JPH09168154A - Dynamic image coding method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce transmission information quantity by selecting a motion vector with a minimum magnitude within a range where a coding object macro block is discriminated to be nonsignificant in the coding of a motion compensation prediction error method. SOLUTION: A frame memory 4 stores a video signal from an input section 2 and gives a video signal 5 of a coding object macro block of a current frame to a subtractor section 13 and gives a video signal 7 of each macro block of a preceding frame to a motion compensation section 8. The motion compensation section 8 gives a video signal 12 of a macro block of a preceding frame whose motion is compensated by motion vector information 9 to a subtractor section 13. A significance/non-significance discrimination section 15 discriminates an inter-macro block difference value 14 from the subtractor section 13 based on a threshold level to give a macro block significance signal 21 to a coding engine section. A motion vector generating section 11 generates motion vector information 9 whose picture element is increased by a prescribed number so as to increase the magnitude sequentially while being started from a zero vector (0,0).

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 method and apparatus for motion-compensating and coding a moving picture signal,
In particular, the present invention relates to a moving picture coding method and apparatus which are effective when transmitting at a low bit rate.

[0002]

2. Description of the Related Art In a conventional moving picture coding apparatus using a block matching method, a macroblock to be coded is classified into significant / insignificant and only significant blocks are coded to reduce the amount of information. Be seen.

That is, the difference between a current macroblock to be coded and a motion-compensated macroblock of the previous frame is calculated, and a macroblock whose difference value is below a certain threshold is treated as a non-significant macroblock. For stationary macroblocks that transmit only vectors and are insignificant and have zero motion vectors, no coding has been used.

[0004]

According to such a conventional method, the difference (distortion) between the current macroblock to be coded and the motion-compensated macroblock of the previous frame is minimized. Since the block matching method of detecting the motion vector according to the macroblock of the frame and performing the motion compensation by the detected motion vector is used, the following problems occur.

When the significance of the macroblock is determined as described above in the system in which the macroblock of the reference image is obtained so as to minimize the difference value (distortion) and the motion vector is detected, it is determined to be insignificant. There is a risk that a motion vector of an unnecessary size will be transmitted for the macroblock. In other words, in a non-significant macroblock, the information to be transmitted is only the motion vector, so that it is possible to perform motion compensation with sufficient accuracy even with a small motion vector, or when the difference value does not increase much without motion compensation. A large motion vector is also sent to, and useless information is transmitted accordingly.

Therefore, it is an object of the present invention to provide a moving picture coding method and apparatus capable of reducing the amount of transmitted information while preventing deterioration of image quality.

[0007]

According to the present invention, motion compensation is performed on a macroblock of a previous frame by using a generated motion vector, and a macroblock subjected to motion compensation and a macroblock to be coded of a current frame. By calculating the prediction error which is the difference and comparing the calculated prediction error with the threshold value, it is determined whether this macroblock to be coded is a non-significant macroblock smaller than the threshold value or a significant macroblock larger than the threshold value. The present invention relates to a moving picture coding method in which coding is performed when a block is a block, and only the above motion vector is transmitted when a block is a non-significant macroblock. Particularly, according to the present invention, the motion vector having the smallest size is selected within the range in which the macroblock to be encoded is determined to be insignificant.

Since the motion vector having the smallest size is selected within the range in which the macroblock to be coded is determined to be insignificant, the amount of motion vector information to be transmitted is small when only the motion vector is transmitted. Therefore, the amount of transmitted information can be reduced.

A motion vector is generated by sequentially increasing the motion vector from the smallest motion vector, and each time the motion vector is generated, motion compensation is performed using the generated motion vector, a prediction error is calculated, and the calculated prediction error is set as a threshold value. It is preferable to make a distinction between significant and insignificant by comparing with.

It is also preferable that the threshold value is determined by a function including the magnitude of the motion vector as a parameter. In this case, the function may be a function that decreases when the size of the motion vector increases, or a function that decreases when the size of the motion vector increases and saturates when the motion vector exceeds a certain value. preferable. As a result, the smaller the motion vector, the easier it is to determine as a non-significant macroblock.

The present invention further includes a motion vector generating means for generating a motion vector, a means for performing motion compensation on a macroblock of a previous frame using the generated motion vector, and a motion-compensated macroblock and a current block. Means for calculating a prediction error that is the difference between the frame and the macroblock to be coded, and comparing the calculated prediction error with a threshold, this macroblock to be coded is a non-significant macroblock that is smaller than the threshold or has a significant significance. A moving picture coding apparatus provided with a judging means for judging whether the macroblock is a macroblock, and coding means if the macroblock is a significant macroblock, and means for transmitting only the above motion vector if the macroblock is a non-significant macroblock. It is related to Particularly, in the present invention, the motion vector generating means is configured to select the motion vector of the smallest size within the range in which the macroblock to be encoded is determined to be insignificant.

Since the motion vector having the smallest size is selected within the range where the macroblock to be coded is determined to be insignificant, the amount of motion vector information to be transmitted is reduced when only the motion vector is transmitted. It is possible to reduce the amount of transmitted information.

The motion vector generating means is means for sequentially increasing the motion vector from the smallest motion vector and generating the motion vector. The motion compensating means, the calculating means and the discriminating means are generated each time the motion vector is generated. It is preferable that it is a means for performing a motion compensation using a motion vector, calculating a prediction error, and comparing the calculated prediction error with a threshold value to determine whether the error is significant or not.

It is also preferable that the discriminating means has a function for including the magnitude of the motion vector as a parameter to determine the threshold value. In this case, it is preferable that the function is a function that decreases when the magnitude of the motion vector increases, or a function that decreases when the magnitude of the motion vector increases and saturates when the motion vector exceeds a certain value. As a result, the smaller the motion vector, the easier it is to determine as a non-significant macroblock.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram schematically showing the configuration of an embodiment of a moving picture coding apparatus of the present invention.

In the figure, reference numeral 1 shows the configuration of the entire variable frame rate moving image coding apparatus. The moving picture coding apparatus 1 includes a video signal input unit 2, a frame skip unit 3 which is connected to the video signal input unit 2 and performs frame skip on the input video signal, and the frame skip unit 3. Connected to the frame memory 4 for storing at least the video signals of the previous frame and the current frame which are input after skipping the frame, and the current-frame coding target macroblock (the macroblock of interest) output from the frame memory 4. ) And the encoding engine unit 6 to which the video signal 5 of FIG.

The frame memory 4 is connected to the above-described encoding engine unit 6, motion compensation unit 8, and subtraction unit 13. As will be described later, the motion vector generation unit 11 that sequentially generates the motion vector from the smallest to the long scalar length and outputs the motion vector information 9 and the scalar length information 10 includes the motion compensation unit 8 and the encoding engine. Part 6
The VLC (variable length coding unit) 23, the macroblock significant / insignificant determination unit 15, and the frame skip number determination unit 20 are connected to each other. The motion compensation unit 8 outputs the video signal 7 of each macroblock of the previous frame to the frame memory 4
Given by

The subtractor 13 receives the video signal 5 of the macroblock of interest of the current frame from the frame memory 4 connected to its + input, and the motion compensated previous frame of the previous frame from the motion compensator 8 connected to its − input. The video signal 12 of the macro block is input. The output of the subtraction unit 13 is connected to the significance / insignificance determination unit 15. The significance / insignificance determination unit 15 includes a difference value 14 between macro blocks from the subtraction unit 13.
The scalar length information 10 is input from the motion vector generator 11. The output of the significant / insignificant determination unit 15 is connected to the frame skip number determination unit 20.

The frame skip number determination unit 20 is further connected to the output buffer memory unit 17 and the frame skip unit 3, and the significant / insignificant determination unit 15 outputs the significant macroblock ratio information 16 to the motion vector generation unit 1.
1 to the scalar length information 10 are respectively input from the output buffer memory unit 17 to the generated information amount 18 up to immediately before, and the frame skip number information 19 is generated and output to the frame skip unit 3 and the encoding engine unit 6.

The variable length coding unit 23 is connected to the significant / insignificant judgment unit 15, the coding engine unit 6 and the motion vector generation unit 11, and the macroblock significant information 21 and the quantization information are respectively connected thereto. 22 and motion vector information 9
Is received and encoded. The variable length coding unit 23 is further connected to the input of the output buffer memory unit 17 and outputs a coded output 24. The output of the output buffer memory unit 17 is connected to the code output unit 25.

The encoding engine unit 6 has a known encoding device configuration except for a part of the configuration described later. That is, the mode switches 6a and 6b for switching between inter-frame prediction and intra-frame prediction, the subtraction unit 6c, the addition unit 6d, the significant / insignificant determination unit 15 to the significant information according to the macroblock significant information 21. Switch 6e, which is turned on when it is insignificant, and turned off when it is insignificant, a DCT (discrete cosine transform) circuit 6f, a Q (quantization circuit) 6g, a Q ^-1 (inverse quantization circuit) 6h, and an IDCT ( It is mainly composed of a discrete cosine inverse transformation circuit 6i, a frame memory 6j, and a motion compensation section 6k.

FIG. 2 is a flow chart for explaining the main operation in this embodiment. The operation of this embodiment will be described below with reference to this drawing.

When the video signal is input to the video signal input section 2 (step S1), it is determined whether this frame is the first frame (step S2). If it is the first frame, the video signal is input to the frame memory unit 4 and stored in the current frame memory (Step S4) without performing the frame skip operation in the frame skip unit 3 (Step S3). Then, it is determined again whether this frame is the first frame (step S
5).

If the frame is the first frame, the frame skip number 19 output from the frame skip number determining unit 20 is set to an initial value N (sheet) (step S6).
Next, the video signal is input to the encoding engine unit 6 to be subjected to intra-frame encoding, converted into a bit stream by the variable length encoding unit 23, and then output buffer memory unit 1
The code is output from the code output unit 25 through step 7 (step S7). Then, the contents stored in the current frame memory of the frame memory unit 4 are moved to the previous frame memory (step S8), and the process returns to step S2.

Since the subsequent frames are the second and subsequent frames,
In the frame skip unit 3, the number of frame skips is 1
The frame skip operation of the input video signal according to 9 is performed (step S3). The frame skipped video signal in the frame skip unit 3 is stored in the frame memory 4
Is stored in the current frame memory (step S4). After that, the images stored in the current frame memory and the previous frame memory of the frame memory 4 are divided into a predetermined number of macroblocks (step S9).

Then, it is judged whether or not the processing has been completed for all macroblocks of the current frame (step S
10), if not completed, the motion vector generator 11
Then, a motion vector is generated (step S11).
This motion vector is generated by incrementing by a constant number of pixels such that its magnitude gradually increases from the zero vector (0, 0).

FIG. 3 is a conceptual diagram of the operation of the motion vector generating section. The motion vector generating section 1 will be described below with reference to the same figure.
1 will be described. Each grid in FIG. 3 indicates the minimum unit of motion vector. For example, if the increment step of the motion vector is 1/4 pixel unit, each grid is 1/4.
Represents a pixel. Circled numbers are the order in which motion vectors are generated. Starting from the zero vector (0,0), (0,1), (1,
0), (0, -1), (-1, 0), (1,
1), ..., And the motion vectors are generated in ascending order of magnitude.

This motion vector is the motion vector information 9
Is applied to the motion compensation unit 8, the encoding engine unit 6 and the variable length encoding unit 23. Further, the scalar length is applied as motion vector scalar length information 10 to the macroblock significance determination unit 15 and the frame skip number determination unit 20.

Next, the motion vector generation unit 11 determines whether or not all types of motion vectors have been generated (step S12). If not generated, the motion compensation unit 8 performs motion compensation processing for that macroblock. (Step S13). That is, a macroblock which is motion-compensated with respect to the macroblock of interest of the previous frame stored in the frame memory 4 is extracted by one motion vector information 9 provided from the motion vector generation unit 11,
It is output as the motion compensation macroblock 12.

Next, the target macroblock 5 and the motion compensation macroblock 12 of the current frame are input to the subtraction unit 13, the difference absolute value 14 (distortion) for each pixel is calculated, and the macroblock significance judgment unit 15 is calculated. Is output (step S1
4). The macroblock significance judgment unit 15 judges from the absolute difference value 14 whether the macroblock is significant or insignificant (step S15).

FIG. 4 is a conceptual diagram of the operation of the macroblock significance judgment unit 15, and the function of the significance judgment unit 15 will be described below with reference to the figure. First, the macroblock is divided into four vertically and horizontally half, and the sum of absolute differences between the divided blocks is calculated. The four sum values are T1, T
2, T3, T4, the maximum one of T1 to T4 max (T1, T2, T3, T4) is determined to be a significant macroblock if the macroblock exceeds the threshold Th, and a non-significant macroblock otherwise. To do.

The threshold value Th for this determination is determined by a function including the motion vector scalar length as a parameter, as an example is shown in FIG. This function is not limited to the characteristic curve shown in FIG. 5, and may be a characteristic that is large when the motion vector scalar length is small, decreases when the motion vector length becomes large, and saturated when the motion vector exceeds a certain value. Any characteristic curve (straight line) may be used.
As a result, the smaller the motion vector, the more likely it is to be determined as a non-significant macroblock.

If it is determined to be non-significant, the motion vector and its "non-significant" information are saved (step S16),
The process proceeds to the next macroblock (step S17) and the processes of steps S10 to S18 are repeated. If it is determined to be significant, the process returns to step S11 to generate a motion vector of the next magnitude, and the same processing in steps S12 to S15 is performed.

In step S12, when the motion vector generation unit 11 determines that all types of motion vectors have been generated, the macroblock has not been determined to be insignificant until the end, and is finally a significant macroblock. It will be. In this case, the motion vector having the smallest inter-frame difference value and its difference value are stored (step S18), and the process proceeds to the next macroblock (step S1).
7), the processes of steps S10 to S18 are repeated.

In this way, the significance of the current frame is determined for each of the vectors obtained from the motion vector generator 11 for each macroblock. When this process is completed for all macroblocks (step S
10), the number of skips 19 up to the next frame is calculated by the frame skip number determiner 20 (step S1).
9). The frame skip number determination unit 20 uses the ratio information 16 of significant macroblocks in the input frame,
Scalar length information of motion vector of significant macroblock 1
0 and / or the number of frame skips 19 by a function including the generated information amount 18 up to immediately before encoding as a parameter
To determine.

FIG. 6 shows an example of preferable characteristics of the number of frame skips with respect to the ratio of significant macroblocks. When the significant macroblock ratio is zero, the number of frame skips is zero, the number of frame skips increases as the significant macroblock ratio increases, and the characteristic becomes saturated when the significant macroblock ratio exceeds a certain value. The numerical value of the number of frame skips in the figure is merely an example and is not limited to this.
In this way, when the ratio of significant macroblocks that occupy the current frame is large, the amount of information required to encode that current frame is considered to be large, so the number of frame skips is required until a certain quality can be maintained. Is set to the minimum necessary. However, since a large increase in the number of frame skips reduces the efficiency of information amount reduction due to motion compensation, the number of frame skips 19 is saturated instead of continuing to increase with the increase in the significant macroblock ratio 16. Such a tendency.

FIG. 7 shows an example of preferable characteristics of the number of frame skips with respect to the scalar length of the motion vector. It has a characteristic that the number of frame skips decreases as the motion vector scalar length increases. The numerical value of the number of frame skips in the figure is merely an example and is not limited to this. As described above, when the motion vector scalar length 10 of the significant macroblock is large, increasing the frame skip number 19 results in an image in which the motion is visually unnatural.
9 is decreased a little.

FIG. 8 shows an example of preferable characteristics of the number of frame skips with respect to the amount of information generated up to immediately before (ratio of the information storage amount to the capacity of the output buffer memory unit 17). The characteristic is that the number of frame skips increases as the amount of generated information up to immediately before increases. The numerical value of the number of frame skips in the figure is merely an example and is not limited to this. In this way, when the generated information amount 18 up to immediately before is large, the number of skips is slightly increased to suppress the generated information amount to prevent buffer overflow.

The number of frame skips is one of the above-mentioned ratio of significant macroblocks, the motion vector scalar length of significant macroblocks, and the amount of generated information immediately before encoding.
It may be a function having two as parameters, or a function having all of these as parameters.

FIG. 9 three-dimensionally represents the preferable characteristic of the number of frame skips in that case. That is, when the significant macroblock ratio is zero, the number of frame skips is zero, and as the significant macroblock ratio increases, the number of frame skips also increases. When the significant macroblock ratio exceeds a certain value, it is saturated and the motion vector scalar The number of frame skips decreases as the length increases, and the number of frame skips increases as the amount of generated information up to immediately before increases.

As an example, the significant macroblock ratio in the target frame is 30%, and the motion vector scalar length is 6
0, assuming that the information generation amount up to immediately before occupies 70% of the output buffer, the skip number is 7 from FIG. 6, the skip number is +1 from FIG. 7, and the skip number is −1 from FIG. So the final number of frame skips is
7 + 1 + (-1) = 7 sheets.

After the number of frame skips up to the next frame is determined, the determined frame skip number 19, the target macroblock 5 of the current frame, the motion vector information 9, and the significant information 21 of the macroblock are respectively encoded. (Step S20), the motion vector information 9 and the macroblock significant information 21 are input to the variable length coding unit 23.

In the encoding engine unit 6, the determined frame skip number 19 is input to the quantizing unit 6g and used as a parameter for selecting a quantizer. When the number of frame skips 19 is large, a slightly fine quantizer is selected because there is a margin in the transmission path. On the contrary, when the number of frame skips 19 is small, a quantizer with a slightly coarser number is selected. FIG. 10 shows an example of preferable characteristics of the quantization step with respect to the number of frame skips. As the number of frame skips increases, the number of quantization steps becomes finer. The numerical value of the number of frame skips in the figure is merely an example and is not limited to this.

The macroblock significant information 21 is applied to the switch 6e, which in the case of a significant macroblock turns on this switch 6e to quantize the prediction error for that macroblock, but in the case of a non-significant macroblock this switch 6e. Is off and the prediction error for that macroblock is not quantized. Since other operations of the encoding engine unit 6 are known, description thereof will be omitted.

The quantized data 22 of the frame obtained by the encoding engine unit 6 (in the case of a significant macroblock),
Motion vector information 9 and macroblock significant information 21
Is encoded by the variable length encoding unit 23 (step S2
1), output from the code output unit 25 on the transmission path through the output buffer memory unit 17. Then similar operations from step S2 are repeated for the next frame.

As described above, according to this embodiment, with respect to an insignificant macroblock that transmits only a motion vector, the scalar length of the motion vector is reduced within the range in which the macroblock is determined to be insignificant. , The amount of generated motion vector information can be suppressed.

Also, by determining the number of frame skips before encoding the frame of interest, it is possible to determine the number of frame skips that makes full use of the characteristics of the image. As a result, it becomes possible to predict the amount of information of an image in advance and control the frame rate, and it is possible to perform variable frame rate image coding with constant quality. Further, since the motion vector information can be used for controlling the frame rate, it is possible to obtain a visually natural motion image.

The embodiments described above all show the present invention by way of example and not by way of limitation, and the present invention can be embodied in other various modifications and alterations. Therefore, the scope of the present invention is defined only by the claims and their equivalents.

[0049]

As described in detail above, according to the present invention, since the motion vector having the smallest size is selected within the range in which the macroblock to be coded is determined to be insignificant, only the motion vector is selected. , The amount of motion vector information to be transmitted is reduced, and the amount of transmitted information can be reduced.

The threshold value is determined by a function including the size of the motion vector as a parameter, and the function is a function that decreases when the size of the motion vector increases, or decreases when the size of the motion vector increases and the motion vector decreases. By using a function that saturates when a certain value is exceeded, the smaller the motion vector, the easier it is to determine as a non-significant macroblock.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a configuration of an embodiment of a moving image encoding device of the present invention.

FIG. 2 is a flowchart illustrating main operations in the embodiment of FIG.

FIG. 3 is a conceptual diagram of an operation of a motion vector generation unit.

FIG. 4 is a conceptual diagram of an operation of a macroblock significance judgment unit.

FIG. 5 is a characteristic diagram of a macroblock significance judgment threshold value.

FIG. 6 is a characteristic diagram showing an example of preferable characteristics of the number of frame skips with respect to a significant macroblock ratio.

FIG. 7 is a characteristic diagram illustrating an example of preferable characteristics of the number of frame skips with respect to the scalar length of a motion vector.

FIG. 8 is a characteristic diagram showing an example of preferable characteristics of the number of frame skips with respect to the amount of generated information up to immediately before.

FIG. 9 is a characteristic diagram showing a preferable characteristic of the number of frame skips in a three-dimensional manner.

FIG. 10 is a characteristic diagram showing an example of preferable characteristics of a quantization step with respect to the number of frame skips.

[Explanation of symbols]

1 Variable Frame Rate Video Coding Device 2 Video Signal Input Unit 3 Frame Skip Unit 4, 6j Frame Memory 6 Encoding Engine Unit 6a, 6b Mode Switch 6c, 13 Subtractor 6d Adder 6e Switch 6f DCT (Discrete Cosine Transform) Circuit 6g Q (quantization circuit) 6h Q ^-1 (inverse quantization circuit) 6i IDCT (inverse discrete cosine transform) circuit 6k, 8 motion compensation unit 11 motion vector generation unit 15 macroblock significant / insignificant determination unit 17 output buffer Memory unit 20 Frame skip number determination unit 23 VLC (Variable length coding unit) 25 Code output unit

Claims (10)

[Claims] 1. A motion compensation is performed on a macroblock of a previous frame using a generated motion vector, and a prediction error, which is a difference between the motion-compensated macroblock and an encoding target macroblock of the current frame, is calculated. Then, the calculated prediction error is compared with a threshold to determine whether the macroblock to be encoded is a non-significant macroblock smaller than the threshold or a significant macroblock larger than the threshold. It is a moving picture coding method that performs coding and transmits only the motion vector in the case of a non-significant macroblock, which is the smallest within the range in which the coding target macroblock is determined to be non-significant. A moving picture coding method characterized by selecting a motion vector of a size. 2. The motion vector is generated by sequentially increasing the motion vector from the smallest size, and each time the motion vector is generated, motion compensation is performed using the generated motion vector,
The method according to claim 1, characterized in that a prediction error is calculated and the calculated prediction error is compared with a threshold value to make the distinction between the significant and the insignificant. 3. The method according to claim 1, wherein the threshold value is determined by a function including a magnitude of a motion vector as a parameter. 4. The function according to claim 3, wherein the function decreases as the magnitude of the motion vector increases.
The method described in. 5. The method according to claim 3, wherein the function is a function that decreases as the magnitude of the motion vector increases and saturates when the motion vector exceeds a certain value. 6. A motion vector generation means for generating a motion vector, a motion compensation means for performing motion compensation on a macroblock of a previous frame using the generated motion vector, a macroblock for which motion compensation has been performed, and a current block. By calculating the prediction error that is the difference between the frame and the macroblock to be encoded, and comparing the calculated prediction error with a threshold, the macroblock to be encoded is an insignificant macroblock smaller than the threshold. A moving image provided with a determination means for determining whether there is a significant macroblock or a large significant macroblock, and a means for performing encoding if the macroblock is a significant macroblock, and transmitting only the motion vector if the macroblock is a non-significant macroblock. An encoding device, wherein the motion vector generating means is within a range in which the encoding target macroblock is determined to be insignificant. Video encoding apparatus, characterized in that the means for selecting the minimum size of the motion vector. 7. The motion vector generating means is means for sequentially increasing the motion vector from a motion vector having a minimum size and generating the motion vector, and the motion compensating means, the calculating means and the determining means are means for moving the motion vector. Each time a vector is generated, motion compensation is performed using the generated motion vector, a prediction error is calculated, and the calculated prediction error is compared with a threshold value to determine the significance and the non-significance. 7. The device according to claim 6, characterized in that 8. The apparatus according to claim 6, wherein the determination means has a function for including the magnitude of a motion vector as a parameter to determine the threshold value. 9. The function according to claim 8, wherein the function decreases as the magnitude of the motion vector increases.
An apparatus according to claim 1. 10. The apparatus according to claim 8, wherein the function is a function that decreases as the magnitude of the motion vector increases and saturates when the motion vector exceeds a certain value.