JPH03250884A - Video signal encoder - Google Patents

Abstract

PURPOSE:To obtain a video image smooth in a visual sense by executing a de-frame processing till a data residual value is decreased to a prescribed data residual value less than a prescribed upper limit when a data residual capacity of a transmission buffer memory exceeds the prescribed upper limit capacity. CONSTITUTION:A transmission picture data S4O subject to high efficient coding processing is once stored in a transmission buffer circuit 32 and the stored transmission picture data S40 stored based on the data transmission capacity of the transmission line 43 is sequentially outputted to a transmission line 43. When the data residual capacity Buffer of the transmission buffer circuit 32 exceeds a prescribed upper limit, the de-framing processing of the transmission picture data S40 is executed and when the data residual capacity Buffer of the transmission buffer circuit 32 is decreased to a prescribed object level less than the upper limit, the de-framing picture is finished. Thus, a video image moved smoothly in a visual sense is obtained.

Description

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

A. Industrial field of application B. Outline of the invention C. Conventional technology (Figures 8 to 10) D. Problems to be solved by the invention E1m! Means for solving N (Figures 1 and 6)
F effect (Figs. 1 and 6) G embodiment (G1) Overall configuration of image information transmission system (Figs. 1 to 5) (G2) Frame drop processing according to the embodiment (Figs. 1 and 4) , FIG. 5, FIG. 6, and FIG. 7) (G3) Other Embodiments H Effects of the Invention A Industrial Application Field The present invention relates to a video signal encoding device, for example, converting a video signal into highly efficient encoded data. This is suitable for application when converting and transmitting.

B. Summary of the Invention The present invention provides a video signal encoding device that, when performing frame dropping processing according to the remaining data amount in a transmission buffer memory, performs frame dropping processing on a data remaining amount value at which frame dropping processing is started. By setting the remaining data amount value at the end of the process to a small level, the movement of the transmitted image can be made visually smoother.

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. 8(A), at time L-
When trying to transmit each image PCI, PO2, PO3, etc. that constitutes a moving image in L+, Lx, js, etc., the video signal has a large autocorrelation as time passes. It is a process that improves transmission efficiency by compressing image data to be transmitted using certain characteristics, and intra-frame encoding processing is performed using image PCI, PO2, PO3, etc. For example, compression processing is performed to compare the pixel data with a predetermined reference value to find the difference, and thus each image PCI, PO2, PO3,
. . . A compressed amount of image data is transmitted using autocorrelation between pixel data within the same frame.

In addition, as shown in FIG. 8(B), the interframe encoding process sequentially processes the adjacent images
3... Obtain image data PC12, PO23... consisting of the difference in pixel data between
The initial image PCI at −1+ is transmitted together with the image data subjected to intraframe encoding processing.

In this way, the images PCI, PO2, PO3, etc. can be encoded with high efficiency into digital data with a much smaller amount of data than in the case of transmitting all of 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 divides the luminance signal and chroma signal into 16 pixels (horizontally )X16
It is converted into transmission unit block (referred to as a macroblock) data 311 consisting of data for 1i elements (in the vertical direction) and is 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 S12 formed in the predictive encoding circuit 4, and calculates the difference between it and the macroblock data 311, and converts the data into interframe encoding mode. or by determining the difference between the macroblock data 311 and the reference value data to form intra-frame encoded data, which is supplied to the transform encoding circuit 5 as difference data S13.

The transform encoding circuit 5 is constituted by a discrete cosine transform circuit, and provides transform encoded data S14, which is highly efficiently encoded by orthogonally transforming the difference data S13, to the quantization circuit 6, thereby converting the quantized image data S15.
send out.

The quantized image data S obtained from the quantization circuit 6 in this way
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 316.

In addition, the quantized image data S15 is subjected to inverse quantization and inverse transform encoding processing in the predictive encoding circuit 4, so that after being decoded to difference data, the pre-prediction frame data is corrected using the difference data. The new pre-prediction frame data is stored, and the pre-prediction frame data stored in the predictive encoding circuit 4 is motion-compensated using the motion detection data formed based on the macroblock data Sll, thereby creating the predicted current frame data. As a result, 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 312 is generated as difference data S13. It is made to be obtained.

In the configuration shown in FIG. 9, when transmitting the moving image described above with reference to FIG. 8, first, at time t1 in FIG.
, the image data encoding circuit 3 enters the intra-frame encoding mode and supplies this to the transform encoding circuit 5 as the intra-frame encoded difference data 313, whereby the quantization circuit 6, The transmission image data S16 is supplied to the transmission buffer memory 8 via the reconversion encoding circuit 7.

At the same time, the quantized image data 315 obtained at the output end of the quantization circuit 6 is subjected to predictive coding processing in the predictive coding circuit 4, so that the pre-prediction data representing the transmission image data S16 sent to the transmission buffer memory 8 is Frame data is held in the previous frame memory, and subsequently, when macroblock data Sll representing the image PC2 is supplied to the image data encoding circuit 3 at time t=, motion compensation is applied to the predicted current frame data 312 and the image data is encoded. conversion circuit 3
is supplied to

Thus, at time t ``'' T, z, the image data encoding circuit 3 outputs the difference data S that has been subjected to the interframe encoding process.
13 is supplied to the transform encoding circuit 5, and thereby the difference data representing the change in the image between the frames is supplied to the transmission buffer memory 8 as the transmission image data S16, and the quantized image data 315 is predictively encoded. By being supplied to the circuit 4, 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 316 sent out in this way, and sequentially transfers the stored transmission image data 516 to the transmission data D address at a predetermined data transmission rate determined by the transmission capacity of the transmission line 9. . The signal is closed, pulled out, and transmitted to the transmission line 9.

At the same time, the transmission buffer memory 8 detects the amount of remaining data, feeds back the remaining amount data 517 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 S17. 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 allowable upper limit, the step size of the quantization step 5TPS (Fig. 1O) of the t-quantization circuit 6 is increased according to the remaining amount data S17. By performing coarse quantization in the quantization circuit 6, the transmitted image data S
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 S17 controls the step size of the quantization step 5TPS 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 However, in the image data generation device 1 having the above configuration, when the moving image to be transmitted is an image with rapid movement, or the content of the image changes greatly, for example, due to a scene change, etc. In the above, there was a problem that the transmission buffer memory overflowed due to an increase in the amount of encoded transmission data generated.

As one method to solve this problem, a method has been considered in which when the amount of transmitted data increases, frames are dropped without being encoded.

However, when images with rapid movement are transmitted for a relatively long period of time, the amount of transmitted data continues to increase during this period, resulting in frequent frame drops, and the smoothness of the motion in the reproduced moving image becomes visually impaired. There are problems that need to be worked out, and it is still insufficient for transmitting moving images.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a video signal encoding device that is capable of dropping frames while visually making the motion of a moving picture as smooth as possible.

E! I! ! Means for Solving I In order to solve this problem, the present invention includes a transmission buffer circuit 32, in which transmission image data 340 that has been subjected to high efficiency encoding processing is temporarily stored, and then transmitted. In a video signal encoding device (21) that sequentially outputs transmission image data S40 stored on the transmission path 43 based on the data transmission capacity of the transmission path 43, the data remaining amount value Buffer of the transmission buffer circuit 32 is set to a predetermined upper limit value ( QN
T = 31), frame dropping processing of the transmission image data S40 is executed, and the data remaining amount value Buffer of the transmission buffer circuit 32 is set to a predetermined target value level MC( QNT = 1)
When the number of frames decreases to , the frame dropping process is terminated.

When the data remaining amount Buffer of the F-action transmission buffer circuit 32 exceeds the upper limit value (QNT = 31), after specifying the execution standby of frame drop processing, the data remaining amount Buffer exceeds the upper limit value (QNT = 31).
Target value MG (QNT =
By specifying the end of frame dropping processing when the value falls below 1), the data remaining amount value Buf is set after the frame dropping processing is completed.
Even if fer increases rapidly, it is possible to avoid restarting the frame dropping process immediately, and when the amount of data generation decreases after the frame dropping process is finished, the remaining data amount Buffer can be quickly adjusted to the target value MC. (QNT-1)
can be converged to.

In this way, the movement of the output image can be visually smoothed, and deterioration of both prizes can be avoided.

C example An embodiment of the present invention 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 preprocesses the input video signal VD+N in the input circuit section 22, and then converts the input video signal VD+N into an analog/digital conversion circuit 23.
At this time, transmission unit block data consisting of pixel data for 16 x 16 pixels, that is, input image data S21 consisting of pixel data of the macro block MB, is sent to the pixel data processing system SYMI, and the pixel data processing system S
At the timing when pixel data is processed in units of macroblocks MB in each processing stage of YMI, processing information data corresponding to the data to be processed is sequentially transmitted via the Herada data processing system SYM2. Pixel data and header data are processed by pixel data processing system SYMI and header data processing system SY, respectively.
In M2, processing is performed in a pipeline manner.

In the case of this embodiment, macroblock data sequentially sent out as input image data 321 is extracted from frame image data FRM using a method as shown in FIG.

First, one frame image data FRM is divided into 2 (horizontally) x 6 (vertically) block groups COB as shown in FIG. 3(A), and each block group GOB is divided into block groups COB as shown in FIG. As shown in FIG. 3(B), it includes 11 (horizontally) x 3 (vertically) macroblocks MB, and each macroblock MB has 16×16 pixels as shown in FIG. 3(C). Luminance signal data Y0゜～
Y, □ (each consisting of luminance signal data for 8×8 pixels) and color signal data C5 and C, consisting of color signal data corresponding to all pixel data of luminance signal data Y0° to Y11,
Contains.

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 S22, 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 MVD (y) and supply them to the motion compensation control unit 26 as data of the first hellada data MDI (FIG. 4). 25A, motion vector data MV is added to the pre-prediction frame data 323.
By performing motion compensation for D (X) and MVD Cl), predicted current frame data 324 is formed and is supplied to the image data encoding circuit 28 together with current frame data S25 consisting of input image data 521 that is currently being processed. .

Here, the motion compensation control unit 26, as shown in FIG.
r and its block group GOB (Figure 3 (A))
Block group number data representing GOB address
ss and macroblock number data MB address representing one of the macroblocks MB, thereby displaying the macroblocks MB that are sequentially transmitted to each processing stage of the pixel data processing system SYMI. Macroblock MB to be processed
flag data FLAGS representing the processing or processing format of the macroblock MB; and motion vector data MVD of the macroblock MB.
(x) and MVD(y), and difference data ΣA−B l representing their evaluation values are formed.

As shown in Fig. 5, the flag data FLAGS can be up to 1
It is possible to have flags for 111 words (16 bits), and a motion compensation control flag MConloff indicating whether or not the macroblock MB to be processed should be processed in motion compensation mode is set in the 0th bit.

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 1
inter/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 a transmission flag Coded/, which indicates whether or not the block data Y0° to C, , (FIG. 3(C)) included in the macroblock to be processed is to be transmitted. Not-coded can be set.

Further, the fourth bit of the flag data FLAGS can be set with a frame drop flag Drop fra+me flag, which does not indicate whether or not the macroblock MB to be processed is to be dropped.

Further, the fifth bit 12 of the flag data FLAGS is a forced refresh flag Refresh o indicating whether or not to forcibly refresh the macroblock MB to be processed.
nloff can be set.

Furthermore, the sixth bit of the flag data FLAGS contains a macroblock power evaluation flag MBP appreciat
e can be set.

Further, the difference data ΣIA-Bl is the current frame data S2
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 325 given from the motion compensation circuit 25 as it is to the transform encoding circuit 29 in the intraframe encoding mode as difference data S26, and in contrast, in the interframe encoding mode. At this time, difference data S26 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 conversion encoding circuit 29.

The header data processing system SYM2 is provided with an interframe/intraframe encoding control unit 30 corresponding to the image data encoding circuit 28, and a motion compensation control unit 26.
An inter/intraframe flag Inter/In is set for specifying the encoding mode of the image data encoding circuit 28 based on the header data MDI supplied from the header data MDI and the calculation data 331 supplied from 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.
RCounLer~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)2(H>
, Σ(A-B)" (L) and Σ(A-B)" (H)
, Σ(A-FB)"(L) and Σ(A-FB)" (
H) and 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 passing through the loop filter 25B. and the upper bits, power data Σ(A-FB)z(L) and Σ(A-FB)'' (H) are current frame data S25
macroblock pixel data A and loop filter 25B
The power data Σ(A
) represents the sum of the 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 was obtained as a sign-independent value).

The filter control unit 31 controls the image data encoding circuit based on the second frame data HD2 passed from the interframe/intraframe encoding control unit 30 and the remaining amount data S32 supplied from the transmission buffer memory 32. 2
8, and transmits a filter on/off signal 334 to the loop filter 25B.
A filter flag Filter onloff representing the contents of the filter on/off signal 334 is added to the second hellada data HD2 and passed to the threshold control unit 35 as third hellada data HD3.

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 the filter on/off signal S34, the loop filter 25B is controlled 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 5 and performs frame drop when the transmission buffer memory 32 is in a state where there is a risk of overflow based on the remaining amount data S32 supplied from the transmission buffer memory 32. The third data HD3, which includes a flag instructing what should be processed, 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 324.
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 M
In addition to taking over VD (y), the filter control unit 31 performs 6 corresponding to block data Y0° to Cr.
Filter flag for bits Filter onloff
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 Y0°, Y o+, Yl. ,Y, ,C,
.

The transmission block setting circuit 34 receives six block data Y0° to C, which are sent as transform encoded data 335.
, (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 S36 in the threshold control unit 3.
Pass it to 5.

At this time, the threshold control unit 35 controls each block data Y,. ~For each CF, the power detection data S36 is compared with a predetermined threshold, and when the power detection data S36 is smaller than the threshold, the transmission of the block data is not allowed, whereas when it is larger, it is allowed. CBPN is formed and added to the third hellada data HD3 passed from the filter control unit 31 and passed to the quantization control unit 36 as the fourth hellada data HD4, and the transmission block setting circuit 34 Block data Y0°~C corresponding to
, , are sent out by the quantization circuit 37 as transmission block patterned data S37.

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, the quantization step size control signal 33B is transmitted 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 339 obtained at the output end of the quantization circuit 37 is converted into a variable length The encoding circuit is supplied on the third day.

At the same time, as shown in FIG. 4, the quantization control unit 36 generates block data Y0° to C, (third
Flag data FLAGS corresponding to each of the diagram (C))
and motion vector data MVD(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 Y, ,xC,
, motion vector data snow VD(x) and 1vD <y
) is added.

The variable length encoding circuit 38 performs variable length encoding processing on the Hellada data HD 5 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 converts block data Y0° to C, .
When performing variable length encoding, the corresponding flag data FLA
When "frame drop" or "r transmission not possible" is specified based on the GS, the block data is transferred to the transmitted image data S.
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 combines it with the transmission audio data 541 sent from the audio data generator 242 in the multiplexer 41 and sends it to the transmission line 4.
Send to 3.

The dequantization circuit 40 dequantizes the quantized image data 339 sent from the quantization circuit 37 based on the header data HD5, and then supplies the dequantized data 342 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 S44 representing the image information thus sent out as the transmission image data S40 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 344 to perform a correction operation on the pre-prediction frame data stored up to that point and stores it as new pre-prediction frame data.

Thus, according to the encoder 21A having the configuration shown in FIG. In order to synchronize with this, the header data processing system S
By doing so, pixel data can be adaptively processed as necessary by adding or deleting header data as necessary at each processing stage of the header data processing system SYM2. .

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 audio data receiving device 53 receives the transmitted audio data S51.

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 $54.

This inversely transformed encoded data 354 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.

(Then, the encoded difference data S5 is stored in the frame memory 58.
The image data transmitted based on 5 is decoded,
The decoded image data 556 is converted into an analog signal in the digital/analog conversion circuit 59 and then sent out as an output video signal VDouv via the output circuit section 60.

(G2) Frame drop processing according to the embodiment In the image information transmission system 21 shown in FIG. 1, the transmission buffer memory 32 feeds back remaining amount data S32 indicating the remaining data amount Buffer to the quantization control unit 36. The quantization step size QNT in the quantization process of the quantization circuit 37 is controlled to prevent overflow or underflow.

That is, in this embodiment, as shown in FIG. 6, the quantization circuit 37 has a table of quantization step size QNT that can vary the steps from upper limit value QNT = 31 to δ lower limit value QNT1, and quantization control The unit 36 uses the remaining data IBuffer in the transmission buffer memory 32 as a margin and a quantization size controllable range QC.
If the quantization step size QNT approaches the sum of R (that is, the allowable upper limit of the remaining data amount), the quantization step size QNT is made coarser (that is, it is changed in the direction of QNT = 31).

Therefore, the quantization circuit 37 quantizes the transform encoded data S35 with a coarse quantization step size, so that
The data amount of the quantized image data S39 is controlled to a small value, thereby reducing the remaining data amount B of the transmission buffer memory 32.
uffer continues to decrease.

On the other hand, when the remaining amount of data in the transmission buffer memory 32 decreases, the quantization control unit 36 controls the quantization circuit 37.
By changing the quantization step size QNT to a finer value (that is, between QNT = 1), the remaining data amount Bu of the transmission buffer memory 32 can be reduced.
ffer is always made to converge to the level of the target value MG (QNT = 1).

Also, the filter control unit) 31 is the transmission buffer memory 3
By inputting the remaining amount data 332 fed back by step 2, the remaining data amount Buffer of the transmission buffer memory 32 is constantly monitored and it is determined whether or not to perform frame dropping on a field by field basis.

That is, the filter control unit 31 sets an upper limit value (Margin + quantization size controllable The time tl when the range QCI?) is exceeded
(Fig. 6), it is determined that the transmission buffer memory 32 is approaching an overflow state, and the following third
Frame drop flag Drop included in flag data FLAGS of frame data HD2 of each macroblock MB corresponding to one field of image data of frame FRM2.
The fra*eflag (FIG. 5) is designated as "1" and is sent to the variable length encoding circuit 38 and dequantization circuit 40 by sequentially passing this to the header data HD3, HD4, and HD5.

The variable length encoding circuit 38 inputs header data HD.
Frame drop flag D included in flag data FLAGS of No. 5
rop frame flag is specified as "1", the quantized image data S39 input corresponding to the header data HD5 is not sent to the variable length encoding circuit, so that the transmission image data S40 is not sent. is being done.

In this way, the filter control unit 35 specifies the drop frame flag as "Drop frame flag 1" for all the macroblocks MB of the second frame FRM2, and thereby sets the variable length code for all the macroblocks MB of the frame FRM2. By controlling the transmission image data s40 not to be transmitted in the converting circuit 38, the frame FRM2 is dropped.

Therefore, in the transmission buffer memory 32 where the remaining data amount Buffer exceeds the upper limit value, data for one frame is not input, and the remaining data amount Buffer decreases by the amount of data output to the transmission path 43. do.

On the other hand, the inverse quantization circuit 4o detects the frame drop flag of the input header data HD5.
When g is specified as "1", quantized image data 339 input corresponding to the header data HD5
By not dequantizing the dequantized data 34
2 is not sent.

Therefore, all the macroblocks MB for one frame of the frame FRM2 for which frame dropping is specified in the filter control unit 31 are not outputted as dequantized data S42. The data of the frame FRM2 is also omitted in the pre-prediction frame data.

In this way, corresponding to the frame dropping process of the image data outputted via the transmission buffer memory 32, the image data of the pre-prediction frame data is also subjected to the frame dropping process.

Here, when the filter control unit 31 starts specifying frame dropping based on the remaining data amount Buffer of the transmission buffer memory 32, it continues specifying frame dropping processing on a frame-by-frame basis until the remaining data amount Buffer falls below the target remaining amount value MG. .

Therefore, the remaining data amount Buffe in the transmission buffer memory 32
Even if r falls below the upper limit at time t2 (FIG. 6), the frame dropping process continues, and at time t of the fourth frame FRM4.
3, when the value falls below the target value MC, the filter control unit 31 detects this and deletes all macroblocks MB of the frame FRM4 for which frame dropping processing is being performed at this time.
After the frame drop specification is completed, the frame drop flag of the header data corresponding to the following frame FRM5 is set.Drop frame
By specifying e flag as "0," the variable length encoding process of the quantized image data 339 is restarted in the frame FRM5.

Therefore, by inputting the transmission image data S40 of this frame FRM5 to the transmission buffer memory 32 again, the remaining data amount Buffe of the transmission buffer memory 32 is increased.
r again changes depending on the amount of input data and the amount of output data.

In this way, the filter control unit 31 controls the remaining data amount Bu
As long as ffer does not exceed the upper limit again, the frame drop flag for the header data corresponding to all macroblocks MB constituting the frame is set for each frame. op frame
By specifying e flag to "0", the transmission image data S40 is input to the transmission buffer memo U 32,
The remaining data amount Buffer changes accordingly.

Even if the data generation amount of the transmission image data S40 input at this time is rapidly increasing as in the state before executing the frame dropping process, the transmission buffer memory 32
Since the remaining data amount Buffer is reduced to the target value MO, the frame dropping process is not restarted immediately.

Therefore, it is possible to avoid a situation in which frames to be transmitted and frames that are dropped and not transmitted are repeated every frame, for example, and the transmission buffer memory 32
In the video obtained by reproducing the image data output from the , it is possible to prevent visual smoothness of movement from being impaired.

Furthermore, because the remaining data amount Buffer has been reduced to the target value MG (QNT = 1) by the frame dropping process, for example, if the amount of data generated for the transmission image data S40 in the subsequent frame FRM6 is reduced, the remaining data amount will be reduced. Since Buffer has not increased to the upper limit value, the remaining data amount Buffer can be converged to the target value MG (QNT = 1) in a shorter time.

Therefore, when a fast-moving image (i.e., an image with a large amount of transmitted image data) suddenly changes to a slow-moving image (i.e., an image with a small amount of transmitted image data), a short and fine quantization step ( QNT = 1), it is possible to immediately express a detailed image even when the movement of the image becomes slow.

Incidentally, even if a fast-moving image is expressed as a coarse image, visual deterioration will not be recognized, and in a slow-moving image, fine details can be visually recognized sensitively, so the movement of the image is slow. By being able to immediately reduce the quantization step size when this happens, it is possible to visually avoid deterioration in image quality.

Here, FIG. 7 shows the cumulative value TRM of the transmission image data amount (that is, variable length encoded data) of each frame inputted to the transmission buffer memory 32, and FDll to FD26 are 1 in each frame FRMII to FRM26, respectively.
Represents the amount of transmitted image data for one frame.

For example, when the transmission image data amount FD16 for one frame in frame FRM16 is input, the remaining data amount Buff
er is 11 Hi! E (QNT = 31), frame dropping processing starts as soon as all data of the relevant frame FRM16 is input, and the remaining data amount Buffe
r decreases relatively.

As a result, transmission image data FD17 of frame FRM17
When the remaining data amount Buffer of the transmission buffer memory 32 falls below the target value MG (QNT = 1) before the frame FRM 17 is input, the input of the transmission image data of the frame FRM 17 is restarted.

At this time, for example, the transmission image data amounts FDi7, FD18, and FD19 of the following frames FRM17, FRM1B, and FRM19 are small values, and the remaining data amount Buf fer of the transmission buffer memory 32 underflows before inputting the transmission image data of frame FRM20. Level IJ
When it falls below NDER, the transmission buffer memory 32 is prevented from underflowing by inserting stuffing bits between data before falling below the underflow level tlNDER.

(Then, in the transmission buffer memory 32, the remaining data amount Buffer is prevented from overflowing or underflowing by using dropout prevention processing or stuffing bit insertion processing, and the target value (Q!JT = 1
) is controlled to converge as much as possible.

According to the above configuration, the remaining data amount Buffer of the transmission buffer memory 32 is set to the target value MG (QNT = 1).
By performing the error prevention processing so as to converge to , it is possible to obtain an image with visually smoother movement and avoid deterioration of image quality when reproducing the output data of the transmission buffer memory 32.

(G3) Other Embodiments In the above-mentioned embodiments, a case was described in which the target value MG (QNT = 1) was used as the detection level for the end of fall protection. However, the present invention is not limited to this, and for example, Quantization size controllable range QC1 depending on the width of the amount of transmitted image data generated by fast-moving images or slow-moving images, etc.
The target value MO may be changed to another level within 2.

Further, in the above embodiment, the filter control unit 3
1, the remaining data amount Buf of the transmission buffer memory 32
Although the case has been described in which fer is detected and designated as fall protection, the present invention is not limited to this. good.

Further, in the above-described embodiment, a case has been described in which the variable length encoding circuit 38 executes the drop-off processing, but the present invention is not limited to this, and for example, the quantization circuit 37
In short, the drop prevention process may be performed in the previous stage of the transmission buffer memory 32, such as by detecting the drop protection designation of the radar data and executing the drop prevention process.

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. It can be widely applied to transmission, etc.

H Effects of the Invention As described above, according to the present invention, when the remaining data amount value of the transmission buffer memory exceeds the predetermined upper limit value, the remaining data amount value is lower than the above upper limit value. By executing the drop prevention process until the value decreases to the value, it is possible to obtain an image with visually smoother movement, and to avoid deterioration in image quality.

[Brief explanation of drawings]

1 and 2 are block diagrams showing an encoder and a decoder constituting an image information transmission system using a video signal encoding device according to the present invention, 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 Figure 6 is a diagram showing changes in the remaining amount of data in the transmission buffer memory due to failure prevention. Characteristic curve diagram, 7th
The figure is a curve diagram showing the cumulative value of transmission image data input to the transmission buffer memory, Figure 8 is a route diagram for explaining intra-frame/inter-frame encoding processing, and Figure 9 is a diagram showing a conventional image data generation device. The block diagram shown in FIG. 10 is a curve diagram showing the quantization step. 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 encoding circuit, 43...Transmission line, S32...Remaining amount data, S40...
...Transmission image data.

Claims (1)

[Claims] A transmission buffer circuit is provided, in which transmission image data subjected to high-efficiency encoding processing is temporarily stored,
In a video signal encoding device that sequentially outputs the stored transmission image data to the transmission path based on the data transmission capacity of the transmission path, when the remaining data amount value of the transmission buffer circuit exceeds a predetermined upper limit value; , the frame dropping process of the transmitted image data is executed, and the frame dropping process is terminated when the remaining data amount value of the transmission buffer circuit decreases to a predetermined target value level smaller than the above upper limit value. A video signal encoding device characterized by: