JPH0595542A - Dynamic picture coder-decoder - Google Patents

Abstract

PURPOSE:To provide the transfer picture with high picture quality by a small amount of information by performing proper quantization while trasferring the predictive value and the quantization width of the block to be predictive- coded or the predictive value and the dynamic range of the block. CONSTITUTION:A coder 2A consists of a difference data generation circuit 3, a changeover circuit 4, a discrete cosine conversion processing part 5, and a predictive coding processing part 6. The picture is divided into unit blocks composed of a plurarity of picture elements. In performing the coding for each unit block, the proper changeover of the discrete cosine conversion encoding and the predictive coding is performed. Further, the system of the variable length coding is changed according to the changeover of the discrete cosine conversion coding/predictive coding. In the case of discrete cosine conversion coding, the two-dimensional variable length coding is performed on the combination between the zero run and the picture element value. In the case of the predictive coding, the two-dimensional variable length coding is performed on the combination of the differential value between the zero run and the picture element value.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Field of Industrial Application Conventional Technology Problems to be Solved by the Invention Means for Solving the Problems (FIGS. 1 and 2) Action (FIG. 17) Example (FIGS. 1 to 17) (1) Overall configuration (FIG. 1 and FIG. 2) (2) Configuration of Encoding Device (FIG. 1) (2-1) Configuration of DCT Processing Unit 5 (FIG. 1) (2-2) Processing of Predictive Encoding Processing Unit 6 (FIG. 3 and FIG. 4) (2-3-1) Method of using average value of image signal in block as prediction value (FIGS. 5 to 7) (2-3-2) Prediction value using adaptive dynamic range coding Method for obtaining (FIGS. 8 and 9) (2-3-3-1) Edge matching quantization method (1)
(FIGS. 10 to 12) (2-3-3-2) Edge matching quantization method (2)
(FIG. 13) (2-4) Processing of DPCM circuit 25 (2-4-1) DPCM method (1) (FIG. 14) (2-4-2) DPCM method (2) (FIG. 14) (2-5 ) Processing of DCT / prediction coding determination circuit 7 (2-5-1) Determination in spatial domain (2-5-2) Determination in DCT conversion output domain (FIG. 15) (2-6) VLC circuit 10 Processing (2-6-1) VLC system (1) (2-6-2) VLC system (2) (FIG. 16) (3) Configuration of decoding device (FIG. 2) (4) Operation of embodiment (FIG. 16 and FIG. 17) (5) Effect of the embodiment (6) Other embodiment Effect of the invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for application to a moving picture coding apparatus that codes a moving picture with high efficiency and transmits the moving picture.

[0003]

2. Description of the Related Art Conventionally, in a video signal transmission system for transmitting a moving image to a remote place such as a video conference system or a video telephone system, in order to efficiently use a transmission line, the video signal is transmitted between frames or within a frame. It is designed to enhance the transmission efficiency of important information by encoding. A typical two-dimensional Discrete Cosine Transform (DCT) system is a typical coding system for highly efficient coding of such coded data.

This Discrete Cosine Transform method is
The amount of information is compressed by concentrating signal power on a specific frequency component using the two-dimensional correlation of an image signal and encoding only the concentrated distribution coefficient. For example, the distribution of DCT coefficients concentrates on low-frequency components in a portion where the pattern is flat and the autocorrelation of the image signal is high. In this case, the amount of information is compressed by encoding only the coefficients distributed in the low frequency range. Is made possible.

On the other hand, in a pattern with many edges, the coefficients are widely dispersed from low frequency components to high frequency components at the discontinuity points of the edges. In this case, in order to accurately represent the discontinuous point of the image signal with the DCT coefficient like an edge, a very large number of coefficients are required, so that the coding efficiency is lowered. At this time, if the quantization characteristic of the coefficient is roughened for high compression coding of the image or the coefficient of the high frequency component is discarded, the deterioration of the image signal becomes noticeable. For example,
The ringing becomes noticeable visually.

On the other hand, there is a predictive coding method as a moving picture coding method. With this predictive coding method, a transmission image can be coded with relatively high efficiency for a correlated pattern. However, when the correlation is small, there is a problem that the amount of information increases and the transmission efficiency decreases. Therefore, it has been proposed to improve the transmission efficiency by switching the encoding method of the transmission image in block units.

[0007]

However, when trying to predictably code a transmission image in block units, there is a problem that block distortion is conspicuous. Here, the block distortion means a phenomenon that an image partially looks like a mosaic for each block as a result of encoding.

This is because the predictive coding compresses the redundancy of only the amplitude of the image signal, and block distortion is likely to occur when the compression rate is increased as compared with the discrete cosine transform method which compresses up to the spatial frequency domain. This is because. In this way, when switching between the discrete cosine transform method and the predictive coding method in block units,
When the image is encoded and transmitted by simply switching to the one having higher encoding efficiency, the encoding efficiency is improved, but there is a problem that the image is deteriorated due to block distortion of the decoded image.

The present invention has been made in consideration of the above points, and an object thereof is to propose a moving picture coding apparatus capable of obtaining a high quality transmission image with a small amount of information.

[0010]

In order to solve such a problem, in the first invention, an image is divided into unit blocks corresponding to a plurality of pixels, and the pixel data of the pixel is intra-frame coded or inter-frame coded. In the moving picture coding / decoding device 1 for converting and transmitting, the pixel data of the unit block is discretized cosine transform coded S21 or predictive coding S7 according to the unit block, and the discrete cosine transform code of the unit block is sent. In the case where the switching information S5 is transmitted in response to the switching of the encoding S21 or the predictive encoding and the pixel data is discrete cosine transform encoded, the two-dimensional variable of the combination of the zero value length of the pixel data and the pixel value is performed. In the case of long-coded transmission or decoding and predictive coding of the pixel data,
A combination of the length of the zero value and the difference value of the pixel values is two-dimensionally variable length coded for transmission or decoding.

In the second aspect of the invention, when there is a discontinuity in the pixel information in the unit block, the pixel data of the unit block is predictively encoded and transmitted instead of the discrete cosine transform encoding. To do.

[0012]

When one image is divided into blocks and is coded in block units, the discrete cosine transform coding and the predictive coding are switched according to the nature of the pattern, and the predictive coding in the block unit occurs. In order to reduce block distortion (discontinuity between blocks), in the block for predictive coding, the block prediction value and the quantization width, or the block prediction value and the dynamic range are transmitted to perform adaptive quantization. As a result, the decoding apparatus can obtain a high-quality image by decoding the image using the switching information, the block prediction value and the quantization width, or the block prediction value and the dynamic range.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings.

(1) Overall Structure In FIGS. 1 and 2, reference numeral 1 denotes an image data transmission system as a whole, and an encoding device 2A encodes image data within a frame (field) or between frames (field) and after encoding. The transmission image is transmitted by appropriately switching the discrete cosine transform coding process or the predictive coding process for each block.

The coding device 2A adds this switching information to the switching information flag for discrete cosine transform coding or predictive coding for each area to be coded, or an information flag indicating the case classification of the area to be coded. Is extended to provide a mode of predictive coding. Further, the decoding device 2B is adapted to decode the transmission image by using these information flags transmitted together with the encoded image data.

(2) Configuration of Encoding Device The encoding device 2A receives the image data of 8 × 8 pixels as the input digital data S1 and performs the discrete cosine transform via the difference data generating circuit 3 and / or the switching circuit 4. The processing unit 5, the predictive coding processing unit 6, and the DCT / predictive coding determination circuit 7 are supplied to the respective units. The difference data generation circuit 3 uses the input digital data S1.
And the difference between the prediction data S2 input from the prediction circuit 8 and the difference data S3 are output to the switching circuit 4.

The switching circuit 4 uses the inter-frame / intra-frame coding switching signal S4 input from the prediction circuit 8 to input the input digital data S1 when the intra-frame coded data can be transmitted with a smaller data amount. The difference data S3 is output when it can be output as it is, or when it can be transmitted with a smaller data amount by inter-frame encoding and transmission.

Here, the DCT processing section 5 utilizes the two-dimensional correlation of the input image to perform the discrete cosine transform of the input image data S1 or the difference data S3 in the unit of a minute block, and the transformed data obtained as a result is subjected to a predetermined conversion. When quantized with the quantization size, the variable length coding circuit 1 is passed through the switching circuit 9.
It is designed to output to 0.

Further, when the predictive coding unit 6 predictively codes the image signal in the block, the predictive coding unit 6 obtains the difference between the predicted value and the current image signal, quantizes the difference signal with a predetermined quantization size, and switches it. It is adapted to output to the variable length coding circuit 10 via the circuit 9. The DCT / predictive coding determination circuit 7 determines whether to perform discrete cosine conversion in block units or predictive coding in block units when coding an image signal, and the determination result is switched to DCT / predictive coding. The signal S5 is output.

As a result, the switching circuit 9 outputs the conversion data S6 output from the DCT processing unit 5 when the discrete cosine conversion data is to be output.
When the predicted coded data is to be output to 0, the converted data S7 output from the predictive coding processing unit 6 is output to the variable length coding circuit 10.

Here, the variable length coding circuit 10 has a conversion table corresponding to the DCT conversion data S6 and the predictive coding conversion data S7 having different statistical properties and switching controlled by the DCT / prediction coding switching signal S5. Then, the conversion efficiency is further improved by the conversion table and output as the transmission data S8.

The buffer circuit 11 also transmits the transmission data S8.
After it is stored in the memory, it is output in a predetermined order, and a quantization width control signal for controlling the quantization size is output so that the residual data remaining in the memory has an appropriate remaining amount. ing. Here, the encoding device 2A is
D through the inverse quantization circuit 12 and the inverse DCT circuit 13 in sequence
The quantized data S10 input from the CT processing unit 5 is inversely quantized into a representative value, and the locally decoded image data S11 is further subjected to the inverse transform process of the discrete cosine transform.
It is designed to be converted to and output.

Further, the encoding device 2A includes an inverse quantization circuit 14
Then, the quantized data S12 input from the predictive encoding processing unit 6 through the inverse predictive encoding circuit 15 is inversely quantized into a representative value, and further the decoded image data S13 is obtained by the conversion processing opposite to the predictive encoding processing. It is designed to be converted to and output. The switching circuit 16 outputs the decoded image data S11 when the input image is DCT-converted and transmitted based on the DCT / predictive coding switching signal S5, and the input image is predictively coded and transmitted. In such a case, the decoded image data S13 is converted and output to the addition circuit 17.

Here, the adder circuit 17 adds the image data S14 input from the switching circuit 18 and the decoded image data S11 or S13 to obtain the locally decoded data S15 as the prediction circuit 8.
It is designed to be supplied to. Here, the prediction circuit 8
The prediction data S2 is supplied to the difference data generation circuit 3 and the switching circuit 18 based on the locally decoded data S15, and
The motion vector / prediction mode determination signal S16 is output to the variable length coding circuit 10 based on the locally decoded data S15.

(2-1) Configuration of DCT Processing Unit 5 The DCT processing unit 5 has a DCT circuit 20, a quantization circuit 21 and a delay circuit 22, and the DCT circuit 20 uses the two-dimensional correlation of the input image. And input digital data S1
Alternatively, the difference data S3 is converted into the discrete cosine conversion data S21 and output to the quantization circuit 21 (Journal of the Institute of Electronics, Information and Communication Engineers 1987/1 Vol.J70-
B No. 1 p96-104 “Intra-frame / inter-frame adaptive extrapolation interpolative coding of HDTV signal” and Japanese Patent Application No. 2-41024
No. 7).

The quantizing circuit 21 quantizes the discrete cosine transformed data S21 in accordance with the amount of generated information and outputs the quantized data S10 to the delay circuit 22 and the inverse quantizing circuit 12. Delay circuit 22
Is configured to delay the quantized data S10 by a delay time corresponding to the processing time of the predictive coding processing unit 6 and output the quantized data S10 to the variable length coding circuit 10.

Incidentally, it is known that the DCT method generally has a property that a large value is concentrated around a certain coefficient by performing DCT on a signal whose brightness changes smoothly. For example, as shown in FIG. 3 (A), an original image having a luminance level of 30 to 100 in which each pixel is a pattern including edges from the upper left to the lower right as one block of 8 × 8 pixels is input. In this case, when the discrete cosine transform is performed by the DCT circuit 40, most of the coefficients in the block become 0 (FIG. 3 (B)). Further, the coefficient having the value exists on the diagonal line from the upper left to the lower right.

Next, when this coefficient is quantized by the quantizer circuit 21 with a brightness level of 10, for example, most of the coefficients become 0 and only large coefficients remain. Therefore, the coefficients are sequentially called according to the calling sequence of the illustrated coefficients (the numbers indicate the calling order), and the variable length coder (VLC) is used.
High-efficiency coding can be achieved by coding with a variable-length coding system such as Huffman code according to 10.

At this time, taking into consideration that pixels have a correlation in a two-dimensional direction, it has been proposed to call a coefficient that is gradually distant from a coefficient calling start point. Further, in the case of a pattern having a strong coefficient correlation in the horizontal direction, the coefficients in the upper stage (0 to 7) of the block can be sequentially called in the reading order as shown in FIG. 4, and subsequently can be called as (8 to 63).

(2-2) Processing of Predictive Encoding Processing Unit 6 The predictive encoding processing unit 6 has a predictive encoding circuit 23, a quantizing circuit 24 and a DPCM (Differntial PCM) circuit 25. When the predictive coding processing unit 6 predictively codes the image signal in the block, the predictive coding processing unit 6 generates a differential signal of the block from the image signal information in the block and quantizes it to generate DPCM.
High-efficiency coding is performed by reducing autocorrelation left in the differential signal by the circuit 25 and coding the data by the variable-length coding circuit 10 (JP-A-1-135281). JP-A-2-134910
Publication).

At this time, the buffer circuit 11 monitors the output data and, depending on the amount of information, the quantization width Q of the predictive coding circuit 23.
Is made to decide. Specifically, the following three methods can be used as the adaptive quantization method. In the present invention, one or more of these methods are selectively used for each block.

(2-3-1) Method of using the average value of the image signal in the block as the predicted value, that is, as shown in FIG. 5, the average value of the amplitudes of all the pixels in the block is calculated, and the average value and the average value are respectively obtained. This is a method of quantizing the difference in signal level between pixels. Here, the quantization width Q is a value output from the buffer 11. At this time, if the average value in the block is M and the signal level of the pixel in the block is L, the quantization code Lq is

[Equation 1] It is represented by. Here, // indicates rounding off to the first decimal place.

If the restoration value is L ',

[Equation 2] Can be expressed as (FIG. 6). However, in this method, when the quantization width Q is large, the restoration value distortion becomes large, and discontinuity between blocks tends to occur as shown in FIG.

(2-3-2) Method of Obtaining Prediction Value Using Adaptive Dynamic Range Coding (ADRC) This method is based on the "quantization method of adaptive dynamic range coding". Kondo et al., 19
In 1989, it is disclosed in the 4th Image Coding Symposium (PCSJ) Material (4-3).

Adaptive Dynamic Range Coding ADR
FIG. 8 shows the quantization characteristic when C is applied, and FIG. 9 shows an example of the block distortion caused by the adaptive dynamic range coding ADRC. In the adaptive dynamic range coding ADRC, the reason why the minimum value in a block is used as a prediction value is that the minimum value is often located in the peripheral portion of the block.

That is, since the normal block is a small area of about 8 × 8 pixels, when the brightness level is concave, it is extremely low. For this reason, the minimum value of a certain block is often close to the minimum value of any of the surrounding blocks. Therefore, when the minimum value is in the peripheral portion of the block, the continuity with at least one peripheral block is maintained, and the block distortion is suppressed to the minimum.

Further, in the adaptive dynamic range coding ADRC, as shown in FIG. 8, the average value of the signal values included in the highest and lowest gradation levels is newly added to the maximum value.
Redefining the minimum value makes it less susceptible to noise and isolated points (JP-A-2-134910).

(2-3-3-1) Edge Matching Quantization Method (1) First, the one-dimensional case will be described. With respect to the block length signal as shown in FIGS. 10 and 11, the signal values at both ends of the block are set to X1 and X2, and X1 ≦ X2 is set for simplification, and the restoration values of the signal values X1 and X2 are determined. The quantization width Q output from the buffer 11 is changed by the following algorithm so that it is output below the error.

If the signal level of the pixel in the block is L and the restoration error tolerance of the signal values X1 and X2 is Ex, the dynamic range DR is

[Equation 3] And the quantization width Q and the signal value X1 are

[Equation 4] And,

[Equation 5] Then, the quantization width Q is set to the same value as the quantization width q indicated by the quantization width control signal S22 output from the predictive coding circuit 23 to the quantization circuit 24, and the signal value X1 is left unchanged.

[0040] Also

[Equation 6] And

[Equation 7] Then, the quantization width Q and the signal value X1 are left unchanged. Here, ABS represents an absolute value.

Where

[Equation 8] Then, the quantization width Q is left unchanged and the signal values X1 and X
When the average value of 2 is Xm = (X1 + X2) // 2, the signal value X1 is Xm. However, the quantization width q specified by the predictive coding circuit 23 is defined as follows for all the quantization width Q and dynamic range DR.

[Equation 9] The table is written in the ROM by finding a value larger than Q that satisfies the above condition.

At this time, the quantization code Lq is

[Equation 10] And the restored value L'is

[Equation 11] Given by. In this method, since the error of the restored signal at both ends of the block is suppressed by Ex, the continuity between blocks can be further maintained.

Next, a two-dimensional case will be described. To extend the one-dimensional method to a two-dimensional block, X1, X
2 A sub-routine for making a decision is further required. The algorithm for this determination is as follows. First 8x
As for the two-dimensional block signal of 8 pixels, as shown in FIG. 12, areas 1a, 1b, 2a, 2b, 3a, 3b, 4 at the end of the block
Consider a and 4b.

Next, the average value of the pixel values in each area is calculated for each area. Here, each of these average values is m
1a, m1b, m2a, m2b, m3a, m3b, m4
a and m4b. After this, ABS (m1a-m1
b), ABS (m2a-m2b), ABS (m3a-m)
3b) and ABS (m4a-m4b), the largest one is obtained.

By the above procedure, the direction in which the pixel values greatly differ at both ends of the block, that is, the direction across the edge is obtained. Therefore, the smaller one of the representative values of the pixels in the selected two regions is set to X1, the other is set to X2, and the block signal is quantized in the same manner as in the one-dimensional case.
Dequantize.

(2-3-3-2) Edge Matching Quantization Method (2) First, the one-dimensional case will be described. For a block length signal as shown in Fig. 13, set the signal values at both ends of the block to X.
1 and X2. For simplicity, X1 ≦ X2. This method is characterized in that the decoder side changes the restoration values so that the signal values X1 and X2 are output as the restoration values as they are. When the signal level of the pixel in the block is L, and the quantization width output from the buffer 11 is Q, the quantization code Lq is

[Equation 12] Becomes

Here, in the encoding device 2A, the quantized code L
In addition to q, the signal values X1, X2 and the quantization width Q are transmitted as quantization parameters. In the decoding device 2B, the signal values X1 and X2 and the quantization width Q are received as the quantization parameter, and first, the quantization value X of the signal value X2 is received.
It is designed to calculate 2q.

[Equation 13]

After this, the quantization code Lq becomes the quantization value X2.
If it is equal to q,

[Equation 14] And if they are not equal,

[Equation 15] Is restored to the restored value L ′. This method has a simpler algorithm than the edge matching quantization method (1) described above, and does not require a ROM table for changing the quantization width Q.

Next, a two-dimensional case will be described. When the edge matching quantization method (2) is extended to a two-dimensional block signal, X1 and X2 are determined by the method described in the edge matching quantization method (1). Subsequent quantization and decoding methods are performed in the same manner as in the one-dimensional case.

(2-4) DPCM (Differntial PCM)
Processing of Circuit 25 The coefficients after adaptive quantization still have almost the same autocorrelation of the signal that the original image signal had. Therefore, the amount of information can be further compressed by performing DPCM in the subsequent stage. In the DPCM circuit 25, the scan direction of the input pixel is designated by the scan signal S24 from the predictive coding circuit 23.

The DPCM circuit 25 obtains the difference between the quantized image signal Yi input by the differentiator and the pixel value one pixel before,

[Equation 16] Is designed to get you.

The prediction error signal Ei can take values from -255 to +255 when the input signal is 8 bits. Therefore, if it is attempted to transmit the data as it is, 9 bits are required, and an extra code is required for each pixel. However, it is known that the prediction error signal is mostly centered around zero and before and after it. Therefore, not all signals are represented by 9 bits, but by assigning a code with a short bit length to the signal values that appear in large numbers, the block as a whole will have an average of 9 bits as well as the original input signal of 8 bits. A block signal can be represented with a bit length much shorter than that.

Here, the following three methods can be used as a method suitable for the DPCM in the block. In the present invention,
One of the following methods is selectively used for each block.

(2-4-1) DPCM method (1) DPCM of the block signal after adaptive quantization is performed in the calling path as shown in FIG. Since there is only one call path, the circuit configuration is simple. However, except for the block including the contour like the mode 1 in FIG. 14A (mode 2 in FIG. 14B, mode 3-1 in FIG. 14C, mode 3-2 in FIG. 14D). Therefore, it is not possible to expect a significant amount of information compression.

(2-4-2) DPCM method (2) Then, it is considered to switch the data calling method for each of the modes 1 to 3-2 so that the optimum amount of information can be compressed. FIG. 14 shows a calling method suitable for each of the modes 1 to 3-2. Next, a method of determining mode switching of these DPCM will be described. This determination is made by supplying the DPCM circuit 25 with the information obtained by the examination of the directionality of the contour in the block signal described in the edge matching quantization method (1).

That is, when i = 1, mode 1 is set, and i =
Mode 2 when 2 and mode 3-1 when i = 3,
Further, when i = 4, it corresponds to mode 3-2.

(2-5) Process of DCT / Predictive Coding Determination Circuit 7 When the image signal is coded, the DCT / predictive coding determination circuit 7 performs DCT in block units or predictive coding. It is determined whether or not to convert. First, it is necessary to judge which processing method should be selected based on the block information. In that case, the determination is made in the spatial domain or the DCT transform output domain. Each determination method will be described in detail below.

(2-5-1) Judgment in Spatial Area For a picture whose brightness changes abruptly, specifically, an image including edges and details, the dynamic range (maximum value-minimum value) of the image signal in the block is determined. Value) takes a large value.
For such a pattern, the DCT has a disadvantage in the compression rate of information, and the predictive coding should be selected. Therefore, for each block, the dynamic range (DR) within that block is obtained, and it is determined that the predictive coding is performed for the block whose value exceeds an appropriate threshold value (A) selected from the compression rate and the deterioration of the pattern. To do.

(2-5-2) Determination in DCT Transform Output Area It is known that the DCT coefficient when the image signal is two-dimensionally DCT has the following properties. For example, in a two-dimensional DCT having (8 × 8) pixels as a block (macro block), the coefficient F at the 0th row and 0th column corresponding to the upper left corner of the block
(0, 0) corresponds to a DC component that represents the average brightness in the image block. The coefficient represents the vertical high frequency component in the image block as it goes from F (0,0) to the right and horizontal direction, and the horizontal high frequency component as it goes downward.

That is, when a block of a pattern whose brightness changes abruptly like an edge is transformed by Discrete Cosine, the converted output is largely as shown in FIG.
Can be classified into two. FIG. 15 shows an output area after the discrete cosine conversion in the macro block of 8 × 8 pixels. Here, ◯ indicates the position of a pixel with high (or low) brightness, and × indicates the position where a large DCT coefficient is likely to occur in the block.

FIG. 15A shows the case where the contour exists in the vertical direction, and the DCT coefficients concentrate from the low order to the horizontal direction with large energy. This is hereinafter referred to as "case 1". Further, in FIG. 15B, when the contour exists in the horizontal direction, the DCT coefficient concentrates with a large energy in the vertical direction from the low order. This is hereinafter referred to as "case 2".

In FIG. 15C, when the contour exists in the diagonal direction, the DCT coefficient concentrates with a large energy in the diagonal direction from the low order. Hereinafter, this will be referred to as "case 3". All DC except DC components
Absolute value sum Fa of T coefficient and D of the DCT output area in each of the cases 1, 2, and 3
The absolute value sums F1, F2, and F3 of CT coefficients are obtained for each block.

When the maximum of the absolute value sums F1, F2, and F3 is Fmax, the predictive coding is performed for blocks in which the ratio of Fmax to Fa exceeds an appropriate threshold value selected from the compression rate and the deterioration of the pattern. It is adapted to be encoded by the method.

(2-6) Structure of VLC Circuit 10 (2-6-1) VLC (Variable Length Coding) Method (1) Since the statistical properties of the signals of the Discrete Cosine Transform coding and the predictive coding are different, It is designed to further improve the coding efficiency by preparing a table of codes used for the modulatable coding for each and selectively using it according to the switching signal of DCT / prediction coding.

(2-6-2) VLC system (2) In the VLC system (1), only the table of codes used for variable length coding is properly used, but the VLC system (2)
Then, depending on the switching of DCT / prediction coding, VLC
The encoding method of the circuit 10 is switched. That is, in the case of Discrete Cosine Transform coding, zero-run and level two-dimensional variable-length coding / decoding is performed, and in predictive coding, two-dimensional variable-length coding / decoding of zero-run and level difference values. It is done like this.

For example, as shown in FIG. 16, when the signal in which the inter-frame difference signal is encoded is input to the VLC circuit 10, the correlation between the pixels which cannot be excluded even by the inter-frame difference with motion compensation is included in this signal. Remains locally (non-zero part in the figure). The encoding of this signal requires encoding that locally reduces the correlation, and the VLC circuit 10 is adapted to perform encoding by the following algorithm.

That is, when the pixel to be encoded is zero, the length of zero run is counted up and the pixel data is not encoded. When the pixel to be encoded is not zero and the previous pixel is zero, the zero-run length up to that point and the pixel value (level) are paired to perform two-dimensional variable length encoding. When the pixel to be encoded is not zero and the previous pixel is not zero, the difference from the previous pixel is calculated (DPCM), and the zero run length up to that point and the difference value between the pixel value (level) are combined. Then, two-dimensional variable length coding is performed.

(3) Configuration of Decoding Device On the other hand, the decoding device 2B, as shown in FIG. 2, has the encoded bit stream input S3 output from the encoding device 2A.
1 is input to the buffer 31 and is temporarily stored. The inverse variable-length coding circuit 32 decodes from the switching signal whether the transmission data is DCT conversion data or predictive coding conversion data from the coding bit stream input S31, and according to the information, DCT or predictive coding. Or select.

Here, the inverse variable length encoding circuit 32 is adapted to inverse variable length encode the encoded bit stream input S31 and supply it to the inverse DCT processor 33 and the inverse prediction encoding processor 34. .. The inverse DCT processing unit 33 has a delay circuit 35, an inverse quantization circuit 36, and an inverse DCT circuit 37, and decodes a transmission image from the encoded bit stream input S20 by a processing procedure reverse to that of the DCT processing unit 5. ing.

Further, the inverse predictive coding processing section 34 uses the inverse DPC.
M circuit 38, inverse quantization circuit 39, inverse prediction encoding circuit 40
And the transmission image is decoded from the encoded bit stream input S31 by a processing procedure reverse to that of the predictive encoding processing unit 6. Here, the inverse quantization circuits 36 and 3
Reference numeral 9 denotes the quantization width control signal S from the inverse variable length coding circuit 32.
32 and S33 are input.

The inverse DPCM circuit 38 is adapted to receive the scan direction designating signal S34 from the inverse variable length encoding circuit 32, and the inverse predictive encoding circuit 40 is adapted to input the predicted value signal S35. ing. The decoding device 2B has the decoded data S36 decoded by the inverse DCT processing unit 33 and the inverse predictive coding processing unit 34 by the processing procedure.
And S37, the transmission image is decoded through the switching circuit 41 and the adding circuit 42 in order.

At this time, the predicting circuit 43 is switched and controlled by the inverse variable length encoding circuit 32, and reproduces the moving image from the output of inverse DCT or inverse predictive encoding processed for each block. Is. Here, the output of the prediction circuit 43 is added via the switching circuit 44 to the addition circuit 42.
Is input to the switching circuit 41,
42 are switched by the DCT / prediction coding switching signal S39 input from the inverse variable length coding circuit 32.

(4) Operation of the Embodiment In the above configuration, the encoding device 2A switches the switching circuit 4 by the inter-frame / frame timing switching signal S4 input from the prediction circuit 8 so that frames are transmitted in accordance with the transmitted image. The inter-frame coded or intra-frame coded image data is output to the DCT processing unit 5 and the predictive coding processing unit 6.

At this time, the DCT processing section 5 performs discrete cosine transform on the image data of 8 × 8 pixels by utilizing the two-dimensional correlation, and the transformed image data is further controlled by the quantization width control input from the buffer circuit 11. Quantize based on the signal S9. Further, the predictive coding processing unit 6 supplies the DPCM circuit 25 with quantized data S10 obtained by quantizing the predictively coded image data with a predetermined quantization width through the predictive coding circuit 23 and the quantizing circuit 24 in sequence. However, the amount of image data is further reduced.

When the variable length coding circuit 10 receives the coded data coded by the DCT processing unit 5 or the predictive coding processing unit 6 through the switching circuit 9, the VLC system (1) or the VLC system is input. Based on (2), the image data of 8 × 8 pixels is subjected to variable length coding processing. That is, when the 8 × 8 pixel signal given in FIG. 16 is encoded by this algorithm, the first non-zero signal is “2” in the first row and fourth column, so the length of zero run up to that point is paired with 3. Thus, the code gets (3, 2).

The next pixel value is "2" in the first row and fifth column, but when the difference is taken, it is "0", and it is set to (0, 0) in combination with the zero run length "0". Since the next pixel value is “3” in the first row and sixth column, the difference is “1”, and the zero run length “0” is paired with (0, 1). When a code is generated by this algorithm, it becomes as shown in FIG.

Comparing normal zero run and level two-dimensional variable-length coding (FIG. 17B), * is added to the group concentrated near 0 for normal zero run and level coding. In other words, it is possible to reduce the code amount as a whole by taking the level difference value due to the effect of the variable length coding. At this time, to combine the zero-run and level two-dimensional variable-length coding schemes with the zero-run and level difference value two-dimensional variable-length coding schemes, zero-run length 0 is used.
All other codes can be shared by adding only one code of (0, 0) in which the difference value and the difference value are 0.

In order to combine the two-dimensional variable-length coding method of zero run and level with the two-dimensional variable-length coding method of difference value of zero run and level, only one circuit and a code for taking a difference are added. So the increase in hardware is
Very few. With this method, the correlation between pixels that cannot be removed even with the inter-frame difference with motion compensation is removed, and further compression can be performed as compared with the method using only two-dimensional variable length coding of zero run and level.

(5) Effects of the Embodiments According to the above configuration, when transmitting a signal including a discontinuity point such as an edge, switching to predictive coding enables information to be equal to or less than that of DCT coding. The amount of coding enables DCT with less interference such as mosquito noise.
Compared with a system that only encodes, a high image quality can be transmitted with a small amount of information as a whole. In addition, when predicting and encoding the transmitted image, block prediction value and quantization width (or block dynamic range) are transmitted, and adaptive quantization is performed to reduce block distortion of the decoded image. You can

(6) Other Embodiments In the above embodiment, two types of tables for codes used in the VLC circuit 10 may be prepared: one for zero run and level and one for difference value between zero run and level. But,
Only one type of table may be used and the reading may be changed depending on the method.

For example, a zero run and level VLC circuit 10
The code of (0, 1) in the table used for is assigned to (0, 0) of the VLC circuit 10 of the difference value between the zero run and the level, and the code of (0, 2) of the zero run and the level is calculated as the difference between the zero run and the level. By allocating to the values (0, 1) and using the codes in order while shifting them, it is possible to perform two variable length codings with one code table without rewriting the codes.

[0082]

As described above, according to the present invention, the transmission image is coded by switching between the discrete Cothan transform system and the predictive coding system in block units, the switching information is transmitted for each block, and the code is transmitted. In the case of switching the variable length coding method according to the coding method and coding with the Discrete Cosin conversion method, two-dimensional variable length coding processing is performed for zero run and level, and when coding with the predictive coding method. Is 2 for the difference between zero run and level
By transmitting the transmission image by the dimensional variable length encoding process, the encoding efficiency can be further improved and the image quality can be further improved as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an encoding device according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a decoding device according to the present invention.

FIG. 3 is a diagram for explaining changes in DCT coefficients due to the discrete cosine transform.

FIG. 4 is a diagram for explaining a calling order of coefficients.

FIG. 5 is a characteristic curve diagram for explaining the average value prediction.

FIG. 6 is a characteristic curve diagram for explaining a quantization / decoding characteristic based on average value prediction.

FIG. 7 is a characteristic curve diagram for explaining the block distortion when the average value prediction is used.

FIG. 8 is a characteristic curve diagram showing a quantization characteristic by adaptive dynamic range coding.

FIG. 9 is a characteristic curve diagram for explaining block distortion when adaptive dynamic range coding is used.

FIG. 10 is a characteristic curve diagram for explaining the edge matching quantization method (1).

FIG. 11 is a characteristic curve diagram for explaining a quantization characteristic by the edge matching quantization method (1).

FIG. 12 is a diagram showing a region in a case where the edge matching quantization method (1) is applied to two-dimensional encoding.

FIG. 13 is a characteristic curve diagram for explaining an edge matching quantization method (2).

FIG. 14 is a diagram for explaining a coefficient call path by DPCM.

FIG. 15 is a diagram showing a relationship between edges and DCT coefficients.

FIG. 16 is a diagram for explaining a difference between frames by the variable length coding process.

FIG. 17 is a characteristic curve diagram provided for explaining a variable length coding process according to the present invention.

[Explanation of symbols]

1 ... Image data transmission system, 2A ... Encoding device,
2B ... Decoding device, 5 ... DCT processing unit, 6 ... Predictive coding processing unit, 7 ... DCT / predictive coding determination circuit, 8
... prediction circuit, 10 ... VLC circuit, 11, 31 ... buffer circuit, 12, 24, 36, 39 ... dequantization circuit, 15 ... deprediction coding circuit, 20 ... DCT circuit,
21, 24 ... Quantization circuit, 22, 35 ... Delay circuit,
23 ... Predictive coding circuit, 25 ... DPCM circuit, 37
...... Inverse DCT circuit, 38 ...... Inverse DPCM circuit, 40 ......
Inverse predictive coding circuit.

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[Procedure amendment]

[Submission date] September 4, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: Video coding / decoding device

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007]

However, since the predictive coding system compresses only the redundancy of the amplitude of the image signal,
The compression rate is lower than that of the discrete cosine transform method that compresses up to the spatial frequency domain, and there is a problem that high coding efficiency cannot be obtained by simply switching between the discrete cosine transform method and the predictive coding method. .

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Delete

[Procedure correction 4]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

[0012]

When one image is divided into blocks and is coded in block units, the discrete cosine transform coding and the predictive coding are switched according to the nature of the picture, and the variable length is changed according to the switching. By switching the encoding method, the encoding efficiency can be improved and the overall image quality can also be improved.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0075

[Correction method] Change

[Correction content]

When the variable length coding circuit 10 receives the coded data coded by the DCT processing unit 5 or the predictive coding processing unit 6 via the switching circuit 9, the VLC system (1) or the VLC system is inputted. Based on (2), the image data of 8 × 8 pixels is subjected to variable length coding processing. That is, the determination circuit 7
When it is determined that the predictive coding is to be performed in, the 8 × 8 pixel signal coded by the predictive coding processing unit 6 and given in FIG. 16 is variable length coded by this algorithm. As a result, the first non-zero signal is "2" in the first row and fourth column, so the pair is combined with the length of zero run up to that point to obtain the code (3, 2).

Claims (2)

[Claims] 1. A moving picture coding / decoding apparatus which divides an image into unit blocks corresponding to a plurality of pixels and intra-frame-codes or inter-frame-codes pixel data of the pixels and transmits the unit data. Accordingly, the pixel data of the unit block is discretized cosine transform coded or predictively coded, and the switching information is transmitted according to the discreet cosine transform coding or the predictive coding of the unit block, and the pixel In the case of discrete cosine transform coding of data, in the case where the combination of the zero value length of the pixel data and the pixel value is two-dimensionally variable length coded, transmitted or decoded, and the pixel data is predictively coded. 2 for the combination of the length of the zero value and the difference value of the pixel value.
A moving picture coding / decoding apparatus, characterized in that it is dimensionally variable length coded for transmission or decoding. 2. When the pixel information in the unit block is a discontinuity point, the pixel data of the unit block is predictively encoded and transmitted instead of discrete cosine transform encoding. The moving picture coding / decoding apparatus according to Item 1.