JP3461151B2 - Encoding device and method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coding apparatus and method, and is particularly suitable for application when a video signal is highly efficiently coded and converted into image data.

[0002]

2. Description of the Related Art Conventionally, in a video telephone system and a conference telephone system, a video signal, which is a moving image, is highly efficiently encoded into intra-frame coded data and inter-frame coded data to relatively limit the transmission capacity. A video signal transmission system for transmitting a moving picture video signal through a certain transmission line has been proposed (Japanese Patent Laid-Open No. 63-1183).

That is, for example, as shown in FIG. 10 (A), in the case of transmitting respective images PC1, PC2, PC3, ... Forming a moving image at time t = t ₁ , t ₂ , t ₃ ... , Intra-frame coding processing is performed by compressing image data to be transmitted by utilizing the characteristic that the video signal has a large autocorrelation over time. Is an image PC
1, PC2, PC3, etc. are subjected to compression processing such as comparing pixel data with a predetermined reference value to obtain a difference,
Thus, for each of the images PC1, PC2, PC3 ..., Image data of a compressed data amount is transmitted by utilizing the autocorrelation between pixel data in the same frame.

In addition, the inter-frame encoding process is performed by sequentially adjoining images PC1 and PC as shown in FIG. 10 (B).
2, PC2 and image data PC12 consisting of differences of pixel data between PC3 ..., PC 23 obtains a ......, which the initial image PC1 at the time t = t ₁ transmitting with intraframe coded processed image data.

Thus, the images PC1, PC2, PC3 ...
In comparison with the case of transmitting all the image data, it is possible to highly efficiently encode digital data having a remarkably small data amount and send it to the transmission path.

The encoding process of the video signal is executed in the image data generator 1 having the configuration shown in FIG.

The image data generator 1 receives the input video signal VD
Are processed in the pre-processing circuit 2 to perform one-field dropping processing and one-field line thinning processing, and then the luminance signal and the chroma signal are divided into 16 pixels (horizontal direction) × 16 pixels (vertical direction). Transmission unit block made up of data (this is called macro block) data S11
And is supplied to the image data encoding circuit 3.

The image data coding circuit 3 receives the predicted current frame data S12 formed in the prediction coding circuit 4 and obtains a difference from the macroblock data S11 to generate interframe coded data (this is the frame Inter-coded mode), or by obtaining the difference between the macroblock data S11 and the reference value data, intra-frame coded data is formed and this is used as the difference data S1.
3 to the transform coding circuit 5.

The transform coding circuit 5 is composed of a discrete cosine transform circuit, and transform coding data S14 obtained by high efficiency coding by orthogonal transforming the difference data S13 (that is, discrete cosine transform) is sent to the quantizing circuit 6. By giving the quantized image data S1
5 is sent.

Thus, the quantized image data S15 obtained from the quantization circuit 6 is subjected to high-efficiency coding again in the re-transform coding circuit 7 including a variable-length coding circuit, and then is transmitted to the transmission buffer as transmission image data S16. Memory 8
Is supplied to.

In addition to this, the quantized image data S15 is subjected to inverse quantization and inverse transform encoding processing in the predictive encoding circuit 4 to be decoded into differential data, and the post-prediction frame data is corrected by the differential data. By doing so, new pre-prediction frame data is saved, and at the same time, the pre-prediction frame data saved in the predictive coding circuit 4 is motion-compensated by the motion detection data formed on the basis of the macroblock data S11. The frame data can be formed and supplied to the image data encoding circuit 3, whereby the macroblock data S of the frame to be currently transmitted (that is, the current frame) is transmitted.
The difference between 11 and the predicted current frame data S12 is obtained as difference data S13.

In the structure of FIG. 11, when transmitting the moving image described above with reference to FIG. 10, first, FIG.
When the image data of the image PC1 is given as the macroblock data S11 at the time point t ₁ of, the image data encoding circuit 3 enters the intraframe encoding mode and converts it into the difference data S13 subjected to the intraframe encoding process. The transmission image data S16 is supplied to the encoding circuit 5, and thereby to the transmission buffer memory 8 via the quantization circuit 6 and the reconversion encoding circuit 7.

At the same time, the quantized image data S15 obtained at the output end of the quantization circuit 6 is subjected to the predictive coding process in the predictive coding circuit 4, so that the transmitted image data S16 sent to the transmission buffer memory 8 is converted. predictive previous frame data represented is held before the frame memory, followed macroblock data S11 representing an image PC2 at time t ₂ to a time when supplied to the image data coding circuit 3, is the motion compensated prediction current frame data S12 It is supplied to the image data encoding circuit 3.

Thus, at time t = t ₂ , the image data coding circuit 3 supplies the difference data S13 subjected to the inter-frame coding process to the transform coding circuit 5, whereby the difference data representing the change of the image between the frames. Is supplied to the transmission buffer memory 8 as the transmission image data S16, and the quantized image data S15 is supplied to the prediction encoding circuit 4 to form and store the pre-prediction frame data in the prediction encoding circuit 4. .

By repeating the same operation thereafter, while the image data encoding circuit 3 is executing the interframe encoding process, only the difference data representing the change of the image between the previous frame and the current frame is obtained. The data will be sequentially sent to the transmission buffer memory 8.

The transmission buffer memory 8 stores the transmission image data S16 thus sent out, and the accumulated transmission image data S16 is sequentially transmitted at a predetermined data transmission rate determined by the transmission capacity of the transmission line 9. D
_It is extracted as _TRANS and transmitted to the transmission line 9.

At the same time, the transmission buffer memory 8 detects the amount of remaining data and feeds back the remaining amount data S17 which changes according to the remaining amount of data to the quantizing circuit 6 to respond to the remaining amount data S17. By controlling the quantization step size, the amount of data generated as the transmission image data S16 is adjusted so that an appropriate amount of data (data amount that does not cause overflow or underflow) in the transmission buffer memory 8 can be obtained. Is being maintained.

Incidentally, when the remaining amount of data in the transmission buffer memory 8 has increased to the allowable upper limit, the quantization step STPS (twelfth) of the quantization circuit 6 is performed by the remaining amount data S17.
By increasing the step size in the figure), the quantization circuit 6 performs coarse quantization to reduce the data amount of the transmission image data S16.

On the contrary, when the remaining amount of data in the transmission buffer memory 8 is reduced to the allowable lower limit value, the remaining amount data S17 has a small step size of the quantization step STPS of the quantization circuit 6. In this way, the quantization circuit 6 is caused to execute fine quantization, thereby increasing the data generation amount of the transmission image data S16.

[0020]

As described above, in the conventional image data generating apparatus 1, the data transmission rate of the transmission data D _TRANS is significant while matching the transmission condition in which the data transmission rate is limited based on the transmission capacity of the transmission line 9. As a means for transmitting image information, the generated image data is stored in the transmission buffer memory 8 so that the image data of a data amount corresponding to the transmission capacity of the constant transmission path 9 is equal to the transmission capacity of the constant transmission path 9. However, if the signal value represented by the image data to be actually transmitted is large, if the signal value is quantized as it is, the amount of data stored in the transmission buffer memory 8 is large. There is a risk that the amount will become excessive, and it is desirable to be able to compress to a practically appropriate amount of data.

The present invention has been made in consideration of the above points, and it is an object of the present invention to generate quantized image data of an appropriate data amount according to image data to be quantized.

[0022]

In order to solve the above problems, in the present invention, the discrete cosine transform coefficient data obtained by the discrete cosine transform of the difference data between the current frame data and the predicted current frame data is quantized. To obtain quantized discrete cosine transform coefficient data, and to generate pre-prediction frame data by performing inverse quantization processing and inverse discrete cosine transform processing on the quantized discrete cosine transform coefficient data,
The predicted current frame data is generated by detecting the motion vector of the current frame data for this pre-prediction frame data and compensating the motion of the current frame data, and the first data which is the image data of the macro block of the current frame is generated. , A change in the contents of the first and second data is evaluated based on the difference between the detected motion vector and the second data which is the image data of the macroblock of the predicted current frame. By controlling the quantization step during the quantization processing in the quantization means according to the evaluation data indicating You can

[0023]

[0024]

[0025]

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments in which the present invention is applied to a videophone will be described below in detail with reference to the drawings.

(G1) Overall Structure of Image Information Transmission System In FIGS. 1 and 2, the image information transmission system 21 is composed of an encoder 21A and a decoder 21B, and the encoder 21A receives the input video signal VD _IN from the input circuit section 22. In the analog / digital conversion circuit 23 after pre-processing in the transmission unit block data consisting of pixel data of 16 × 16 pixels, that is, the macro block MB.
The input image data S21 consisting of the pixel data is sent to the pixel data processing system SYM1, and at the timing when the pixel data is processed in units of the macroblock MB in each processing stage of the pixel data processing system SYM1, the data is processed. Corresponding processing information data is sequentially transmitted through the header data processing system SYM2, and thus the pixel data and the header data are processed by the pipeline method in the pixel data processing system SYM1 and the header data processing system SYM2, respectively. go.

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

First, one frame image data FRM is divided into 2 (horizontal direction) × 6 (vertical direction) block groups GOB as shown in FIG. 3A, and each block group GOB is divided into As shown in FIG. 3 (B), 11 (horizontal direction) × 3 (vertical direction) macroblocks MB are included, and each macroblock MB is the third.
Luminance signal data Y for 16 × 16 pixels as shown in FIG.
_{00 to} Y ₁₁ (each consisting of luminance signal data for 8 × 8 pixels) and luminance signal data Y _{00 to} Y _{11 including} color signal data C _b and C _r consisting of color signal data corresponding to all pixel data. Become.

Thus, the input image data S21 sent out for each macro block MB is given to the motion compensation circuit 25, and the motion compensation circuit 25 is given from the motion compensation control unit 26 provided for the header data processing system SYM2. In response to the motion detection control signal S22, the pre-prediction frame data S23 in the pre-prediction frame memory 27 and the input image data S21 are compared with each other to calculate the motion vector data MVD (x).
And MVD (y) are detected and the motion compensation control unit 26
Of the motion vector data MVD (x) and MVD (y) with respect to the pre-prediction frame data S23 in the motion compensation circuit main body 25A. The predicted current frame data S24 is formed and supplied to the image data encoding circuit 28 together with the current frame data S25 which is the input image data S21 currently to be processed.

Here, the motion compensation control unit 26 has a fourth
As shown in the figure, for each macroblock currently being processed as the first header data HD1, the transmission frame number data TR C indicating the transmission order of the frame image data FRM.
ounter and block group number data GOB addres representing the block group GOB (FIG. 3 (A))
By adding s and the macroblock number data MB address representing the macroblock MB among them, the macroblock MB sequentially transmitted to each processing stage of the pixel data processing system SYM1 is displayed. Flag data FLAGS representing the processing or processing format of the processing target macroblock MB, motion vector data MVD (x) and MVD (y) of the macroblock MB, and difference data Σ | AB | And form.

As shown in FIG. 5, the flag data FLAGS is designed to have a flag for 1 word (16 bits) at the maximum, and the 0th bit is set in the motion compensation mode for the macro block MB to be processed. The motion compensation control flag MC on / off indicating whether or not to process is set.

The first bit of the flag data FLAGS is an inter-frame indicating whether the macro block MB to be processed should be processed in the inter-frame coding mode or in the intra-frame coding mode. / Intra-frame flag Inter / Intra is set.

A filter flag Filter on / off indicating whether to use the loop filter 25B of the motion compensation circuit 25 is set in the second bit of the flag data FLAGS.

Further, the third bit of the flag data FLAGS is a transmission flag indicating whether or not the block data Y _{00 to} C _r (FIG. 3 (C)) contained in the macro block to be processed should be transmitted. Coded / Not-coded can be set.

Further, a drop frame flag Drop frame flag indicating whether or not to drop the macro block MB to be processed can be set in the fourth bit of the flag data FLAGS.

Further, the fifth bit of the flag data FLAGS has a forced refresh flag Refresh on indicating whether or not the macro block MB to be processed is forcibly refreshed.
You can set / off.

The macroblock power evaluation flag MBP appreciate can be set in the sixth bit of the flag data FLAGS.

The difference data .SIGMA. | AB | is the macroblock data A of the current frame data S25 to be currently processed and the macroblock data B compensated by the motion vector for detection of the pre-prediction frame data S23. It represents the minimum value of the differences, so that the motion vector detected can be evaluated.

In the intra-frame coding mode, the image data coding circuit 28 supplies the current frame data S25 given from the motion compensation circuit 25 to the transform coding circuit 29 as the difference data S26 as it is, and the inter-frame coding in response thereto. In the encoding mode, the difference data S26, which is the difference between the pixel data of the current frame data S25 and the pixel data of the predicted current frame data S24, is supplied to the conversion encoding circuit 29.

The header data processing system SYM2 is provided with an interframe / intraframe coding control unit 30 corresponding to the image data coding circuit 28, and the header data HD1 and the image data supplied from the motion compensation control unit 26 are supplied. Operation data S3 supplied from the encoding circuit 28
On the basis of 1, the inter-frame / in-frame flag Inte for designating the encoding mode of the image data encoding circuit 28.
r / Intra (Fig. 5) and a filter flag Filt for controlling the operation of the loop filter 25B of the motion compensation circuit 25
er on / off (FIG. 5) is calculated and sent to the filter control unit 31 as the second header data HD2.

As shown in FIG. 4, the second header data HD2 takes over the transmission frame number data TR Counter to the difference data Σ | AB | which constitutes the header data HD1 as they are, and at the same time, in the filter control unit 31. Interframe / intraframe coding mode switching signal S33
And power data Σ (A) ² (L) and Σ (A) ² (H) necessary to form the filter on / off signal S34,
Σ (A−B) ² (L) and Σ (A−B) ² (H), Σ (A−
FB) ² (L) and Σ (A-FB) ² (H), Σ (A) are added in the inter-frame / intra-frame coding control unit 30.

Here, the power data Σ (A) ² (L) and Σ (A) ² (H) represent the lower and upper bits of the sum of squares of the macroblock pixel data A of the current frame data S25, and the power Data Σ (A−B) ² (L) and Σ (A−
B) ² (H) is 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. It represents the lower bit and the upper bit, and the power data Σ (A-FB) ² (L) and Σ (A-FB) ² (H) are formed via the macroblock pixel data A of the current frame data S25 and the loop filter 25B. The lower and upper bits of the sum of squares of the difference A-FB from the macroblock pixel data FB of the predicted current frame data S24 are represented, and the power data Σ (A) is the macroblock pixel data A of the current frame data S25. Represents a sum, and expresses the amount of data as a power value in order to evaluate the size of each data to be processed (sum of squares is independent of sign). Is obtained) as a.

The filter control unit 31 receives the second frame passed from the interframe / intraframe coding control unit 30.
On the basis of the header data HD2 and the remaining amount data S32 supplied from the transmission buffer memory 32, the inter-frame / intra-frame encoding mode switching signal S33 is sent to the image data encoding circuit 28 and the loop filter 25B, a filter on / off signal S34 is transmitted, and a filter flag Filter on / off representing the content of the filter on / off signal S34 is added to the second header data HD2 to obtain third header data HD3. It is passed to the threshold control unit 35.

Here, the filter control unit 31 is the first
In addition, when the amount of transmission data when the inter-frame encoding process is performed is larger than the amount of transmission data when the intra-frame encoding process is performed, the image data encoding circuit 28 is controlled to the intra-frame encoding mode.

Secondly, the filter control unit 31 is
When the difference value of the prediction current frame data S24 which has not been subjected to the processing is smaller than the prediction current frame data S24 which has been processed by the loop filter 25B in the state where the processing is performed in the inter-frame coding mode, the filter is turned on. The loop filter 25B is controlled so as not to perform the filtering operation by the / OFF signal S34.

In addition, the filter control unit 31 thirdly
When the forced refresh mode is entered, the image data coding circuit 28 is switched to the intraframe coding mode by the interframe / intraframe coding mode switching signal S33.

Further, the filter control unit 31 has a fourth
In addition, when a state in which the transmission buffer memory 32 may overflow based on the remaining amount data S32 supplied from the transmission buffer memory 32 is detected, a flag for instructing that frame drop processing should be performed by detecting this is set. The included third header data HD3 is sent to the threshold control unit 35.

Thus, the image data encoding circuit 28 supplies the difference data S26 obtained by encoding in the mode in which the difference between the current frame data S25 and the predicted current frame data S24 is minimized to the transform encoding circuit 29.

As shown in FIG. 4, the third header data HD3 includes the header data HD2 to the transmission frame number data TR Counter to the motion vector data MVD (x) and MVD (y).
And the filter control unit 31 adds a 6-bit filter flag Filter on / off corresponding to the block data Y _{00 to} C _r .

The transform coding circuit 29 is a discrete cosine transform circuit, and the coefficient values after the discrete cosine transform are divided into six blocks Y ₀₀ , Y ₀₁ , Y ₁₀ , Y ₁₁ , and C.
_It is sent to the transmission block setting circuit 34 as conversion coded data S35 obtained by zigzag scanning for each _b and C _r .

The transmission block setting circuit 34, for each of the six block data Y _{00 to} C _r (FIG. 3 (C)) sent out as the transform-coded data S35, the coefficient data at the beginning to 2 of the coefficient data n. The sum of products is calculated and the calculation result is passed to the threshold control unit 35 as the power detection data S36.

At this time, the threshold control unit 35 sets the power detection data S for each block data Y _{00 to} C _r.
36 is compared with a predetermined threshold, and when the power detection data S36 is smaller than the threshold, transmission of the block data is not permitted, and when it is larger, transmission permission flag data CB for 6 bits is transmitted.
A PN is formed and this is added to the third header data HD3 passed from the filter control unit 31 and passed as the fourth header data HD4 to the quantization control unit 36, and at the same time, from the transmission block setting circuit 34 to the corresponding block. The data Y _{00 to} C _r are sent to the quantizing circuit 37 as transmission block patterned data S37.

Here, as shown in FIG. 4, the fourth header data HD4 inherits the transmission frame number data TR Counter to the filter flag Filter on / off of the header data HD3 as they are and the threshold control unit 35.
In, a 6-bit transmission permission flag CBPN generated corresponding to the blocks Y _{00 to} C _r is added.

The quantization control unit 36 receives the fourth header data HD4 passed from the threshold control unit 35.
And the remaining amount data S32 sent from the transmission buffer memory 32, the quantization step size control signal S38 is given to the quantization circuit 37 by executing the quantization step size determination processing routine RT0 shown in FIG. ,
As a result, the quantizing circuit 37 is quantized by the quantizing step size suitable for the data included in the macroblock MB, and as a result, the quantized image data S39 obtained at the output end of the quantizing circuit 37 is converted into the variable length coding circuit. 38.

At the same time, the quantization control unit 36, as shown in FIG. 4, sets the block data Y ₀₀ as the fifth header data HD5 based on the header data HD4.
˜C _r (FIG. 3 (C)), which is divided into flag data FLAGS and motion vector data MVD (x) and MVD (y), respectively, which are arranged in series to form a variable length code. It is passed to the quantization circuit 38 and the dequantization circuit 40.

Here, the header data HD5 is, as shown in FIG. 4, the transmission frame number data TR Counter to the macroblock number data MB add of the header data HD4.
Quantization control unit 3 while taking over ress as it is
Quantization size data QNT in 6, the flag data FLAGS for the block data Y ₀₀ -C _r, adds the motion vector data MVD (x) and MVD (y).

The variable length coding circuit 38 uses the header data HD
5 and the quantized image data S39 are subjected to variable length coding to form transmission image data S40, which is supplied to the transmission buffer memory 32.

The variable length coding circuit 38 uses the block data Y.
The ₀₀ -C _r when variable length coding, the corresponding flag data FLAGS "frame dropping" based on, or when the "not sent" is specified, without sending the block data as a transmission image data S40 Processing such as discarding.

The transmission buffer memory 32 stores the transmission image data S40, reads it out at a predetermined transmission speed, and synthesizes it with the transmission voice data S41 sent from the voice data generator 42 in the multiplexer 41 to transmit the transmission line 43. Send to.

The inverse quantization circuit 40 converts the quantized image data S39 sent from the quantization circuit 37 into the header data HD5.
Dequantized based on the dequantized data S42
Is supplied to the inverse transform coding circuit 43 to be converted into the inverse transform coded data S43 and then supplied to the decoder circuit 44, thus predicting the encoded difference data S44 representing the image information transmitted as the transmission image data S40. It is supplied to the previous frame memory 27.

At this time, the pre-prediction frame memory 27 uses the encoded difference data S44 to perform a correction operation on the pre-prediction frame data that has been saved until then and saves it as new pre-prediction frame data.

Thus, the encoder 21A having the configuration shown in FIG.
According to this, while the pixel data is pipeline processed in macroblock units in the pixel data processing system SYM based on the header information supplied from the header data processing system SYM2, the header data is synchronized with this. The header data processing system SYM is provided by passing the header data in the processing system SYM2.
Pixel data can be adaptively processed as needed by adding or deleting header data in each processing stage of No. 2 as necessary.

As shown in FIG. 2, the decoder 21B receives the transmission data transmitted from the encoder 21A via the transmission path 43 in the transmission buffer memory 52 via the demultiplexer 51 and outputs the transmission voice data S51 as voice. The data receiving device 53 receives it.

The image data received in the transmission buffer memory 52 is received image data S5 in the variable length inverse conversion circuit 54.
2 and header data HD11, which are inversely quantized by the inverse quantization circuit 55 into inversely quantized data S53 and then inversely transformed into inversely transformed encoded data S54 by the inverse transform encoding circuit 56. To be done.

This inverse transform encoded data S54 is given to the decoder circuit 57 together with the header data HD12 formed in the inverse quantization circuit 55, and the encoded difference data S5 is obtained.
5 is stored in the frame memory 58.

Thus, the image data transmitted to the frame memory 58 based on the encoded difference data S55 is decoded, and the decoded image data S56 is converted into an analog signal in the digital / analog conversion circuit 59. It is sent out as an output video signal VD _OUT via the output circuit section 60.

(G2) Quantization step size determination processing The quantization control unit 36 executes the quantization step size determination processing routine RT0 shown in FIG. 6 for each macro block MB so that the macro block MB currently to be processed is By selecting a quantization step size QNT that is suitable for the format of the image data that it has (this is called a macroblock type) and supplying it to the quantization circuit 37 as a quantization step size control signal S38,
The quantizing circuit 37 is controlled so as not to cause image quality disturbance that may occur depending on the macro block type.

In the case of this embodiment, the quantizing circuit 37 uses an upper limit value as the quantizing step size QNT, as shown in FIG.
The steps from QNT = 31 to the lower limit value QNT = 1 are made variable, and the quantization control unit 36 determines that the data remaining amount Buffer of the transmission buffer memory 32 is the quantization step size QN.
Adaptive control of the quantization step size QNT according to the macro block type so that the value is equivalent to the variable control range of T, that is, the quantization size controllable range QCR. To do.

(G2-1) Processing when the remaining amount of data is excessive, that is, the quantization control unit 36 enters the quantization step size determination processing routine RT0 shown in FIG. 6, and the remaining amount of the transmission buffer memory 32 in step SP1. Data Bu
ffer is margin Margine and quantization size controllable range QCR
It is judged whether it is greater than the sum of and.

If an affirmative result is obtained here, this means that the data remaining amount Buffer of the transmission buffer memory 32 exceeds the upper limit value. At this time, the quantum controllable unit 36 moves to step SP2 and the quantum controllable unit 36 moves to the quantum level. Step size QN
After supplying the quantization step size control signal S38 for setting T to the maximum value, that is, QNT = 31, to the quantization circuit 37, the process proceeds to step SP3, and the currently set quantization step size QNT is set to the previous frame quantization step. Size PQ
Save as NT.

Thus, the quantization control unit 36 terminates the quantization step size determination processing routine RT0 at step SP4, whereby the quantization circuit 37 executes the quantization of the transform coded data S35 with the coarsest quantization step size. To do.

As a result, the data amount of the quantized image data S39 generated from the quantization circuit 37 is controlled to the smallest value, and the remaining data amount Buffer of the transmission buffer memory 32 decreases.

This operation is repeatedly executed while a positive result is obtained in step SP1, and as a result, the remaining amount data in the transmission buffer memory 32 becomes a value smaller than the sum of the margin Margine and the quantization size controllable range QCR QCR + Margine. .

(G2-2) Processing in intra-frame coding mode In such a state, the quantization control unit 36 obtains a negative result in step SP1, moves to step SP5, and moves to macro block type Macro Bloc.
Block where k Type is an intra-frame coded block and is not a forced refresh block not refresh bloc
Judge whether k or not.

Here, the macro block type Macro Block
As shown in FIG. 8, Type is represented by the 2nd bit, 1st bit, and 0th bit of the flag data FLAGS included in the header data HD4 passed from the threshold control unit 35 to the quantization control unit 36. , When these bits are “010”, the macroblock type is intra-frame coding type Intra, when they are “000”, it is inter-frame coding type Inter, and when they are “001”, the filter-free motion compensation type MC- is not filtered, and "1
When it is "01", it becomes a motion compensation type MC-filtered using a filter.

Therefore, when a positive result is obtained in step SP5, this means that the second flag data FLAGS
It indicates that the 1st and 0th bits are “000” and the forced refresh flag refresh of the 4th bit is in the state of logic “0”.

By the way, such a state means that the current frame changes drastically with respect to the previous frame so that the macroblock type requires intra-filter coding, and the forced refresh mode is not currently designated. It means that it is under such conditions.

Under such a condition, the quantization circuit 3
7, the quantization image data S3 generated from the quantization circuit 37 is quantized with a fine quantization step size.
It can be said that the data amount of 9 becomes a very large value, and eventually the buffer memory 32 is about to overflow.

At this time, the quantization control unit 36 moves to step SP6 and sets the quantization step size QNT to the upper limit value QN.
By setting T = 31, the processing for suppressing the data amount of the quantized data S39 generated from the quantization circuit 37 is executed, and as a result, the occurrence of the overflow of the transmission buffer memory 32 is avoided. .

On the other hand, when a negative result is obtained in step SP5, this means that the type of the macroblock to be processed is not the intra-frame coding type Intra.
Or, even an intra-frame coding type Intra indicates that it is a result of the forced refresh, and at this time, the quantization control unit 36 jumps without performing the process of step SP6.

(G2-3) Processing in forced refresh mode Next, the quantization control unit 36 determines in step SP7 that the type of the macroblock to be processed is forced refresh type.
Judge whether it is a refresh block or not.

When an affirmative result is obtained here, this means that the forced refresh should be designated, and at this time, the quantization control unit 36 performs the step S.
Go to P8, set the previous frame quantization step size PQNT used in the quantization process of the previous frame as the quantization step size QNT, and if the forced refresh process is to be executed by this, the previous frame is set. Quantization is executed with the same quantization step size as.

In this way, when the forced refresh process is executed, it is possible to prevent the image quality from being changed so that the forced refresh process does not hinder the practical use.

Incidentally, the forced refresh is executed at a predetermined cycle and independently of the content of the image, so that the value of the quantization step size is smaller than that of the previous frame even though the content of the image does not change. When there is a change, the change is often annoying.

On the other hand, if the value of the quantization step size is not changed when the forced refresh is designated, it is possible to prevent an annoying change in the image during the refresh.

The same effect as in the above case can be obtained by selecting a slightly smaller value instead of selecting the same value for the quantization step size.

When forced refresh is designated in a state where there is no change in the image, if the quantization step size is increased, this will deteriorate the image quality of the restored image. By making the size a little smaller, the image quality of the restored image can be improved a little, so that it can be practically not perceived by the human eye as a change in the image.

On the other hand, when a negative result is obtained in step SP7, this means that the forced refresh is not currently designated. At this time, the quantization control unit 36 does not perform the process in step SP8. Jump this to.

(G2-4) Processing when the Power of Differential Data is Large Next, in step SP9, the quantization control unit 36 determines that the macroblock type is the interframe coding type Inter and the macroblock power MBP is a predetermined threshold value. Judge whether it is larger than Threshold.

Here, the macro block power MBP is

[0092]

[Equation 1]

As defined by step SP
If a positive result is obtained in 9, this means that the image data of the macroblock MB in question, that is, the macroblock power MBP of the difference data is large, so that the restored image is quantized with a coarser quantization step size and transmitted. This means that the image quality is in a state where there is no effect such that the image quality is extremely deteriorated.

Therefore, in the quantization control unit 36, the macroblocks satisfying such a condition are converted into the transform coding circuit 29.
When discrete cosine conversion is performed in,
This is confirmed in step SP9, and step SP1
Moving to 0, the quantization step size QNT is set to the coarsest value, that is, the upper limit value 31.

On the other hand, the transform coded data S of the macroblock whose macroblock power MBP is not so large.
When 35 is transmitted, the quantization control unit 36 jumps this so as not to perform the processing of step SP10.

The macroblock power MBP represented by the equation (1) is the weight of each macroblock based on the discrete cosine transform coefficient C _oeff (i) obtained as a result of the discrete cosine transform processing in the transform coding circuit 29. , The weight of the discrete cosine transform coefficient represents the strength of the transmission signal obtained by the discrete cosine transform.Therefore, the fact that the macroblock power MBP is large means that the signal is transmitted as a signal transmission means. Since the signal strength is large, it means that the transmission information can be correctly reproduced without being affected by the external noise on the receiving side even if the signal is slightly compressed and transmitted.

Therefore, in such a case, the quantization control unit 36 compresses the data amount of the quantized data S39 generated in the quantization circuit 37 by changing the quantization step size QNT to a large value, and thereby the transmission line 43.
To reduce the burden on

Incidentally, the discrete cosine transform circuit constituting the transform coding circuit 29 has the following equation:

[0099]

[Equation 2]

The discrete cosine inverse transform circuit, which forms the inverse transform coding circuit 56 while executing the discrete cosine transform by

[0101]

[Equation 3]

The discrete cosine inverse transform is executed by. Here, x and y represent the coordinates of the pixel in the macroblock (the coordinates of the upper left corner are (0, 0)), and u and v represent the coordinates of the coefficient at the time of the discrete cosine transform.

When u and v = 0,

[0104]

[Equation 4]

In other cases,

[0106]

[Equation 5]

It becomes as follows.

The conversion of equations (2) and (3) is actually X
Where C is the image data matrix in the macroblock and C is the conversion matrix at the time of the discrete cosine transform, the transform coding circuit 29 first horizontally transforms the image data matrix X to obtain the transformed image data matrix XC ^-1 . After that, vertical conversion processing is performed again to obtain a converted image data matrix C (X) C ^-1 .

Transformed image data matrix C thus obtained
(X) C ⁻¹ is the coefficient C as shown in FIG.
_oeff (1), _Coeff (2), _Coeff (3) ... C
_oeff (64) can be represented as a conversion coefficient matrix consisting of an 8 × 8 matrix, and each coefficient C _oeff (i) of the conversion coefficient matrix
(I = 1 to 64) are read out from the conversion matrix while scanning in the order of i = 1, 2, 3 ... 64 as time passes.

Thus, the image data of one macroblock is converted into the conversion coefficient C _{oe ff} (i) (i = 1 to 1) which forms the conversion matrix.
64), which is supplied to the quantization circuit 37 as transmission data arranged in time series.

Thus, the transform coefficient data string C _oeff (1), C _oeff (2) ... C supplied to the quantization circuit 37.
_oeff (64) represents the information to be transmitted and also represents the strength of the signal to be transmitted. Therefore, as represented by the equation (1), the conversion coefficient data string C _oeff I = included in (i) (i = 1, 2 ... 64)
The square of the transform coefficient data from 1 to n is a value obtained by cumulatively adding the strength of the signal to be transmitted so that the influences in the horizontal direction and the vertical direction are equal, and in the end, the formula (1) is used as a macroblock. It is defined as a power MBP.

When the transform coefficient matrix as shown in FIG. 9 is obtained by _{actually performing the} discrete cosine transform on the image data, the transform coefficient C _oeff (i) at the upper left corner, that is, the low-order transform coefficient has power. In contrast, the conversion coefficient in the lower right corner, that is, the higher-order conversion coefficient, tends not to generate significant information, and thus the transmission data can be compressed by the discrete cosine conversion.

Therefore, when it is confirmed in step SP9 in FIG. 6 that the macro block type Macro Block Type is the inter-frame coding type Inter, the macro block power MBP obtained based on the equation (1) is a predetermined threshold value. If it can be confirmed that it is larger than the Threshold, this means that the value of the difference data in the macroblock MB is sufficiently large, and thus coarse quantization may be performed. Therefore, if the quantization step size QNT is selected as the upper limit value in step SP10 according to such a judgment, the difference data can be transmitted with a relatively small data amount.

(G2-5) Processing in the interframe coding mode In step SP11 of FIG. 6, the quantization control unit 36 determines that the macroblock type Macro Block Type is the interframe coding type Inter and the macroblock power is
When it is confirmed that MBP is smaller than the predetermined threshold value Threshold, the process proceeds to step SP12, where the quantization step size QNT is set to 1/2 of the previous frame quantization step size PQNT used in the previous frame, and then the step In SP13, it is determined whether or not the value of the set quantization step size QNT is smaller than the lower limit value 1, and when it is smaller, the quantization step size QNT is reset to the lower limit value 1 in step SP14 and is not smaller than 1. Occasionally, the value is set as the quantization step size QNT without resetting.

Here, the macroblock power MBP is (1)
Since the strength of the differential data signal of the image data of the macroblock is expressed as described above with respect to the equation, when the positive result is obtained in step SP11, the difference is small, and therefore the content of the image is the image of the previous frame. It shows that the change is small compared to.

When such image data is obtained, the image to be transmitted at present is in a state in which the image of the previous frame is only partially modified without being significantly changed. It means that.

Therefore, in step SP12, the quantization control unit 36 finely divides the quantization step size PQNT into 1/2 based on the quantization processing result of the previous frame and sets it as the quantization step size QNT of the current frame. By doing so, the quantization step size can be made smaller for the current frame in which the motion is less than that in the previous frame, so that the optimum quantization step size can be set.

Since such a quantization step size reduction process is repeatedly executed by the quantization control unit 36 in steps SP11 and SP12 as long as an image with less motion continues, eventually, when an image with less motion is continuously transmitted. Will allow the quantization step size to converge to a value that accommodates this.

In doing so, steps SP13 and S
Since the quantization step size QNT is not made smaller than the lower limit value 1 in P14, the quantization control unit 36 eventually converges the quantization step size QNT to the lower limit value when transmitting an image with little motion. With this, the quantization process can be performed stably.

On the other hand, when a negative result is obtained in step SP11, the quantization control unit 36 judges that the change of the image to be transmitted at present is large and skips the processing of steps SP12, SP13 and SP14. Jump this.

(G2-6) Operation of Quantization Control Unit 36 In FIG. 6, firstly, when the remaining amount data Buffer of the transmission buffer memory 32 exceeds the upper limit value (QCF + Margin),
The quantization control unit 36 detects this in step SP1 and sets the quantization step size QNT of the quantization circuit 37 to the upper limit value 31 in step SP2, thereby reducing the data remaining amount data buffer of the transmission buffer memory 32. As a result, control is performed so as to maintain the state below the upper limit value.

Secondly, in this state, when the block data which the macro block type Macro Block Type is the intra-frame coding type and is not the forced refresh block is given to the quantization circuit 37, the quantization control unit 36 steps this. Confirm at SP5 and step SP6
In the transmission buffer memory 32 by setting the quantization step size QNT of the quantization circuit 37 to the upper limit value 31.
Control not to overflow.

In such an operation mode, the quantization control unit 36 obtains a negative result in each of steps SP7, SP9, and SP11.
After the quantization step size set in P6 is set as the previous frame quantization step size PQNT in step SP3, the processing procedure ends.

Thirdly, when the quantizing circuit 37 is supplied with data having the macro block type of the forced refresh block type, the quantizing control unit 36 causes the quantizing step size determining processing routine RT0 to execute the step SP.
This is determined by the loop of 1-SP5-SP7, and in step SP8 the quantization step size QNT of the quantization circuit 37 is set as the previous frame quantization step size PQNT.
Is set so that the image quality of the image to be transmitted when the forced refresh mode is entered is not changed from the image of the previous frame, thereby preventing an annoying change in the image quality during forced refresh.

At this time, the quantization control unit 36 sets the quantization step size QNT set in step SP8 as the previous frame quantization step size PQNT in step SP3 because negative results are obtained in steps SP9 and SP11. The process ends.

Fourthly, when the image data of the macroblock having a large macroblock power MBP is supplied to the quantizing circuit 37, the quantizing control unit 36 causes the quantizing step size determining processing routine RT0 to execute the step SP1.
This is confirmed by the loop of -SP5-SP7-SP9, and the quantization step size QNT of the quantization circuit 37 is set to the upper limit value 31 in step SP10.
The amount of data generated in the quantization circuit 37 can be suppressed to a small value, and as a result, image data can be transmitted more efficiently.

At this time, the quantization control unit 36 obtains a negative result in step SP11 after the above processing is completed, so that the quantization step size QNT set in step SP10 in step SP3 is set to the previous frame quantization step size PQNT. Then, the processing routine is ended.

Fifth, when the quantization circuit 37 is supplied with the macroblock data of the inter-frame coding type and the macroblock power MBP is small, the quantization control unit 36 determines this by the step of the quantization step size determination processing routine RT0. It is confirmed by the loop of SP1-SP5-SP7-SP9-SP11, and at step SP12, the value of 1/2 of the previous frame quantization step size PQNT is set as the quantization step size QNT, so that the quantization step size is the lower limit value. Converge to 1.

Thus, the optimum quantization step size can be set by applying it to the macroblock power MBP.

(G3) Other Embodiments (1) The case where the quantization step size QNT is set to the upper limit value 31 in steps SP6 and SP10 in FIG. 6 has been described, but the upper limit is set as the quantization step size QNT to be set. Not limited to the values, other values may be selected, and the point is to select a coarse quantization value having a size capable of performing coarse quantization.

(2) Steps SP9 and SP11 in FIG.
In the above, when judging the size of the macroblock power MBP, the case where the same threshold value Threshold was selected was described, but instead of this, even if a different value is selected, the same effect as the above case can be obtained. Obtainable.

(3) In step SP12 of FIG. 6, when the quantization step size QNT is obtained from the previous frame quantization step size PQNT, the half of the value is set. Is not limited to 1/2, but may be changed to another value as necessary, the point is to select a quantization step size reduced by a predetermined ratio with respect to the previous frame quantization step size. .

(4) Steps SP13 and SP1 in FIG.
Although the case where the quantization step size QNT is made to converge to the lower limit value 1 in 4 has been described, the value to be converged is not limited to the lower limit value, and other values may be selected as necessary.

[0134]

As described above, according to the present invention, the evaluation data is generated based on the difference between the image data of the macroblock of the current frame and the image data of the macroblock of the predicted current frame, and based on the evaluation data. By controlling the quantization step supplied to the quantization means,
It is possible to always generate an appropriate amount of quantized image data.

[Brief description of drawings]

FIG. 1 is a block diagram showing an encoder constituting an image information transmission system to which a video signal encoding method according to the present invention is applied.

FIG. 2 is a block diagram showing a decoder constituting an image information transmission system to which a video signal coding method according to the present invention is applied.

FIG. 3 is a schematic diagram showing the structure of frame image data.

FIG. 4 is a block diagram showing a header data processing system of FIG.

5 is a schematic diagram showing a configuration of flag data of FIG.

6 is a flowchart showing a quantization step size determination processing routine of the quantization control unit 36 in FIG.

FIG. 7 is a curve diagram showing changes in the remaining amount data of the transmission buffer memory 32 of FIG.

FIG. 8 is a chart showing types of macroblock types.

FIG. 9 is a chart showing a transform coefficient matrix.

FIG. 10 is a schematic diagram for explaining intraframe / interframe encoding processing.

FIG. 11 is a block diagram showing a conventional image data generator.

FIG. 12 is a curve diagram showing the quantization step.

[Description of Codes] 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 coding circuit, 29 ... Transformation coding circuit, 30 ... Inter-frame / intra-frame coding control unit, 31 ... Filter control Unit, 32 ... Transmission buffer memory, 34 ... Transmission block setting circuit, 3
5 ... Threshold control unit, 36 ... Quantization control unit, 37 ... Quantization circuit, 38 ... Variable length coding circuit.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 7/32 H03M 7/30 H04N 7/14

Claims (2)

(57) [Claims] 1. A coding device for coding image data.
hand,The current frame data of the above image data and the predicted current frame data
Image data encoding means for outputting difference data of the data, Difference data above Against the discrete cosine transform
Discrete cosine transform by applying processing
Discrete cosine transform means for generating coefficient data
When, Based on the specified quantization step,
Quantize tocosine transform coefficient data
By the quantized discrete cosine transform coefficient
Quantizing means for generating data,For the above quantized discrete cosine transform coefficient data,
Then, the inverse quantization process and the inverse discrete cosine transform process are performed.
To generate pre-prediction frame data
Pre-prediction frame data generation means, The motion of the pre-prediction frame data and the current frame data
By detecting the vector
Motion compensation of the current frame data
The predicted current frame that generates the predicted current frame data.
Data generation means, Up Control means for controlling the quantization processing in the quantization means
With The control means controls the image data of the macroblock of the current frame.
DataAnd the predicted current frame data
Prediction current when using the motion vector detected by the generation means
The second data which is the image data of the macroblock of the frame.
DataBased on the difference betweenThe first data and the second
Changes in the data content ofGenerate evaluation data and
Quantum supplied to the quantizing means based on the evaluation data
An encoding device for controlling an encoding step. 2. A coding method for coding image data.
hand,By the image data encoding means, the current frame of the image data is
Output difference data between frame data and predicted current frame data
Force The differential cosine conversion means
Data, Apply discrete cosine conversion processing
By this, discrete cosine transform coefficient data
ProducesBy the quantizing means, Based on the specified quantization step
The discrete cosine transform coefficient data
The quantization discretionary
Generate Tocosine transform coefficient data,The pre-prediction frame data generation means uses the quantization data
Inverse cosine transform coefficient data, inverse quantum
Processing, inverse discrete cosine transform processing
To generate pre-prediction frame data, The pre-prediction frame is generated by the prediction current frame data generation means.
The motion vector of the frame data and the current frame data
By detecting it, the
Motion compensation of the current frame data
Generate the current frame data, By control meansIn the above quantization meansQuantizing
Control and In the control means, the macroblock of the current frame
image dataAnd the predicted current frame
When using the motion vector detected by the data generation means
Image data of macroblock of predicted current frameIs the first
With 2 dataBased on the difference of, The first data and before
Indicates changes in the contents of the second dataGenerate evaluation data
Based on the above evaluation dataSupplied to the above quantization means
BeCoding characterized by controlling the quantization step
Method.