JPH03124182A - Cell abort compensation picture decoding system - Google Patents

Abstract

PURPOSE:To reduce the effect of cell abort onto picture quality by keeping a DC component in a relevant block in a preceding frame with respect to a block whose data is not entirely received by cell abort and making its AC component zero. CONSTITUTION:An abort compensation means 12 in a decoding section 15 uses a quantizer at a sender side so as to use a reception picture data returned to a signal of an original form from a quantized signal and detects the presence of cell abort in a transmission line and when the cell abort exists, all coefficients representing the AC component are cleared into 0 for the data of a coefficient area of the block corresponding to the block in a preceding frame to a frame including the block corresponding to the abort cell, the DC component coefficient is left as it is and the other coefficients are made entirely 0 and the result is outputted to an inverse orthogonal conversion section 11. Thus, no pattern exists in the block and the signal is displayed on a display screen in a uniform color.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a cell discard compensation image decoding method when cell discard occurs in an image data transmission system in which input image data is encoded using a plurality of pixels as blocks and transmitted in units of cells. , The purpose is to erase the pattern before cell discard by clearing the AC component of the data in the corresponding block in the frame before the block where the cell was discarded to 0 and outputting that data. an inverse orthogonal transform unit that orthogonally transforms input image data using pixels as blocks, encodes coefficients in the orthogonal transform coefficient region, transmits them in cell units, performs inverse orthogonal transform on the received data to the receiving side, and outputs image data. In an image data transmission system having an image data transmission system, the receiving side of the image data transmission system detects the presence or absence of discarded cells, and when there is discarded cell, a frame that is one frame before the frame containing the block corresponding to the discarded cell is sent to the receiving side of the image data transmission system. The decoded data of the coefficient domain of the block corresponding to the block is output to the inverse orthogonal transform unit (inverse orthogonal transform unit) with all coefficients representing AC components cleared to 0, and when there is no cell discard, the data after decoding is input. It is configured to have a discard compensation means for outputting the same as it is to the inverse orthogonal transform section.

[Industrial Application Field] The present invention relates to an image data transmission method, and more specifically, the present invention relates to an image data transmission method, and more specifically, to an image data transmission system in which input image data is encoded using a plurality of pixels as a block and transmitted in units of cells, in which cell discard occurs. The present invention relates to a cell discard compensation image decoding method for cases in which cells are discarded.

[Conventional technology]

Recently, the digitization of image equipment and the transmission method of image digital signals have been widely developed and researched in many application fields such as videophones. Generally, image data has a very large amount of information. For example, if current televisions were to be digitized as is, a transmission capacity of 100 Mb/s would be required, and image data has 1,500 times more information than audio. On a television, the screen changes 30 times per second, and frames change every 1/30 of a second. Pixels are generally arranged two-dimensionally on one screen corresponding to one frame, and even if the level of one pixel is represented by, for example, 8 bits, the amount of information in the image data for one frame is extremely large. There will be more.

However, even when frames are switched every 1730 seconds on a television, the content of the pictures in each frame often does not change significantly. In other words, there are many parts of the image that are completely static, such as the sky and background, and there are few parts that change from frame to frame.

Therefore, one method for compressing and encoding image data is an interframe encoding method.

In the interframe coding method, a difference in level data is determined for each corresponding pixel between two temporally consecutive frames, and the difference is subjected to, for example, Huffman encoding and sent onto a transmission path. If the level for most pixels does not change, the difference for those pixels will be 0, and the difference can be represented by one bit. Pixels with large level differences require codes of 8 bits or more, but by coding only these differences, the amount of information to be transmitted can be greatly compressed.

On the other hand, a method of encoding data within one frame as is is called an intraframe encoding method.

Regardless of whether interframe coding or intraframe coding is used, two operations, sampling and quantization, are basically required for digital representation of an image signal. There are two ways to sample an image; the first is to represent the image in terms of level values for discrete sequences of dots corresponding to pixels within a frame.

The second method is to perform orthonormal expansion of a level value function (image function) defined on the XY plane corresponding to the frame surface, and use the expansion coefficients as sample values.

FIG. 10 is an overall block diagram of an image transmission system using orthonormal transformation, which is the second method.

In FIG. 10, the input image is divided into blocks at 1, orthogonally transformed at 2, quantized at 3, and subjected to, for example, Huffman coding at 4, and sent from the sending side to the transmission line 5. Then, on the receiving side, the signal from transmission line 5 is decoded by 6, and 7
The data is inversely orthogonally transformed in step 8, converted into inverse blocks in step 8, and output as image data. Here, block 1 does not perform orthogonal transformation on two-dimensional KXK pixel data (for one screen), but instead transforms the data in units of blocks by treating approximately 4 x 4 to 16 x 16 pixels as one block. This is done to shorten the conversion time by determining .

Examples of the types of orthogonal transformations in 2 are Hadamard transform,
There are cosine transformations, Karhunen-Loewe transformations, etc.
In recent years, discrete cosine transform (DCT), which is a discrete representation of cosine transform and will be described later, is often used.

The orthogonal transform encoding method used in FIG. 10 focuses on the correlation between small areas within the screen, and orthogonal transform is performed using the pixels of the small area as a numerical string. The resulting conversion coefficients correspond to frequency components and represent each component from low frequency to high frequency. In image signals, the low frequency components are generally large in terms of power (the high frequency components are small in terms of power), so by performing quantization, which assigns a large number of bits to the low frequency components and a small number of bits to the high frequency components, transmission is reduced. The amount of information required is reduced.

FIG. 11 is a diagram showing a transform coefficient area after orthogonal transform is applied to image data in one block composed of 4×4 pixels. In this conversion coefficient region, the M region 9 at the top left generally represents the DC component of the signal, and the coefficients in the other regions all represent the AC component. The AC components correspond to each frequency from low frequency to high frequency, and the frequency becomes higher toward the lower right.

[Problem to be solved by the invention]

As described above, when transmitting image data by encoding multiple pixels in blocks, regardless of whether the encoding method is intra-frame or inter-frame, or whether it is in the orthogonal transform coefficient domain or pixel domain. Image data is transmitted on a transmission path in fixed-length packets of several bytes to which a header indicating a destination, called a cell, is added.

When cells with headers added in this way are transmitted within a network, if there is a header error or the number of cells increases to exceed the processing capacity of the network, cells will be discarded and the image will deteriorate in the receiving section. There was a problem. ? ! In a block encoding method that encodes i number of pixels as one block, conventionally, when cells are discarded, the data of the corresponding block in the frame one frame before the current frame is used as the image data of the discarded block. Since it was used as is, there was a problem in that the outline of the frame before cell discarding remained as it was.

For example, assume that half of the pixels in the corresponding block in the previous frame were black and half were white to form a pattern within the block, and all of the pixels in the next frame change to white. Considering this, when cell discard occurs, the data of the block of the previous frame is used as is, so the pattern before cell discard remains as is.

The purpose of the present invention is to erase the pattern before cell discard by clearing to 0 the AC component of the data in the corresponding block in the frame before the block where the cell was discarded and outputting that data. shall be.

[Means to solve the problem]

FIG. 1 is a block diagram of the principle of the present invention. This figure is a block diagram showing the configuration of a receiving side in an image data transmission system that encodes input image data using a plurality of pixels as blocks and transmits it in units of cells. FIG. 1 is a block diagram of the principle of the first invention, which corresponds to the case where input image data is orthogonally transformed, and coefficients in the orthogonal transform coefficient domain are encoded and transmitted. In the figure, the receiving side includes a decoding unit 15 that decodes the signal received from the transmission path 14, and an inverse orthogonal transformation unit 11 that inversely transforms coefficient data in the coefficient domain that has been orthogonally transformed into data in the pixel domain. be.

The discard compensation means 12 in the decoding unit 15 uses, for example, the received image data that has been decoded by a decoder and quantized by a quantizer on the transmitting side back to a signal in the original format, for example, for transmission. The presence or absence of cell discard on the road is detected, and when a cell is discarded, data in the coefficient area of the block corresponding to the block in the frame before the frame containing the block corresponding to the discarded cell is used to represent the AC component. All the coefficients are cleared to 0, that is, the DC component coefficient is left as is, and all other coefficients are set to O and output to the inverse orthogonal transform section 11.

FIG. 1(b) is a principle block diagram of the second invention, that is, the cell discard compensation image decoding method when coding in the pixel domain is used. In the figure, data received from a transmission path 14 is output as image data via a decoding section 15. The discard compensating means 13 in the decoding unit 15 uses data that is input from the transmission line 14, decoded, and returned to the format before quantization on the transmitting side, as in the first invention, to convert the data into cells. The presence or absence of cell discard is detected, and when a cell is discarded, the average value of data for all pixels constituting the block corresponding to that block in the frame before the frame containing the block unit corresponding to that cell is calculated, and the data for that block is calculated. The data for all pixels constituting the image data is replaced with the average value and output as image data, and when no cells are discarded, the input data returned to the format before quantization is output as image data as is.

[Created for]

In the present invention, compensation is performed on the receiving side when a cell is discarded in an image data transmission system in which image data encoded in blocks of a plurality of pixels is transmitted in the form of cells, for example. In the first invention shown in FIG. 1(a), compensation in the orthogonal transform coefficient domain is targeted, and for a block whose data cannot be received at all due to cell discard, DC current is applied to the corresponding block in the previous frame. The components, that is, only the upper left coefficient in the coefficient area remains as is, and the AC components, that is, all other coefficients, are set to O, and these coefficients are output to the inverse orthogonal transform unit 11 as data of the discarded block. .

Further, in the second invention shown in FIG. 1(b), compensation in the pixel area is targeted. The data of all the pixels in the corresponding block in the frame before the block whose contents have become completely unknown due to cell discard are averaged, and the average value is used as the data of all the pixels of the discarded block. It is output as image data. That is, all output data in the pixel area is constant for that block.

As described above, according to the present invention, for a block whose data has become completely unknown due to cell discard, only the DC component, that is, the average value, of the corresponding block in the frame before the frame including the block is determined. This will be outputted to all the pixels constituting the block, and the inside of the block will have no pattern and will be displayed in --like colors on the display screen.

〔Example〕

FIG. 2 shows an embodiment of the Φ concept of the invention with a coefficient N. FIG. 5A shows that input data from the transmission path is decoded at 16 on the receiving side, subjected to inverse orthogonal transformation at 17, and output as image data. Same figure (b)
shows an example of the coefficient domain after normal decoding when cells are not discarded.
A ×2 coefficient region is shown. Here, the upper leftmost coefficient represents the DC component, and all other coefficients represent the AC component. The same figure (c
) indicates the coefficient area after decoding processing when cell discard occurs; in the present invention, only the DC component (indicated by dc') of the corresponding block in the previous frame is left as is, and all The AC portion is cleared to O.

FIG. 3 explains the concept of the embodiment of the present invention in the pixel area. FIG. 5A shows that input data from the transmission path to the receiving section is decoded at 18 and output as image data.

Figure (b) shows the pixel area after normal decoding when no cell discard occurs, and the data for each pixel,
For example, density data is output as is. Figure (c) shows the pixel area after decoding when cell discard occurs, and the average value of the pixel area data (indicated by a dash) of the corresponding block in the previous frame is This indicates that the data is output as data for all pixels in the image.

FIG. 4 is a block diagram of the overall configuration of an embodiment of an image data transmission system in the coefficient domain. In the figure, the transmitting side includes a DCT unit 20SDCT that performs discrete cosine transform (DCT), which is a type of orthogonal transform, on input image data.
A subtracter 22 that takes the difference between the output S of the unit 20 and the corresponding block data S in the previous frame stored in the frame memory 21, and quantization that quantizes the output S of the subtractor 22. Inverse quantizer 24 returns the output of the quantizer 23 to the pre-quantization format S (2) An adder 25 that adds S to S, and a leak coefficient multiplier 26 that multiplies the output (S) of the adder 25 by a leak coefficient α and outputs it to the frame memory 21.

Also, on the receiving side, the signal ■S input via the transmission path
An inverse quantizer 27 that returns the quantized input data to its original format ■R, and an addition that takes the sum of its output ■R and the block data ■R in the previous frame stored in the frame memory 28 29, a discard compensating section (A) 30 corresponding to the discard compensating means 12 in FIG. and a leak coefficient multiplier 32 that multiplies the output of the discard compensation unit (A) 30 by the leak coefficient α and outputs it to the frame memory 28.
Consists of.

Here, the discrete cosine transform (DCT) uses a transformation matrix created from a cosine function, and it required a multiplier for calculation, making it difficult to perform high-speed calculations, but with the development of high-speed signal processing processors, stationary It is now widely used for semi-video transmission such as image transmission and video conference signals.

FIG. 4 shows an embodiment of the present invention using an interframe coding method. For example, on the transmitting side, block data S in the frame to be currently transmitted and block data S in the previously transmitted frame are The difference, that is, the difference between frames is ■S
It is quantized and, for example, Huffman encoded, and output on a transmission path. On the receiving side, the difference from the transmission path ■
By receiving R and calculating the sum with the block data ■R in the previous frame, the block data ■R in the current frame is obtained. And on the sending side, the difference ■S
The adder 25 calculates the sum of the block data ■S in the previous frame and multiplies it by the leakage coefficient α.
It is stored in the frame memory 21 in order to obtain the inter-frame difference for the next frame. In the receiving section as well, the current block data (1) R is similarly multiplied by the leakage coefficient α and then stored in the frame memory 28.

The leakage coefficient α is used, for example, to attenuate the effect of cell discard in a short time even if cell discard occurs. For example, the difference D1 is input on the receiving side, and the block data FM of the previous frame stored in the frame memory 28
, and the sum (DB + FMa) is multiplied by the leakage coefficient α, and the block data for the current frame expressed by the following equation becomes the content FM1 of the frame memory 28.

FMI = (DI + FM+) α = D, α + FMO α Next, the difference D2 which is the block data between the next frames
When input from the transmission line, the contents of the frame memory 28 become as follows.

F Mz = (Dz + F Ml ) α= 02
tx+l), α''+FM6α2 When block data D3 between the next frames is further input, the contents of the frame memory 28 are given by the following equation.

FM2 = (Ds +F'Mz) α=D2 a
+Dz α” +1), a”+FMOα3 In this way, for example, the prediction error D when cell discard occurs
The influence of + on the entire image is α7 after inputting n frames.
attenuates to Therefore, by setting α smaller than 1,
The effect can be reduced to almost zero in a short period of time.

FIG. 5 is an example of coefficient data in the coefficient domain in the image data transmission system of FIG. 4. In the same figure (a)
indicates coefficient data on the transmitting side, and indicates block data S which is encoded as an interframe signal by subtracting block data S in the previous frame from block data S in the current frame. FIG. 6(b) shows block data when frame discard occurs on the receiving side, and the received data ■R is completely unknown.

In this case, the discard compensator (A) 30 leaves only the DC component of the coefficients of the block data ■R in the previous frame, and sets the other coefficients, that is, all the AC components to 0, so that the current frame The data is output to the inverse DCT unit 31 as block data ■R. Figure (C) shows conventional processing on the receiving side when the present invention is not used, in which block data ■R in the previous frame is output as is to the inverse DCT unit 31 as block data ■R in the current frame. .

FIG. 6 is a block diagram of an overall configuration of an embodiment of an image data transmission system in a pixel area. Comparing this figure with FIG. 4 in the coefficient domain, the configuration is completely the same as that in FIG. 4 except that the DCT section 20 that performs discrete cosine transform as orthogonal transform and the inverse DCT section 31 that performs inverse orthogonal transform are not present. . Its operation is exactly the same as that shown in FIG. 4, except that pixel data itself, for example, pixel density data, is encoded as is in the pixel area without orthogonal transformation.

FIG. 7 is an example of block data in the image data transmission system in the pixel area of FIG.

The meaning of this diagram is exactly the same as that of FIG. 5 except that each data is the data itself of each pixel in the pixel area. Figure (a) shows the data on the sending side;
b) shows the process of the present invention, in which when cell discard occurs and the block data ■R in the current frame is unknown, the average value of data for all pixels in the block data ■R in the previous frame is determined. The average value is taken as the data for all pixels of block data ①R of the current frame. On the other hand, in FIG. 2C, which shows conventional processing, the block data ■R in the previous frame is used as it is as the block data ■R in the current frame. For example, if data 0 represents black and data 255 represents white, in the present invention, instead of a pattern of half black and half white, the color for data 127 that is the average of these, for example gray, is used for the discarded block. will be output for.

Figure 8 shows the discard compensation section (A) 30 on the receiving side in Figure 4.
3 is a flowchart showing an example of processing. When the process starts in the same figure, it is first determined in step 34 whether or not cell discard has occurred, and if cell discard has occurred, in step 35 the AC coefficient in the coefficient area of the corresponding block in the previous frame is determined. If all O's are cleared and the process ends, and if no cells are discarded in step 34, adder 2
The process is terminated in order to output the block data ■R in the current frame as the output of step 9 as is.

FIG. 9 is a flowchart of a processing example of the discard compensation section (B) 33 in FIG. In the figure, when the process starts, it is first determined in step 36 whether or not cell discard has occurred. If cell discard occurs, in step 37, the DC component is separated from the data in the pixel area of the corresponding block of the previous frame.1. That is, the average value of data for all pixels in the block is taken, and in step 38, the AC component is cleared to 0, that is, the average value is assigned as data for each pixel, and the process ends. If it is determined in step 36 that no cells are discarded, the input data from the adder 29 is output as is without any processing.

Note that although the example above has been explained using an area with a 2×2 pixel count and using interframe encoding as the encoding method, it is obvious that the number of pixels in a block is not limited to 2×2. It goes without saying that the encoding method is not limited to interframe encoding, but may also be intraframe encoding.

〔Effect of the invention〕

As explained in detail above, according to the present invention, even if cells are discarded, the block pattern in the previous frame is not left as is and is expressed in a --like color, so that the effect of cell discard on image quality is reduced. can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the principle of the present invention. FIG. 2 is a diagram showing the concept of an embodiment of the present invention in the coefficient domain. FIG. 3 is a diagram showing the concept of an embodiment of the present invention in the pixel domain. is a block diagram showing the overall configuration of an embodiment of the image data transmission system in the coefficient domain, FIG. 5 is a diagram showing an embodiment of block data in the image data transmission system of FIG. 4, and FIG. A block diagram showing the overall configuration of an embodiment of the transmission system, FIG. 7 is a diagram showing an embodiment of block data in the image data transmission system of FIG. 6, and FIG. 8 is a processing example of the discard compensation unit (A). 9 is a flowchart of a processing example of the discard compensation unit (B), FIG. 10 is a block diagram showing the overall configuration of an image data transmission system using orthonormal transformation, and FIG. 11 is orthogonal transformation of image data. It is a figure which shows the subsequent transformation coefficient area|region. 20... Discrete cosine transform (DCT) unit, 21.28... Frame memory, 22... Subtractor, 25.29... Adder, 26.32... Leak coefficient (α) multiplier , 30...
Discard compensation section (A), 31... inverse discrete cosine transform (DCT) section, 33... discard compensation section (B).

Claims (1)

[Claims] 1) Orthogonally transform input image data using a plurality of pixels as a block, encode the coefficients in the orthogonal transform coefficient area, transmit it in units of cells, and inverse orthogonally transform the received data to the receiving side. In an image data transmission system having an inverse orthogonal transform unit (11) that outputs image data, on the receiving side of the image data transmission system, the presence or absence of cell discard is detected, and when there is discard, a block corresponding to the discarded cell is installed. An inverse orthogonal transform unit (11) clears all the coefficients representing AC components to 0 after decoding the data of the coefficient domain of the block corresponding to the block in a frame temporally one frame earlier than the frame containing the block. A cell discard compensation image decoding system comprising a discard compensating means (12) for outputting a decoded input as is to an inverse orthogonal transform unit (11) when there is no cell discard. 2) In an image data transmission system in which input image data is encoded in the pixel area using multiple pixels as blocks and transmitted in cell units, the receiving side of the image data transmission system detects whether or not cells are discarded and detects whether or not cells have been discarded. Sometimes, the average value of the decoded data for all pixels constituting the block corresponding to the block is determined in a frame that is one frame before the frame that includes the block corresponding to the discarded cell, and the block is constructed. A cell discard compensation image decoding system characterized by having a discard compensating means (13) which replaces data for all pixels with the average value and outputs the data, and outputs the decoded input as is when there is no cell discard. .