode according to the fixed coding mode control signal from the fixed coding instruction circuit 70. The circuit 42 outputs the input pixel value from the input terminal 40 to the DCT circuit 44 as it is when the INTRA mode is selected, and outputs the prediction error from the subtractor 68 to the DCT circuit 44 when the INTER mode is selected.

The DCT circuit 44 divides the data from the coding mode selection circuit 42 into discrete cosine (DC
T) transform and output the DCT coefficient data to the quantization circuit 46. The quantization circuit 46 quantizes the DCT coefficient data from the DCT circuit 44 with a quantization step size specified by the quantization characteristic control signal from the image coding control circuit 82. Although the details will be described later, the quantizing circuit 46 also becomes a zero output state in accordance with the fixed quantization control signal from the fixed encoding instruction circuit 70. Variable length coding circuit 48
Determines a significant block according to the coding control signal from the image coding control circuit 82, and sets the quantized DCT coefficient to CCIT.
Recommendation H.T. In accordance with H.261, variable length coding is performed.

The smoothing buffer 50 buffers the variable length coded data by the variable length coding circuit 48 and outputs it to the demultiplexing / multiplexing circuit 36 through the output terminal 52, and at the same time, controls the amount of buffer accumulation for image coding control. It is transmitted to the circuit 82. An error correction coding circuit may be connected between the smoothing buffer 50 and the output terminal 52.

The inverse quantization circuit 54 inversely quantizes the output of the quantization circuit 46 with the same quantization step size as that selected by the quantization circuit 46, and outputs the representative value of the DCT coefficient. The inverse DCT circuit 56 performs an inverse discrete cosine transform on the output of the inverse quantization circuit 54. The adder 58 adds the predicted value (output of the filter 66) to the output of the inverse DCT circuit 56 in the INTER mode, and inverse DCT in the INTRA mode.
The output of the circuit 56 is output as it is. The output of adder 58 is stored in frame memory 60.

The frame memory 60 has a storage capacity for at least two frames and stores the output pixel value (that is, the locally decoded value) of the adder 58. The motion vector detection circuit 62 compares the pixel data of the current frame from the input terminal 40 with the pixel data of the previous frame stored in the frame memory 60 to detect the motion of the image. Specifically, as shown in FIG. 9, the pixel data of the previous frame (reference frame) is set as a frame vector in the vicinity of a macroblock being processed in the current frame as a motion vector search window.
A motion vector is detected by reading from the memory 60 and performing block matching calculation.

The motion compensation circuit 64 moves the pixel data of the previous frame from the frame memory 60 in the screen direction so as to cancel the motion according to the motion vector detected by the motion vector detection circuit 62. The filter 66 performs filter processing on the pixel data of the previous frame that has been motion-compensated by the motion compensation circuit 64 to reduce discontinuity at the block boundary, and supplies the processed data to the subtractor 68 and the adder 58 as a predicted value. To do.

The image coding control circuit 82 responds to the control signal from the system control circuit 34 (such as the image quality control signal set by the user and the selection signal of the document camera 12) and the data storage amount of the smoothing buffer 50. Controls the overall image coding. Specifically, in order to prevent the smoothing buffer 50 from overflowing, the quantization is adaptively performed according to the change in the input image, the scene change, and the image quality setting of the communicator based on the data storage amount of the smoothing buffer 50. It controls the quantization step size of the circuit 46, the mode selection in the coding mode selection circuit 42, the significant block determination and the frame skip (frame skip).

Since the current frame and the previous frame are very similar to each other in an image with little movement or change, by using the INTER mode for encoding the difference from the previous frame,
The time redundancy can be reduced. By adding motion compensation, a moving image can be efficiently compressed. On the other hand, since the inter-frame correlation is small in the case of an image with a large motion or a scene change, the INTR encoded in the same frame
A mode is used.

Regarding the quantization characteristic, the quantization step
The smaller the size, the higher the image quality, but the more significant data, the more the number of transmission bits. On the other hand, if the quantization step size is increased, the amount of transmitted data decreases but the image quality deteriorates. CCITT Recommendation H.
According to H.261, there is an upper limit to the number of bits generated per frame, and there is also a limit to the improvement of quantization characteristics for high definition image quality. Higher image quality means an increase in the number of transmission bits, which leads to a reduction in the frame rate. That is, the image quality (spatial resolution) and the tracking ability (temporal resolution) of the movement are contradictory, and pursuing high image quality inevitably deteriorates the tracking ability of the motion. Therefore, the data storage amount of the smoothing buffer 50 is constantly monitored,
Quantize step size appropriately and efficiently. Also, the frame rate is adjusted by performing frame skip processing according to the number of encoded bits generated.

The circuits 74 to 82 which are the characteristic parts of this embodiment.
The correction control of the fixed encoding according to will be described in detail. The fixed coding block monitoring circuit 74 includes an image coding control circuit 82.
To the fixed encoding instruction circuit 70, the fixed encoding control signal is constantly monitored, and the position of the macroblock in which the fixed encoding control is executed is stored at least until the encoding process of the next frame is completed and the previous frame is stored. The macroblock position subjected to fixed coding control in (1) is output to the block coding correction control circuit 78. When the fixed coding block position information is input from the fixed coding block monitoring circuit 74, the block coding correction control circuit 78 outputs a correction control signal for coding control for a block fixedly coded in the previous frame to the image coding control circuit. To 82.

On the other hand, fixed coded frame monitoring circuit 76
Constantly monitors the fixed encoding control signal from the image encoding control circuit 82 to the fixed encoding control instruction circuit 70, similarly to the circuit 74, and of the frame in which the macroblock in which the fixed encoding control is executed exists. The position is stored at least until the encoding process of the next frame is completed, and the frame encoding correction control circuit 80 is notified that the fixed encoding control is performed in the previous frame. The frame coding correction control circuit 80 sends a correction control signal for coding control for the next frame of the fixed coded frame to the image coding control circuit 82 according to the fixed coded frame position information from the fixed coded frame monitoring circuit 76. Output to.

The image coding control circuit 82 corrects the coding control for each block according to the correction control signal from the block coding correction control circuit 78 as shown in FIG.
In accordance with the correction control signal from the frame coding correction control circuit 80, the coding control for each frame is corrected as shown in FIG.

FIG. 10 will be described. Image coding control circuit 8
2 monitors the generated code amount from the buffer accumulation amount information from the smoothing buffer 50 (S1), and when the buffer accumulation amount is a predetermined value or more (S2) or the code amount per frame is a predetermined value or more (S3), The coding mode is fixed to the interframe coding mode, and the quantized output is fixed to zero (S7). When the buffer storage amount is less than the predetermined value (S2) and the code amount per frame is less than the predetermined value (S3), the output of the block coding correction control circuit 78 indicates that the previous frame of the macroblock to be coded It is checked whether or not the fixed encoding process is performed (S4). If the fixed encoding process is not performed, a normal encoding parameter is selected (S5). If the fixed encoding process is performed, the image quality is high. An encoding parameter is selected (S6). Then, the target macroblock is encoded with the parameters set in S5, S6, and S7 (S8).

As described above, when the processing macroblock is subjected to fixed coding control in the immediately preceding frame, correction is performed so as to allocate a larger code amount, so that the peripheral area where normal coding is performed in the immediately preceding frame is performed. You can instantly reduce the difference in image quality from the macro block of.

FIG. 11 will be described. Image coding control circuit 8
2 checks from the output of the frame coding correction control circuit 80 whether or not there is a fixed coding processing block in the previous frame (S11), and if it does not exist, selects a coding parameter as usual (S12). If it exists, an encoding parameter that suppresses the code amount more than usual is selected (S13). The target frame is S
12, it is encoded with the encoding parameter selected in S13 (S14).

That is, when the fixed coding control is performed in the immediately preceding frame, the generated code amount of the next coded frame is suppressed. This prevents the fixed coding control from being continuously executed in consecutive frames.

In this embodiment, the amount of generated code after compression coding is efficiently suppressed in this way. Specifically, while preventing the overflow of the smoothing buffer and the increase in the code amount generated per frame due to a sudden increase in the code amount,
Distortion of an image and a difference in image quality due to no substantial image update are suppressed to a minimum.

Next, an embodiment of the present invention relating to significant block determination will be described. FIG. 12 shows a schematic block diagram of an embodiment which is supposed to be used as the image coding circuit 22a of FIG.

In FIG. 12, reference numeral 140 designates the selective synthesizing circuit 2.
0 is an input terminal for inputting CIF format or QCIF format pixel data, and 142 is an INTRA according to an energy comparison result between the pixel value from the input terminal 140 and a prediction error of the pixel value and an external control signal.
It is an encoding mode selection circuit for selecting a mode or an INTER mode. The encoding mode selection circuit 142 uses the INT
In RA mode, the pixel value from the input terminal 140 is output as it is, and in INTER mode, the difference (prediction error) from the prediction value (previous frame) is output in macroblock units.

Reference numeral 144 denotes a DCT circuit which performs discrete cosine transform on the output of the coding mode selection circuit 142 and outputs DCT coefficient data, and 146 designates the DCT coefficient data output from the DCT circuit 44 with a specified quantization step. -Quantization circuit for quantizing by size, 147 is the quantization circuit 14
6 is a significant block determination circuit that performs significant block determination, outputs the output of the quantization circuit 146 as is for significant blocks, and outputs zero for insignificant blocks, 1
Reference numeral 48 is a variable length coding circuit for variable length coding the output of the significant block determination circuit 147, 150 is a smoothing buffer for buffering the output of the variable length coding circuit 148, 1
52 is an output of the smoothing buffer 150 for the demultiplexing circuit 3
6 is an output terminal to be connected.

Reference numeral 154 is an inverse quantization circuit for inverse quantizing the output of the significant block determination circuit 147, and 156 is an inverse DCT circuit for inverse discrete cosine transform of the output of the inverse quantization circuit 154. 158 is an inverse DCT circuit 1 in the INTER mode
This is an adder that adds the predicted value to the output of 56 and outputs it, and in the INTRA mode, outputs the output of the inverse DCT circuit 156 as it is. A frame memory 160 for motion-compensated interframe prediction stores the output (locally decoded value) of the adder 158.

A motion vector detection circuit 162 detects a motion vector by comparing the image signal input from the input terminal 140 with the image signal of the previous frame stored in the frame memory 160 in macroblock units. In accordance with the motion vector detected by the motion vector detection circuit 162, a motion compensation circuit 166 that moves the data of the previous frame from the frame memory 160 within the screen in macro block units to cancel the motion, and 166 is a motion compensation circuit 164.
Is a low-pass filter that spatially filters the output of the macroblock. The output of the filter 166 becomes a predicted value of inter-frame prediction and is applied to the adder 158 and the subtractor 168. The subtractor 168 has an input terminal 140.
The difference between the pixel data from (1) and the output (predicted value) of the filter 166, that is, the prediction error is calculated and supplied to the coding mode selection circuit 142.

Reference numeral 170 is a determination threshold value control circuit for changing and setting the significant block determination circuit significant block determination reference threshold value in accordance with the motion vector detected by the motion vector detection circuit 162 and external threshold value control information.

Reference numeral 172 denotes the encoding mode selection circuit 1 according to the encoding control signal from the system control circuit 38 and the buffer accumulation amount signal from the smoothing buffer 150.
42, a quantization circuit 146, a variable length coding circuit 148, and a decision threshold value control circuit 170. The control signals related to encoding from the system control circuit 38 include a signal for designating image quality (spatial resolution) priority, motion followability (time resolution) priority, or an intermediate value thereof, a selection signal for the document camera 12, and the like. .

The processing flow of the image data in FIG. 12 will be described. The image data input to the input terminal 140 is applied to the coding mode selection circuit 142, the subtractor 168, and the motion vector detection circuit 162.

The subtractor 168 calculates the difference (prediction error) between the pixel data from the input terminal 140 and the prediction value output from the filter 166, and the coding mode selection circuit 14
2 is applied. The encoding mode selection circuit 142 performs energy comparison between the pixel value from the input terminal 140 and the prediction error from the subtractor 168, and selects the encoding mode according to the comparison result and the control signal from the image encoding control circuit 172. select. When the INTRA mode is selected, the circuit 142 directly inputs the input pixel value from the input terminal 140 to the DCT.
Output to the circuit 144, and when the INTER mode is selected,
The prediction error from the subtractor 168 is output to the DCT circuit 144.

The DCT circuit 144 performs a discrete cosine (DCT) transform on the data from the coding mode selection circuit 142 in block units, and the DCT coefficient data is quantized by the quantization circuit 14.
Output to 6. The quantization circuit 146 uses the quantization step size designated by the quantization characteristic control signal from the image coding control circuit 172 to generate the DC from the DCT circuit 144.
Quantize the T coefficient data. Significant block determination circuit 14
Reference numeral 7 designates a significant / insignificant block of the output of the quantization circuit 146 in block units according to the significant block determination threshold controlled and set by the determination threshold control circuit 170, and outputs the output of the quantization circuit 146 as it is for a significant block. However, zero is output for insignificant blocks. The variable length coding circuit 148 outputs the output of the significant block determination circuit 147 to CCITT Recommendation H.264. In accordance with H.261, variable length coding is performed.

The smoothing buffer 150 buffers the variable-length coded data from the variable-length coding circuit 148 and outputs the variable-length coded data to the demultiplexing / multiplexing circuit 36 through the output terminal 152, and the buffer accumulation amount is subjected to the image coding control. Circuit 172
Communicate to. An error correction coding circuit may be connected between the smoothing buffer 150 and the output terminal 152.

The inverse quantizer circuit 154 includes a quantizer circuit 146.
The output of the significant block determination circuit 147 is inversely quantized with the same quantization step size as that selected in, and the representative value of the DCT coefficient is output. The inverse DCT circuit 156 performs an inverse discrete cosine transform on the output of the inverse quantization circuit 154. In the INTER mode, the adder 158 uses the inverse DCT circuit 156.
The predicted value (output of the filter 166) is added to the output of
In the NTRA mode, the output of the inverse DCT circuit 156 is output as it is. The output of adder 158 is stored in frame memory 160.

The frame memory 160 has a storage capacity of, for example, 2 frames, and stores the output pixel value of the adder 158 (that is, the locally decoded value). The motion vector detection circuit 162 compares the pixel data of the current frame from the input terminal 140 with the pixel data of the previous frame stored in the frame memory 160, and detects the motion of the image. Specifically, as shown in FIG. 9, the pixel data of the previous frame (reference frame) is read from the frame memory 160 by using the vicinity of the macroblock being processed in the current frame as the motion vector search window, and the block matching calculation is performed. Then, the motion vector is detected.

The motion compensation circuit 164 moves the pixel data of the previous frame from the frame memory 160 in the screen direction according to the motion vector detected by the motion vector detection circuit 162 so as to cancel the motion. Filter 16
6 performs filter processing on the pixel data of the previous frame that has been motion-compensated by the motion compensation circuit 164 to reduce discontinuity at the block boundary, and supplies the processed data to the subtractor 168 and the adder 158 as a predicted value. .

The image encoding control circuit 172 responds to the control signals from the system control circuit 34 (such as the image quality control signal set by the user and the selection signal of the document camera 12) and the amount of data stored in the smoothing buffer 150. Controls the overall image coding. Specifically, in order to prevent the smoothing buffer 150 from overflowing, the quantization is adaptively performed according to the change in the input image, the scene change, and the image quality setting of the communicator based on the data storage amount of the smoothing buffer 150. Circuit 1
The quantization step size of 46, the mode selection in the coding mode selection circuit 142, the determination of the significant block determination threshold value in the determination threshold value control circuit 170, and the frame skipping (frame skip) are controlled.

The decision threshold control circuit 170 determines the threshold control signal from the image coding control circuit 172 based on the data storage amount of the smoothing buffer 150 and the image quality setting, and the decision target block output from the motion vector detection circuit 162. The significant block determination threshold in the significant block determination circuit 147 is controlled according to the motion vector. Basically, when the buffer storage amount is large, the ratio of insignificant blocks is increased to suppress the generated code amount. Conversely, when the buffer storage amount is small, the ratio of significant blocks is increased. Add image quality settings based on user preferences. Also, with respect to motion vectors, the fact that human visibility is low for moving objects makes it easy for a block with large motion to become an insignificant block depending on the absolute value of each motion vector. The significant block determination threshold is corrected as described above, and the significant block determination threshold is corrected so that a block having a small motion is unlikely to become an insignificant block.

A specific description will be given with reference to the flowchart shown in FIG. In this embodiment, the significant block judgment formulas are Σ | δi | ≦ aX and | δi | ≦ bY (for all i). Here, X and Y are determination reference values set in the same manner as in the conventional example, and a and b are correction coefficients for the determination reference values X and Y. Here, δi is a value obtained by taking the inter-frame difference for each pixel included in each block at the same position between the preceding and succeeding frames. A block that satisfies this condition is determined to be an insignificant block. The discrimination reference values X and Y are determined by the control information from the image coding control circuit 172, and the correction coefficients a and b are determined by the motion vector detected by the motion vector detection circuit 162. Note that δi does not have to be a block at the same position between preceding and succeeding frames, and may be a value obtained by taking an inter-frame difference for each pixel included in a block after motion compensation.

After determining the discrimination reference values X and Y based on the control information from the image coding control circuit 172 (S21), it is checked whether or not the absolute value of the detected motion vector is larger than the predetermined value K (S22). If it is larger than the predetermined value K, n and m are selected as the correction coefficients a and b (S23), and the predetermined value K
In the following cases, N and M are selected as the correction coefficients a and b (S24). However, N is smaller than n and M is smaller than m.

The judgment threshold values aX and bY thus determined by the judgment threshold value control circuit 170 are significant block judgment circuit 147.
The significant block determination circuit 147 applies the determination reference values X and Y determined in S21 and the correction coefficients a and b selected in S23 and S24 to the above equation to determine a significant / insignificant block (S25). ). As a result, a block whose motion vector is greater than the predetermined value K is likely to be an insignificant block, and conversely, a block whose motion vector is less than or equal to the predetermined value K is
It becomes difficult to become an unintentional block. As a result, in addition to the user's image quality setting and the amount of buffer storage, it is possible to realize efficient data allocation using the human visual characteristics.

In the above embodiment, only the significant block determination based on the quantized output of the orthogonal transform coefficient has been described, but it goes without saying that the significant block determination based on the inter-frame difference value is also applicable. In addition, CCITT Recommendation H.264. The present invention is not limited to the compression coding method according to H.261, and is directly applicable to many other coding methods.

Further, it may be combined with the conventional significant / insignificant block judgment reference control (for example, control based on the amount of data accumulated in the transmission buffer). It is also clear that some or all of the functions of this embodiment can be realized by software.

CCITT Recommendation H.264 Although the embodiment according to H.261 has been described, it is obvious that another encoding method, for example, an encoding method called MPEG method may be used.
It is also clear that some or all of the functions of this embodiment can be realized by software.

[0094]

As can be easily understood from the above description, according to the present invention, it is possible to quickly mitigate the image quality difference due to the difference in the encoding process in units of blocks of a predetermined size in the immediately preceding frame. Therefore, it is possible to achieve continuity between the blocks with little or no discomfort.

Further, since the amount of generated code is controlled to be small in the frame next to the frame in which the block in which the fixed encoding has been executed exists, the probability that fixed encoding will be executed in consecutive frames becomes low. As a result, it is possible to significantly suppress the image disturbance due to the fixed encoding process.

According to the magnitude of the motion vector of the processed block image, when the motion is large, it is easily determined to be an insignificant block, so that an adaptive significant block determination in consideration of visual characteristics can be performed on a moving image. This can be realized, and moving image information can be efficiently compressed and encoded.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention.

FIG. 2 is a basic configuration block diagram of an image communication device.

FIG. 3 is an operation flowchart of the embodiment shown in FIG.

FIG. 4 is an explanatory diagram of blocking of a CIF format, in which 12 GOBs (groups of
It shows the state divided into blocks.

FIG. 5 is a configuration diagram of GOB.

FIG. 6 is a configuration diagram of a macro block.

FIG. 7 is a block diagram of a minimum unit block.

FIG. 8 is an explanatory diagram of a QCIF format.

[Fig. 9] Fig. 9 is an explanatory diagram of a motion compensation interframe coding method.

10 is an operation flowchart of the embodiment shown in FIG.

FIG. 11 is an operation flowchart of the embodiment shown in FIG.

FIG. 12 is a schematic block diagram of a second embodiment of the present application.

[Explanation of symbols]

10: camera 12: document camera 14: image input interface 16: monitor 18: image output interface 20: selective combining circuit 22: image encoding / decoding circuit 22a: image encoding circuit 22b: image decoding circuit 24: handset 26: Microphone 28: Speaker 30: Voice input / output interface 32: Voice coding / decoding circuit 32a: Voice coding circuit 32b: Voice decoding circuit 34: Line interface 36: Demultiplexing / multiplexing circuit 38: System control circuit
39: Operating device 40: Input terminal 42: Encoding mode selection circuit 44:
DCT circuit 46: Quantization circuit 48: Variable length coding circuit 50: Smoothing buffer 52: Output terminal 54: Inverse quantization circuit 56: Inverse DCT circuit 58: Adder 6
0: Motion compensation frame memory 62: Motion vector detection circuit 64: Motion compensation circuit 66: Low-pass filter 68: Subtractor 70: Fixed encoding instruction circuit 7
4: fixed coding block monitoring circuit 76: fixed coding frame monitoring circuit 78: block coding correction control circuit
80: Frame coding correction control circuit 82: Image coding control circuit 140: Input terminal 142: Coding mode selection circuit 1
44: DCT circuit 146: Quantization circuit 147: Significant block determination circuit 148: Variable length coding circuit 150: Smoothing buffer 152: Output terminal 154:
Inverse quantization circuit 156: Inverse DCT circuit 158: Adder 160: Motion compensation frame memory 162: Motion vector detection circuit 164: Motion compensation circuit 166: Low pass filter 168: Subtractor 170: Judgment threshold control circuit 172:
Image coding control circuit

Claims (16)

[Claims] 1. A moving picture coding apparatus for coding moving picture information by dividing it into pixel blocks within a screen and coding the moving picture information by setting a code amount of a predetermined pixel block in the moving picture data to a predetermined value. Value processing means, storage means for storing the pixel block processed by the predetermined value processing means, and control means for controlling the code amount assigned to each pixel block of the subsequent frame according to the storage information of the storage means. And a moving picture coding device. 2. The control means preferentially increases the pixel block of the current frame corresponding to the processed pixel block when at least the pixel block processed by the predetermined value processing means exists in the immediately preceding frame. The moving picture coding apparatus according to claim 1, wherein the moving picture coding apparatus is controlled so as to allocate the code amount of. 3. A moving picture coding apparatus for compressing and coding moving picture information in pixel block units by a motion-compensated inter-frame predictive coding method, comprising motion vector detection means for detecting a motion vector, and the motion vector detection. And a significant block determining unit that determines whether each pixel block is an insignificant block by using a determination criterion based on the output of the unit. 4. The moving picture coding apparatus according to claim 3, wherein only a motion vector is coded for a block which is not judged to be significant by said significant block judgment means. 5. A moving picture coding method for compressing and coding moving picture information in pixel block units by a motion compensation interframe predictive coding method, comprising a motion vector detecting step of detecting a motion vector, and the motion vector detecting step. And a significant block determination step of determining whether each block is an insignificant block using a determination criterion based on the motion vector detected by the step. 6. The moving picture coding method according to claim 5, wherein only a motion vector is coded for a block which is not judged to be significant by said significant block judgment step. 7. A difference calculation means for calculating a difference between moving image information divided into pixel blocks within a screen and a prediction block of a preceding coded frame, and an orthogonal transformation means for orthogonally transforming an output of the difference calculation means. A quantizing means for quantizing the output of the orthogonal transforming means, a variable length coding means for variable length coding the output of the quantizing means, and a transmission rate of the output of the variable length coding means for a transmission line. And a smoothing buffer unit for smoothing the output of the quantizing unit, and a fixed coding control for selectively controlling the fixed output of the quantizing unit. Means, a fixed control block monitoring means for monitoring the block position in which the fixed output of the quantizing means is selected by the fixed encoding control means, and storing for a predetermined period, and a monitoring result of the fixed control block monitoring means. Accordingly, at least in the immediately preceding frame, there is provided block coding correction control means for performing correction control so as to preferentially allocate a large code amount to a block for which a fixed output of the quantization means is selected, and video coding. apparatus. 8. The moving picture coding apparatus according to claim 7, wherein said fixed coding control means selectively controls a fixed output of said quantizing means based on a data storage amount of said smoothing buffer means. 9. The fixed encoding control means selectively controls the fixed output of the quantizing means based on the amount of generated code per image frame in the output of the variable length encoding means. Or the moving picture coding device according to item 8. 10. A difference calculation means for calculating a difference between a moving image information segmented into pixel blocks in a screen and a prediction block of a preceding coded frame, and an orthogonal transformation means for orthogonally transforming an output of the difference calculation means. A quantizing means for quantizing the output of the orthogonal transforming means, a variable length coding means for variable length coding the output of the quantizing means, and a transmission rate of the output of the variable length coding means for a transmission line. And a smoothing buffer unit for smoothing the output of the quantizing unit, and a fixed coding control for selectively controlling the fixed output of the quantizing unit. Means, fixed control frame monitoring means for monitoring a frame to which a block whose fixed output of the quantizing means is selected by the fixed coding control means, and storing the frame for a predetermined period, and fixed control frame monitoring A frame for performing correction control so as to avoid continuous selection of the fixed output of the quantizing means at least when there is a block for which the fixed output of the quantizing means is selected in the immediately preceding frame according to the monitoring result of the means. A moving picture coding apparatus, comprising: a coding correction control means. 11. The moving picture coding apparatus according to claim 10, wherein said fixed coding control means selectively controls a fixed output of said quantization means based on a data storage amount of said smoothing buffer means. 12. The fixed coding control means selectively controls the fixed output of the quantizing means based on the amount of codes generated per image frame in the output of the variable length coding means. Or the moving picture coding device according to item 11. 13. Fixed control block monitoring means for monitoring the block position in which the fixed output of the quantizing means is selected by the fixed encoding control means, and storing the block for a predetermined period.
Block coding correction control means for performing correction control so as to preferentially allocate a large amount of code to a block for which a fixed output of the quantization means is selected in at least the immediately preceding frame according to the monitoring result of the fixed control block monitoring means. The moving picture coding device according to claim 10, 11 or 12. 14. A difference calculation step of calculating a difference between moving image information divided into pixel blocks in a screen and a prediction block of a preceding coded frame, and an orthogonal transformation step of orthogonally transforming an output of the difference calculation step. , A quantization step for quantizing the output of the orthogonal transformation step, a variable length coding step for variable length coding the output of the quantization step, and an output of the variable length coding step for the transmission rate of the transmission line. And a smoothing buffer step for smoothing the output of the quantizing means, which is capable of selectively fixing the output of the quantizing means. According to the fixed control block monitoring step of storing for a predetermined period and the monitoring result of the fixed control block monitoring step,
At least in the immediately preceding frame, a block coding correction control step for performing correction control so as to preferentially allocate a large code amount to a block for which a fixed output of the quantization step has been selected, the moving picture coding method. 15. A difference calculation step of calculating a difference between a moving image information divided into pixel blocks in a screen and a prediction block of a preceding coded frame, and an orthogonal transformation step of orthogonally transforming an output of the difference calculation step. , A quantization step for quantizing the output of the orthogonal transformation step, a variable length coding step for variable length coding the output of the quantization step, and an output of the variable length coding step for the transmission rate of the transmission line. And a smoothing buffer step for smoothing the output of the quantization step, which is a moving image coding method, in which the frame to which the block whose fixed output of the quantization step is selected belongs. According to the fixed control frame monitoring step of monitoring and storing for a predetermined period and the monitoring result of the fixed control frame monitoring step,
At least when there is a block for which fixed output of the quantization step is selected in the immediately preceding frame, a frame coding correction control step for controlling so as to avoid continuous selection of the fixed output of the quantization step. A moving image encoding method comprising: 16. A moving picture coding method for coding moving picture information by dividing it into pixel blocks within a screen and coding the moving picture information so that the code amount of a predetermined pixel block of the moving picture data has a predetermined value. A value processing step, a storage step of storing the pixel block processed by the predetermined value processing step, and a control step of controlling the code amount to be assigned to each pixel block of the subsequent frame according to the storage information of the storage step. And a moving picture coding method.