JPH03250886A - Video signal coding method - Google Patents

Abstract

PURPOSE:To suppress an unpleasant change in picture quality caused partially in a visual sense by selecting a block applying in-frame coding processing forcibly to each frame at random through the use of a random number. CONSTITUTION:A picture of one frame FRM is divided into prescribed number of blocks MB each comprising a prescribed number of picture elements, a block MB is selected at random for a prescribed period and subject to forcibly in- frame coding processing. That is, the block MB subject to forcibly in-frame coding processing for each frame FRM is selected at random by using a random number. Thus, the block MB subject to in-frame coding processing is not recognized in a visual sense and an unpleasant change in the picture quality caused partially in a visual sense is not made eminent.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Industrial field of application B. Overview of the invention C. Prior art (Figs. 9 to 11) D. Problems to be solved by the invention (Fig. 10) 8. Means for solving the problems (Figs. 1 and 11) Figure 8) F action (Figures 1 and 8) G embodiment (G1) Overall configuration of image information transmission system (Figures 1 to 5) (G2) Interframe/intraframe coding control (1st figure,
6 and 7) (G3) Forced refresh processing according to the embodiment (Fig. 1,
(Figures 3 and 8) (G4) Other embodiments H Effects of the invention A Field of industrial application The present invention relates to a video signal encoding method, and in particular to a method for encoding video signals with high efficiency and converting them into image data. It is commonly used and suitable.

B. Summary of the Invention The present invention provides a video signal encoding method that uses random numbers to randomly select blocks that are forcibly subjected to intra-frame encoding for each frame, thereby reducing the unsightly image quality that occurs partially. changes can be visually suppressed.

C. Conventional technology Conventionally, in video telephone systems and conference telephone systems, relatively severe limitations on transmission capacity have been imposed by highly efficient encoding of video signals consisting of moving images into intra-frame encoded data and inter-frame encoded data. A video signal transmission system has been proposed that transmits a moving picture video signal through a certain transmission path (Japanese Patent Application Laid-Open No. 1183/1983).

That is, for example, as shown in FIG. 9(A), at time t''
When trying to transmit the images PCI, PO2, PO2, etc. that make up the moving image in u+, tt, Ly, etc., the video signal has features with large autocorrelation over time. It is a process that increases transmission efficiency by compressing image data to be transmitted using a certain point, and intra-frame encoding processing is performed on images P, C1, PO2, PO2, etc. For example, the pixel data is compared with a predetermined reference value to find the difference, and thus each image PCI, PO2, PO2
. . . A compressed amount of image data is transmitted using autocorrelation between pixel data within the same frame.

In addition, as shown in FIG. 9(B), the interframe encoding process sequentially processes adjacent images PCI and PO2, PO2, and PO2.
2... Find image data PC12, PO23... consisting of the difference in pixel data between them, and use this as point 1.
The initial image PCI at = 1 + is transmitted together with the intra-frame encoded image data.

In this way, the images PCI, PO2, PO2, etc. can be encoded with high efficiency into digital data with a much smaller amount of data than in the case of transmitting all the image data, and can be sent to the transmission path. .

Such video signal encoding processing is executed in the image data generation device 1 having the configuration shown in FIG.

The image data generation device 1 processes the input video signal VD in the preprocessing circuit 2 to perform processing such as one field drop processing and one field line thinning processing, and then converts the luminance signal and chroma signal into 16 pixels (horizontally). ×16
It is converted into transmission unit block (referred to as a macroblock) data Sll consisting of data for pixels (in the vertical direction) and supplied to the image data encoding circuit 3.

The image data encoding circuit 3 generates interframe encoded data by receiving the predicted current frame data 312 formed in the predictive encoding circuit 4 and calculating the difference from the macroblock data S11, and converts the data into interframe encoding mode. or by determining the difference between the macroblock data Sll and the reference value data to form intra-frame encoded data and supply this as difference data 313 to the transform encoding circuit 5.

The transform encoding circuit 5 is constituted by a discrete cosine transform circuit, and sends out quantized image data S15 by supplying transform encoded data S14 obtained by performing orthogonal transformation on the difference data 313 and encoding it with high efficiency to the quantization circuit 6. let

The quantized image data 3 thus obtained from the quantization circuit 6
15 is subjected to high-efficiency encoding processing again in the retransformation encoding circuit 7 including a variable length encoding circuit, and then supplied to the transmission buffer memory 8 as transmission image data S16.

In addition, the quantized image data 315 is subjected to inverse quantization and inverse transform encoding processing in the predictive encoding circuit 4, and is decoded into difference data. After that, the pre-prediction frame data is corrected by the difference data. In addition to storing new pre-prediction frame data, the pre-prediction frame data stored in the predictive encoding circuit 4 is motion-compensated using motion detection data formed based on the macroblock data Sll, thereby generating the predicted current frame data. This allows the data to be generated and supplied to the image data encoding circuit 3, so that the difference between the macroblock data 311 of the frame to be currently transmitted (that is, the current frame) and the predicted current frame data S12 can be obtained as difference data 313. is being done.

In the configuration shown in FIG. 10, when transmitting the moving image described above with reference to FIG. 9, first, at time t in FIG.
1, the image data encoding circuit 3 enters the intra-frame encoding mode and supplies this as intra-frame encoded difference data 313 to the transform encoding circuit 5, and thereby the quantization circuit 6 , reconversion encoding circuit 7
The image data S16 is transmitted to the transmission buffer memory 8 via
supply.

At the same time, the quantized image data S15 obtained at the output end of the quantization circuit 6 is subjected to predictive encoding processing in the predictive encoding circuit 4, so that the pre-prediction data representing the transmission image data 316 sent to the transmission buffer memory 8 is Frame data is held in the previous frame memory, and then, at time t2, when macroblock data Sll representing the image PC2 is supplied to the image data encoding circuit 3, motion compensation is performed on the predicted current frame data S12, and the image data is encoded. circuit 3
is supplied to

Thus, at time j wa tt, the image data encoding circuit 3 generates the interframe encoded difference data 513.
is supplied to the conversion encoding circuit 5, whereby the difference data representing the change in the image between the frames becomes the transmission image data 31.
6 is supplied to the transmission buffer memory 8, and the quantized image data S15 is also supplied to the predictive encoding circuit 4, whereby pre-prediction frame data is formed and stored in the predictive encoding circuit 4.

The same operation is repeated thereafter, and while the image data encoding circuit 3 executes interframe encoding processing, only the difference data representing the change in the image between the previous frame and the current frame is stored in the transmission buffer memory. 8 will be sent out sequentially.

The transmission buffer memory 8 stores the transmission image data S16 sent out in this way, and sequentially draws out the stored transmission image data 316 as transmission data DTIAN3 at a predetermined data transmission rate determined by the transmission capacity of the transmission line 9. and transmit it to the transmission path 9 (.

At the same time, the transmission buffer memory 8 detects the amount of remaining data, feeds back the remaining amount data 317 that changes according to the amount of residual data to the quantization circuit 6, and performs a quantization step according to the remaining amount data 317. By controlling the size and adjusting the amount of data generated as the transmission image data 316, it is possible to maintain an appropriate remaining amount of data (an amount of data that does not cause overflow or underflow) in the transmission buffer memory 8. It is done like this.

Incidentally, when the remaining amount of data in the transmission buffer memory 8 increases to the permissible upper limit, the step size of the quantization step 5TPS (FIG. 11) of the quantization circuit 6 is increased based on the remaining amount data 317. By causing the quantization circuit 6 to perform coarse quantization, the transmitted image data 3
16 data amount is reduced.

On the contrary, when the remaining amount of data in the transmission buffer memory 8 decreases to the allowable lower limit value, the remaining amount data 317 controls the step size of the quantization step 5 TPS of the quantization circuit 6 to a small value. As a result, the quantization circuit 6
By performing fine quantization in the transmission image data 316, the amount of data generated in the transmitted image data 316 is increased.

D Problems to be Solved by the Invention As described above, the conventional image data generation device 1 is capable of generating the most data while matching the transmission conditions in which the data transmission speed of the transmission data D0 A transmission buffer memory 8 is provided as a means for efficiently transmitting significant image information, and the remaining data amount of the transmission buffer memory 8 is adjusted so that the remaining data amount of the transmission buffer memory 8 is always maintained in a state where it does not overflow or underflow. The quantization step size of the quantization circuit 6 is controlled accordingly, but if this continues, the transmission data D? , ,N, may become unsightly.

Incidentally, in the forced refresh process, the image data that has been subjected to the intra-frame encoding process is transferred to the transmission data D4.

If you continue to transmit image data that has been interframe encoded for a long time based on this,
If even one bit of transmission error occurs during this period, the image data encoding circuit 3 By forcibly switching to the intra-frame encoding mode, the intra-frame encoded data, which is the reference for decoding the image data, is sent out as the transmission data DTlAN3 on the receiving side, and the data is stored in the predictive encoding circuit 4. (This operation is called forced refresh mode).
Publication No. 6).

The present invention has been made in view of the above points, and it is an object of the present invention to propose a video signal encoding method that visually suppresses unsightly changes in image quality and enables forced refresh processing to be executed. be.

Means for Solving the E1m Problem In order to solve this problem, the present invention selects intra-frame coding or inter-frame coding to convert the video signal VD.
Transmission image data 340 is generated by encoding the IN.
In the video signal encoding method for converting l frame F
Divide the RM image into a predetermined number of blocks MB each having a predetermined number of pixels, randomly select the blocks MB at a predetermined period,
The selected block MB is subjected to intraframe encoding processing.

2 Effects By randomly selecting a block MB that is forcibly subjected to intra-frame encoding processing for each frame FRM using random numbers, the block MB that is subjected to intra-frame encoding processing is made visually unrecognizable. This makes it possible to make unsightly changes in image quality that occur locally less noticeable.

Embodiment G An embodiment in which the present invention is applied to a videophone will be described in detail below with reference to the drawings.

(G1) Overall configuration of image information transmission system In FIGS. 1 and 2, the image information transmission system 21 includes an encoder 2
1A and a decoder 21B, and the encoder 21A receives the input video signal VDIN from the input circuit section 2.
After the preprocessing in step 2, the analog/digital conversion circuit 23 sends the transmission unit block data consisting of pixel data of 16×16 pixels, that is, the input image data 321 consisting of the pixel data of the macro block MB, to the pixel data processing system SYMI. At the timing when pixel data is processed in units of macroblocks MB in each processing stage of the pixel data processing system SYMI, processing information data corresponding to the processed data is sequentially transmitted via the Herada data processing system SYM2. Thus, pixel data and header data are sent to the pixel data processing system SYMI and the header data processing system S, respectively.
In YM2, the row (.

In the case of this embodiment, macroblock data sequentially sent out as input image data S21 is extracted from frame image data FRM by a method as shown in FIG.

First, input video signal VDIN has QCIF picture size (1
76 x 144 pixels), one frame image data FRM consists of two pieces (
The block group GOB is divided into 11 (horizontally) x 3 (vertically) block groups GOB as shown in FIG. 3(B). macroblocks MB, and each macroblock MB has a size of 16X as shown in FIG. 3(C).
Luminance signal data for 16 pixels Y0° to Y, (8 pixels each
x8 pixels) and color signal data C1 and C, which are color signal data corresponding to all pixel data of the brightness signal data Yo0 to Yll.

On the other hand, the second input video signal V D I N is
When the image size is F (252 x 288 pixels), one frame image data FRM is divided into 2 (horizontally) x 6 (vertically) block groups GOB as shown in Figure 3 (A2). divided, each block group GO
B is 11 pieces (horizontally) as shown in Figure 3 (B)
It is configured to include three macroblocks MB (in the vertical direction), and each macroblock MB has luminance signal data Y for 16×16 pixels, as shown in FIG. 3(C). ~Y...
(each consisting of luminance signal data for 8×8 pixels) and color signal data C1 and C2 consisting of color signal data corresponding to all pixel data of the luminance signal data Y, %Y, .

In this way, the input image data S21 sent for each macroblock MB is given to the motion compensation circuit 25, and the motion compensation circuit 25 receives motion detection control given from the motion compensation control unit 26 provided for the Helada data processing system SYM2. In response to the signal 322, the pre-prediction frame memory 2
7 pre-prediction frame data S23 and input image data 32
1 to detect the motion vector data MVD (x) and *vocy) and supply it to the motion compensation control unit 26 as data of the first hellada data HDI (FIG. 4). , motion vector data MVD is applied to the pre-prediction frame data 323.
(x) and MVD (y) to form predicted current frame data 324 and supply it to the image data encoding circuit 28 together with current frame data 325 consisting of input image data 321 that is currently being processed. .

Here, the motion compensation control unit 26, as shown in FIG.
r and its block group GOB (Figure 3 (A1)
, (A2))
address and its macroblock MB
Macroblock number data MB address
By adding , sequential pixel data processing system SYM
The macroblock MB transmitted to each processing stage of I is displayed, and flag data FLAGS representing the processing or processing format of the macroblock MB to be processed and motion vector data VD of the macroblock MB are displayed. (x) and MVD (y), and difference data Σl A-B l representing their evaluation values are formed.

As shown in FIG. 5, the flag data FLAGS is designed to have flags for a maximum of l words (16 bits), and the O-th bit contains the macroblock M to be processed.
A motion compensation control flag MConloff indicating whether or not B should be processed in motion compensation mode is set.

In addition, the first bit of the flag data FLAGS contains interframe/intraframe information indicating whether the macroblock MB to be processed should be processed in interframe coding mode or intraframe coding mode. Flag I
ter/intra is set.

Further, a filter flag Filter onloff indicating whether or not to use the loop filter 25B of the motion compensation circuit 25 is set in the second bit of the flag data FLAGS.

Furthermore, the third bit of the flag data FLAGS contains the block data Yo0 included in the macroblock to be processed.
-C, (FIG. 3(C)) can be set with a transmission flag Coded/Not-coded indicating whether or not to be transmitted.

Further, the fourth bit of the flag data FLAGS can be set with a drop frame flag indicating whether or not to drop frames of the macroblock MB to be processed.

Furthermore, the fifth bit of the flag data FLAGS contains a forced refresh flag Refresh on indicating whether or not to forcibly refresh the macroblock MB to be processed.
loff can be set.

Furthermore, the sixth bit of the flag data FLAGS contains the macroblock power evaluation flag -BP aρprecia
te can be set.

Further, the difference data ΣIA-Bl is the current frame data 32
5, macroblock data A to be currently processed,
It represents the minimum value of the difference between the pre-prediction frame data S23 and the macroblock data B compensated by the motion vector for detection, so that the detected motion vector can be evaluated.

The image data encoding circuit 28 supplies the current frame data S25 given from the motion compensation circuit 25 as is as difference data S26 to the transform encoding circuit 29 in the intraframe encoding mode, and in contrast, in the interframe encoding mode. At this time, difference data 826 consisting of the difference between the pixel data of the current frame data S25 and the pixel data of the predicted current frame data 324 is supplied to the transform encoding circuit 29.

The header data processing system SYM2 is provided with a frame related/intraframe encoding control unit 30 corresponding to the image data encoding circuit 28, and a motion compensation control unit 26.
Based on the header data HDI supplied from the image data encoding circuit 28 and the calculation data 531 supplied from the image data encoding circuit 28, an interframe/intraframe flag Enter/In is used to specify the encoding mode of the image data encoding circuit 28.
tra (FIG. 5) and a filter flag F for controlling the operation of the loop filter 25B of the motion compensation circuit 25.
The data necessary to obtain the filter onloff (FIG. 5) is calculated and sent to the filter control unit 31 as the second filter data HD2.

As shown in FIG. 4, the second header data HD2 includes transmission frame number data T constituting the header data HDI.
RCounter~Difference data Σl Power data Σ(A) necessary for inheriting A-B as is and forming interframe/intraframe encoding mode switching signal 333 and filter on/off signal 334 in filter control unit 31 (L) and Σ(A)”(H)
, Σ(A-B)" (L) and Σ(A-B)" (H)
, Σ(A-FB)"(L) and Σ(A-FB)"(H
), Σ(A) are added in the interframe/intraframe coding control unit 30.

Here, the power data Σ(A)"(L) and Σ(A)"
(H) represents the lower bit and upper bit of the sum of squares of the macroblock pixel data A of the current frame data 325,
Power data Σ(A-B)” (L) and Σ(A-B)
” (H) is the lower bit of the sum of squares of the difference A-B between the macroblock pixel data A of the current frame data S25 and the macroblock pixel data B of the predicted current frame data S24 formed without going through the loop filter 25B. The power data Σ(A-FB)" (L) and the power data Σ(A-FB)" (H) represent the current frame data S2.
5 macroblock pixel data A and loop filter 25
The power data Σ(
A) represents the sum of macroblock pixel data A of the current frame data 325, and the amount of data is expressed as a power value in order to evaluate the size of the data to be processed (the sum of squares is expressed as a value independent of sign). ).

The filter f1ii1?11 unit 31 receives the second
Based on the frame data HD2 and the remaining amount data S32 supplied from the transmission buffer memory 32, an interframe/intraframe encoding mode switching signal S33 is sent to the image data encoding circuit 28, and the loop filter A filter on/off signal 334 is sent to 25B, and a filter flag Filter onloff representing the contents of the filter on/off signal S34 is added to the second hellada data HD2 to perform threshold control as third hellada data HD3. Pass to unit 35.

Here, the filter control unit 31 first controls the image data encoding circuit 28 when the amount of data to be transmitted when performing interframe encoding processing is larger than the amount of data to be transmitted when performing intraframe encoding processing. Control to intraframe coding mode.

Further, the filter control unit 31 secondly controls the predicted current frame data S that has been processed in the loop filter 25B while processing in the interframe coding mode.
Predicted current frame data S2 that is not subjected to the processing from 24
If the difference value is smaller in 4, the loop filter 25B is controlled by the filter on/off signal 334 so as not to perform the filtering operation.

Thirdly, when the filter control unit 31 enters the forced refresh mode, it switches the image data encoding circuit 28 to the intraframe encoding mode using the interframe/intraframe encoding mode switching signal S33.

Furthermore, the filter control unit 31 fourthly detects when the transmission buffer memory 32 is in a state where there is a risk of overflow based on the remaining amount data 332 supplied from the transmission buffer memory 32 and performs a preventive process. The third radar data HD3 containing flags instructing what to do is sent to the threshold control unit 35.

In this way, the image data encoding circuit 28 encodes the difference data S2 in a mode that minimizes the difference between the current frame data 325 and the predicted current frame data S24.
6 is supplied to the transform encoding circuit 29.

As shown in FIG. 4, the third header data HD3 includes transmission frame number data TRCo from the header data HD2.
unter ~ motion vector data VD(X) and gate ν
In addition to taking over D(y), the filter control unit 31
At this point, a 6-bit filter flag Filter onloff corresponding to the block data Y0° to C4 is added.

The transform encoding circuit 29 is a discrete cosine transform circuit, and converts the coefficient value after the discrete cosine transform into 6
blocks Y. , Y06, Yl. ,Yo,C,,C
, transform encoded data 5 obtained by zigzag scanning for each
35 to the transmission block setting circuit 34.

The transmission block setting circuit 34 receives six block data Y sent out as converted encoded data S35. . ~C,
(FIG. 3(C)), calculate the sum of squares of up to n coefficients from the first coefficient data, and use the calculation results as power detection data 336 to the threshold control unit 35.
give it to

At this time, the threshold control unit 35 compares the power detection data S36 with a predetermined threshold for each block data Y0° to C1, and does not allow transmission of the block data when the power detection data S36 is smaller than the threshold. 6 bits of transmission permission/denial data CBPN indicating that it is allowed is formed when it is larger than that, and is added to the third hellada data HD3 passed from the filter control unit 31 and quantized as fourth hellada data HD4. The corresponding block data Y is passed from the transmission block setting circuit 34 to the control unit 36 . -C,
The block patterned data 33 is sent to the quantization circuit 37.
7.

Here, the fourth header data HD4 is the transmission frame number data TRC of the header data HD3, as shown in FIG.
outer~Filter flag Filter onlo
ff is taken over as is, and the threshold control unit 35 adds a 6-bit transmission permission flag CBPN generated corresponding to blocks Y0° to C, .

The quantization control unit 36 is the threshold control unit 3
5, and the remaining amount data 332 sent from the transmission buffer memory 32, the quantization step size control signal S38 is given to the quantization circuit 37. , This causes the quantization circuit 37 to perform quantization processing with a quantization step size adapted to the data included in the macroblock MB, and as a result, the quantized image data S39 obtained at the output end of the quantization circuit 37 is variable-length encoded. The circuit 38 is fed.

At the same time, as shown in FIG. 4, the quantization control unit 36 respectively corresponds to the block data Y00 to C (FIG. 3(C)) as the fifth header data HD5 based on the header data HD4. Flag data FLAG
S and motion vector data 1D (x) and MVD (
y) and arranged in series to form data, which is passed to the variable length encoding circuit 38 and the inverse quantization circuit 40.

Here, the header data HD5 is as shown in FIG.
Transmission frame number data TR of header data HD4
Counter ~ Macroblock number data MB ad
At the same time, the quantization control unit 36 takes over the quantization size data QNT and the flag data FLAGS for the block data Y0° to CP.
, motion vector data MVD (X) and MVD (
Add y).

The variable length encoding circuit 38 performs variable length encoding processing on the Hellada data HD5 and the quantized image data 339 to form transmission image data S40, and supplies this to the transmission buffer memory 32.

The variable length encoding circuit 38 encodes block data Yoo to C, .
When performing variable length encoding, the corresponding flag data FLA
When "drop-proof" or "untransmittable" is specified based on the GS, the block data is transmitted as image data 3.
40 and discards it without sending it.

The transmission buffer memory 32 accumulates the transmission image data S40, reads it out at a predetermined transmission speed, and sends it to the audio data generator 42 in the multiplexer 41.
It is combined with transmission audio data 541 sent out from the transmission line 43 and sent out to the transmission path 43.

The dequantization circuit 40 dequantizes the quantized image data S39 sent from the quantization circuit 37 based on the header data HD5, and then supplies the dequantized data S42 to the inverse transform encoding circuit 43. Inverse transform encoded data S
43 and then supplied to the decoder circuit 44, and the encoded difference data 344 representing the image information thus sent out as the transmission image data 340 is stored in the pre-prediction frame memory 2.
7 to be supplied.

At this time, the pre-prediction frame memory 27 uses the encoded difference data S44 to modify the previously stored pre-prediction frame data and stores it as new pre-prediction frame data.

Thus, according to the encoder 21A having the configuration shown in FIG. 1, pixel data is pipeline-processed in macroblock units in the pixel data processing system SYM1 based on the header information supplied from the header data processing system SYM2. , the header data processing system S is synchronized with this.
By receiving and passing the ladder data to YM2, pixel data can be adapted as necessary by adding or deleting header data as necessary at each processing stage of the header data processing system SYM2. Can be processed.

As shown in FIG. 2, the decoder 21B transfers the transmission data transmitted from the encoder 21A via the transmission line 43 to the transmission buffer memory 52 via the demultiplexer 51.
At the same time, the transmitted audio data 351 is received by the audio data receiving device 53.

The image data received in the transmission buffer memory 52 is separated into received image data S52 and header data HDII in a variable length inverse transform circuit 54, dequantized into dequantized data 353 in a dequantization circuit 55, and then converted into inverse transform code. The data is subjected to discrete inverse transformation processing in the encoding circuit 56 and is inversely transformed into inversely transformed encoded data 354.

This inversely transformed encoded data S54 is given to the decoder circuit 57 together with the header data HD12 formed in the inverse quantizer 55, and is stored in the frame memory 58 as encoded difference data S55.

Thus, the encoded difference data 35 is stored in the frame memory 58.
The image data transmitted based on 5 is decoded,
The decoded image data 356 is converted into an analog signal in the digital/analog conversion circuit 59, and then sent out as an output video signal (Doua) via the output circuit section 60.

(G2) Interframe/intraframe coding control The interframe/intraframe coding control unit 30 performs interframe coding processing or frame coding based on the weight of the image to be currently processed and the weight of the prediction error. Inner encoding processing is selected.

That is, the pixel data at the (i, j) coordinates of the macroblock to be currently processed in the current frame data 325 is converted to A(
i, D, the macroblock data A to be currently processed in the current frame data 325 represented by the power data Σ(A) is expressed by the following equation, and the power data Σ(A)'' (L), Σ( The sum of squares A2 of the macroblock data represented by A)"(H) is expressed by the following equation, and the detection motion vector data MVD (x) and -VD(
If the pixel data at the ci and D coordinates of the macroblock compensated by B (i, j, x, y) is the power data Σ(A-B)"
The sum of squares (A-B) of the difference data of macroblock data A and B represented by (H) is represented by the following formula (%) (3), and furthermore, and loop filter 25B
The pixel data at the (i, j) coordinates of the macroblock of the predicted current frame data S24 formed through
(i, j, x, power data Σ(A-FB
)"(L), Σ(A-FB)" (H) The sum of squares of the difference data of macroblock data A and FB (A-FB)" is calculated by the following formula (%) (4) (However, when the motion compensation mode is not executed, x=y=o).

Therefore, from equations (1) and (2), the weight VAROR of the image to be currently processed is expressed by the following equation, and further, from equation (3), the weight VAR of the prediction error when no loop filter is used is expressed by the following equation. Furthermore, from equation (4), the weight FVAR of the prediction error when using the loop filter is expressed by the following equation.

Therefore, the filter control B unit 31 selects and specifies the interframe coding mode or the intraframe coding mode based on the weight of the macroblock MB that has been weighted in this manner.

In other words, when the motion compensation mode is not executed (when a loop filter is not used), as shown in FIG. If it is in the shaded area 1ntra, the filter control unit 31 controls the image data encoding circuit 28 to be in intra-frame encoding mode, and if it is in another area Inter, it is controlled to be in inter-frame encoding mode. .

Thus for interframe coding mode A(i,j)
-B (i, j, x, y), and in the case of intra-frame encoding mode, A (i, j) can be encoded to efficiently transmit image data.

On the other hand, when executing the motion compensation mode (that is, when using a loop filter), the weight VAROR of the image to be currently processed and the weight FVAR of the prediction error when using the loop filter are When the area to be determined is in the shaded area 1ntra, the filter control unit 31 controls the image data encoding circuit 28 to the intra-frame encoding mode, and
If it is, it is controlled to interframe coding mode.

Thus for interframe coding mode A(i,j)
- By encoding F B (i, j, x, y) and motion vector data MVD (X), MVD (y), and in the case of intra-frame encoding mode, by encoding A (i, D), the image Data can be transmitted efficiently.

In this way, the filter control unit 31 can perform switching between the interframe coding mode and the intraframe coding mode based on the weight of the macroblock.

(G3) Forced refresh processing according to the embodiment After specifying the interframe coding mode or the intraframe coding mode for each macroblock MB, the filter control unit 31 executes forced refresh processing for a predetermined macroblock MB.

In other words, when encoding image data having the image size of QCIF (Fig. 3 (Al)), the filter control unit 31 has a function corresponding to all macroblocks MB of one frame image, as shown in Fig. 8. and 99 counters C
NTs are arranged, and at the time of initial setting, values from 0 to 98 are randomly assigned to each counter using random numbers to form a predetermined refresh pattern.

When the encoding operation is started in this state, if the value of the corresponding counter is 97 or less when each macroblock data is input, the corresponding counter is incremented.

The value of the counter incremented in this way is 9
When the count reaches 8, the interframe/intraframe flag of the flag data FLAGS of the macroblock corresponding to the counter is designated as "0", and the macroblock is forcibly processed in the intraframe coding mode. At the same time, the value of the counter is returned to 0.

By forcibly switching one macro program per frame to the intra-frame encoding mode and encoding (that is, forcing refresh), all macroblocks are refreshed.

By repeatedly executing the forced refresh in this way, the screen is always refreshed when 99 frames of data have been processed.

Therefore, even if a transmission error occurs and the quality of the image decoded on the decoder 21B side deteriorates, even if image data subjected to interframe coding continues to be transmitted for a long time, the 99-frame Deterioration in image quality is corrected by refreshing all macroblocks while one frame's worth of image data is being transmitted.

The macroblock MB subjected to forced litzchase may be quantized with a quantization step size different from that of other macroblocks, and in such cases, only the forcedly refreshed macroblock portion is displayed on the image. This will cause an unsightly change in image quality, but
By forming the refresh pattern (FIG. 8) in the filter control unit 31 using random numbers, each macroblock MB is forcefully refreshed at random.
It is possible to make a partially obtrusive change in the two awards less noticeable.

In this way, it is possible to perform a forced refresh while visually suppressing changes in image quality that are unsightly.

By the way, forced refresh is not performed on the frames that are to be processed after being dropped, and by reliably refreshing only the image data that is transmitted to the receiving side, the image data for 99 frames that are transmitted can be saved. per l
A frame's worth of macro blocks is reliably refreshed.

(G4) Other Embodiments In the embodiments described above, the present invention is applied when encoding and transmitting an image having a QCIF image size, but the present invention is not limited to this. The present invention can also be applied to the case of encoding an image having the image size (FIG. 3 (A2)).

In this case, four macroblocks are associated with each refresh counter shown in FIG.
All you have to do is force refresh of one macroblock.

Furthermore, in the above-described embodiment, a case where forced refresh is performed using the refresh pattern shown in FIG. obtain.

Further, in the above-described embodiment, the present invention is applied to an image information transmission system that transmits a video signal together with an audio signal, but the present invention is not limited to this, and the present invention is not limited to this. Can be widely applied to transmission, etc.

H Effects of the Invention As described above, according to the present invention, by forming a refresh pattern using random numbers, it is possible to forcibly refresh each macroblock at random, thereby eliminating the eyesore that occurs partially. It is possible to visually suppress changes in both pages.

[Brief explanation of drawings]

1 and 2 are block diagrams showing an encoder and a decoder constituting an image information transmission system to which the video signal encoding method according to the present invention is applied, FIG. 3 is a route map showing the structure of frame image data, and FIG. The figure is a block diagram showing the Herada data processing system in Figure 1, Figure 5 is a route map showing the configuration of the flag data in Figure 4, and Figures 6 and 7 are interframe/intraframe encoding mode selection. A characteristic curve diagram showing the standard, FIG. 8 is a route map showing macroblock refresh patterns, FIG. 9 is a route diagram explaining intra-frame/inter-frame encoding processing, and FIG. 10 is a conventional image data generation device. FIG. 11 is a block diagram showing another quantization step; FIG. 21... Image information transmission system, 21A...
... Encoder, 21B ... Decoder, 25
... Motion compensation circuit, 26 ... Motion compensation control unit, 27 ... Pre-prediction frame memory, 28 ... Image data encoding circuit, 29 ...・
... Conversion encoding circuit, 30 ... ... Interframe/
Intraframe encoding control unit, 31... Filter control unit, 32... Transmission buffer memory, 34... Transmission block setting circuit, 35...
...Threshold control unit, 36...
Quantization control unit, 37...Quantization circuit, 3
8...Variable length encodeable circuit.

Claims (1)

[Claims] In a video signal encoding method that converts a video signal into transmission image data by selecting intra-frame encoding or inter-frame encoding and encoding the video signal, one frame of image is encoded with a predetermined number of pixels. What is claimed is: 1. A video signal encoding method, comprising: dividing the video signal into a predetermined number of blocks, randomly selecting the blocks at a predetermined period, and subjecting the selected blocks to intra-frame encoding processing.