JPH0549022A - Picture coder - Google Patents

Abstract

PURPOSE:To provide the picture coder in which no remarkable deterioration in picture quality is caused even when information is missing on the way of transmission by eliminating block distortion and deterioration in the picture quality. CONSTITUTION:The picture coder having a frame memory 22 storing a picture signal is provided with a delay section 10 delaying an inputted picture signal by a prescribed time, a pre-processing section 11 pre-processing the picture signal delayed by the delay section 10, a pre-processing section 12 pre-processing the picture signal read by the pre-processing section 11, a comparison section 13 comparing the picture signal pre-processed by the pre-processing section 11 and the picture signal pre-processed by the pre-processing section 12 and outputting a picture error signal, and an error coding section 14 coding the picture error signal outputted from the comparison section 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image coding apparatus for reducing the amount of information contained in a moving image and compressing and coding the image in a form suitable for transmission through a communication line.

[0002]

2. Description of the Related Art In recent years, digital public networks (hereinafter referred to as ISD
The demand for an image communication service as a new communication service is increasing due to the popularization of (N.) and the progress of image coding technology, and it is being put to practical use in some parts such as videophones and videoconference systems. In addition, new communication networks represented by broadband ISDN are being actively studied with the aim of providing more advanced services.

Generally, the amount of information contained in an image is enormous, and a large-capacity transmission line is required to transmit an image signal as it is through a communication line. Considering communication costs, such image transmission is not possible. It is realistic. Therefore, it is considered to effectively use the redundancy included in the image signal to reduce the amount of information.

Although various methods have been studied as image coding methods, the motion compensation interframe predictive orthogonal transform coding method is currently most widely used. FIG. 4 shows a schematic configuration of an image coding apparatus using the motion compensation inter-frame prediction orthogonal transform coding method.

The image coding apparatus shown in FIG.
Orthogonal transformation unit 31, coding control unit 32, quantization unit 33, dequantization unit 34, inverse orthogonal transformation unit 35, addition unit 36, frame memory unit 37.
And a motion compensation inter-frame prediction unit 38.

The motion-compensated inter-frame prediction unit (hereinafter referred to as the prediction unit) 38 and the difference calculation unit 30 perform motion-compensated inter-frame prediction for each image frame based on the input image signal.

The prediction unit 38 uses a frame memory unit (hereinafter referred to as a memory unit) to detect motion in motion compensation.
The image signal of one frame before stored in 37 and the input image signal are divided into blocks of a certain size, and it is detected from which part of the image signal of one frame before the block of the input image signal has moved. .. Then, based on the detection result, the image signal encoded one frame before stored in the memory unit 37 is output as a prediction value.

The difference calculation section 30 calculates the difference between the predicted value output from the memory section 37 and the input image signal, and outputs a prediction error signal as a result of interframe predictive coding.

The orthogonal transformation unit 31 orthogonally transforms the prediction error signal, and the quantization unit 33 uses the obtained orthogonal transformation coefficient to the coding control unit.
Information is compressed by quantization with a predetermined quantization step size under the control of 32.

The quantizer 33 outputs the quantized transform coefficient to the outside as a result of encoding, and also outputs it to the inverse quantizer 34.

The inverse quantizing unit 34 inversely quantizes the transform coefficient quantized by the quantizing unit 33 and outputs the transform coefficient, and the inverse orthogonal transform unit 35 performs inverse orthogonal transform on the transform coefficient to obtain a prediction error signal. To calculate.

The adder unit 36 adds the prediction value read from the memory unit 37 to the prediction error signal output from the inverse orthogonal transform unit 35 to generate an image signal. The generated image signal is
It is stored in the memory unit 37 and used for inter-frame prediction of the image signal of the next frame.

The input image signal is coded by such a loop structure and sent to the communication line.

[0014]

In the above-described conventional image coding apparatus, the screen is divided into several blocks and processed in order to efficiently perform the operation for motion detection or orthogonal transform of motion compensation prediction. When quantizing the result of the orthogonal transformation, the quantization step size is controlled based on the generated code amount and transmission capacity, so the quantization condition differs for each divided block, As a result, when a coded image is viewed on the entire screen, there is a problem that block distortion and screen roughness vary from block to block and the image quality deteriorates. Further, when quantizing the result of the orthogonal transformation, a certain degree of error is allowed to reduce the amount of information, and there is a problem that the image quality is deteriorated due to the error. Further, since all the outputs of the quantizing unit 33 are subjected to inverse quantization and inverse orthogonal transform, locally decoded and stored in the memory unit 37 and used for interframe predictive coding, the information on the communication line is When the loss occurs, there is a problem that the inter-frame predictive coding does not function normally and the image quality deteriorates remarkably.

In view of the above-mentioned problems in the conventional image coding apparatus, the present invention is an image code for coding an image signal so that block distortion and deterioration of the image can be avoided even if the image information is lost during transmission. To provide a rectification device.

[0016]

SUMMARY OF THE INVENTION The present invention is an image coding apparatus having a memory for storing a first image signal, the delay unit delaying an input second image signal by a predetermined time, and a delay unit. First processing means for preprocessing the second image signal delayed by the means, second processing means for preprocessing the first image signal read from the memory, and first processing preprocessed by the first processing means. Comparing the image signal and the second image signal pre-processed by the second processing means to output an image error signal, and encoding means for encoding the image error signal output from the comparing means. Image coding apparatus.

[0017]

The delay means delays the input image signal by a predetermined time, the first processing means pre-processes the second image signal delayed by the delay means, and the second processing means reads the second image signal from the memory. One image signal is pre-processed, and the comparison means outputs the image error signal by comparing the second image signal pre-processed by the first processing means and the first image signal pre-processed by the second processing means, and outputs the code. The encoding means encodes the image error signal output from the comparing means.

[0018]

Embodiments of the image coding apparatus of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the image coding apparatus of the present invention.

The image coding apparatus shown in FIG. 1 includes a delay unit 10 which is a delay unit, a preprocessing unit 11 which is a first preprocessing unit, a preprocessing unit 12 which is a second preprocessing unit, and a comparison unit which is a comparison unit. 13 and an error encoding unit 14, which is an encoding unit, a difference calculation unit 15, an orthogonal transformation unit 16, an encoding control unit 17, a quantization unit 18, and an inverse quantization unit 1.
9, an inverse orthogonal transformation unit 20, an addition unit 21, a frame memory unit 22, and a motion compensation inter-frame prediction unit 23.

Next, the operation of each of the above components will be described.

The main part of the image coding apparatus shown in FIG. 1 is a delay part.
It includes a preprocessing unit 11, a preprocessing unit 11, a preprocessing unit 12, a comparison unit 13, and an error coding unit 14.

The delay unit 10 delays the input image signal, which is the second image signal, by the time corresponding to the delay caused in the process of the encoding process, and outputs the result to the preprocessing unit 11.

The pre-processing unit 11 performs pre-processing such as filter processing and enhancement processing on all or part of the image signal which is the second image signal delayed by the delay unit 10.

The pre-processing unit 12 performs pre-processing such as filter processing and enhancement processing on all or part of the image signal which is the first image signal read from the frame memory unit 22. For example, since block distortion occurs near the block boundary, local enhancement processing is performed.

The comparison unit 13 compares the image signals preprocessed by the preprocessing units 11 and 12 to detect how much the coded image is deteriorated. More specifically, near the boundary where block distortion occurs, the difference between the pre-processed input image signal and the coded image signal is calculated, and the result is quantized. To detect. For the deterioration of the image quality due to the difference in the screen roughness of each block due to the difference in the quantization step size at the time of quantization and the deterioration of the image quality due to the quantization error, the input image signal and the encoding The difference calculation from the image signal is performed in pixel units, and the error is accumulated in block units to detect which block has a large error.

The error coding unit 14 transform-codes the above-mentioned detection result and then outputs it as an image error signal to the outside.

The motion-compensated inter-frame prediction unit 23 and the difference calculation unit 15 perform motion-compensated inter-frame prediction for each image frame based on the input image signal.

The motion-compensated inter-frame prediction unit 23 divides the image signal of one frame before stored in the frame memory unit 22 and the input image signal into blocks of a predetermined size as motion detection in motion compensation, It is detected from which part of the image signal of the preceding frame the block of the input image signal has moved. Then, based on the detection result, the image signal coded one frame before stored in the frame memory unit 22 is output as a prediction value.

The difference calculator 15 calculates the difference between the predicted value output from the frame memory 22 and the input image signal, and outputs a prediction error signal as a result of interframe predictive coding.

The orthogonal transformation unit 16 orthogonally transforms the prediction error signal output from the difference calculation unit 15, and the quantization unit 18 encodes the orthogonal transformation coefficient obtained by the orthogonal transformation in the orthogonal transformation unit 16 into the coding control unit. Under the control of 17, the information is compressed by quantizing it into a predetermined quantization step size.

The quantizer 18 outputs the quantized transform coefficient to the outside as a result of encoding, and also the inverse quantizer 19
Also send.

The inverse quantizing unit 19 inversely quantizes the transform coefficient quantized by the quantizing unit 18 and outputs the transform coefficient, and the inverse orthogonal transform unit 20 outputs the transform coefficient output from the inverse quantizing unit 19. Inverse orthogonal transformation is performed and a prediction error signal is output.

The adder 21 adds the prediction value read from the frame memory 22 to the prediction error signal output from the inverse orthogonal transformer 20 to generate an image signal. The generated image signal is stored in the frame memory unit 22 and used for inter-frame prediction of the image signal of the next frame.

Next, the above processing will be described with reference to FIG.

The input image signal 24 is divided into blocks 25,
Encoded in the encoding loop, quantizer 18 (see FIG. 1)
Is output to the outside and is stored in the frame memory unit 22 (see FIG. 1) as the encoded image signal 26. The encoded image signal 26 is the same as the image signal restored by the device on the other side unless information is lost on the transmission path, and block distortion or the like has occurred.

The encoded image signal 26 is an image signal 27 in which block distortion and the like are emphasized by the preprocessing unit 12 (see FIG. 1).
Therefore, the comparison unit 13 (see FIG. 1) compares the image signal 27 with the input image signal 24. A block distortion detection result 28 is obtained from the comparison result, and an error accumulation result 29 for each block is obtained. The shaded areas of the accumulated result 29 represent different errors. These comparison results are encoded by the error encoding unit 14 (see FIG. 1) and output to the outside.

The processing operation of FIG. 2 will be described in detail with reference to the flowchart of FIG.

First, the operation of the non-priority cell will be described.

An image is input (step S1), the input image signal is delayed by a time corresponding to the delay caused in the process of encoding (step S2), and the delayed image signal and the frame memory unit 22 are read. The pre-processing such as filter processing and enhancement processing is performed on all or part of the processed image signal (step S3) to detect the occurrence of block distortion (step S4), and the polarity of the pre-processed image signal is detected. Comparison is performed (step S5), it is detected whether or not the polarities are the same (step S6), and if YES in step S6, it is determined whether the block distortion is equal to or smaller than the threshold value V _{th (1).} (Step S7), and if YES in step S7, the encoding is not performed. If NO in step S7, the boundary error is quantized (step S8), and the non-priority cell is transmitted.

On the other hand, if NO in step S6, it is determined whether the block distortion is equal to or smaller than the threshold value V _{th (2)} (step S9), and the step S9 is executed.
If YES at step, encoding is not performed. If NO in step S9, the boundary error is quantized (step S10), and the non-priority cell is transmitted.

In the nest step S3, with respect to the deterioration of the image quality due to the difference in the screen roughness for each block due to the difference in the quantization step size at the time of quantization and the deterioration in the image quality due to the quantization error, , The difference calculation between the input image signal and the encoded image signal is performed in pixel units, the error is accumulated in block units (step S11), which block has a large error is detected (step S12), and the maximum error is detected. Is equal to or smaller than the threshold value V _{th (3)} (step S13), and if YES in step S13, the encoding is not performed. If NO in step S13, the accumulated error of each block is quantized (step S14), the block to be encoded is determined (step S15), and the non-priority cell is transmitted.

Next, the operation related to the priority cell will be described.

Motion-compensated interframe prediction is performed for each image frame based on the input image signal (step S16),
The prediction error signal is orthogonally transformed (step S17), the orthogonal transformation coefficient obtained by the orthogonal transformation is quantized into a predetermined quantization step size and information is compressed (step S18), and is output to the outside as a priority cell. Further, the transform coefficient quantized in the above step S18 is inversely quantized and the transform coefficient is output (step S19), the transform coefficient is subjected to inverse orthogonal transform and a prediction error signal is output (step S20), and the prediction error signal Frame
The prediction value read from the memory unit 22 is added to generate an image signal (step S21).

The generated image signal goes through the processes of steps S4 to S8 and S10 described above, and also goes through the processes of steps S11 to S15 described above to output non-priority cells.

As described above, the image coding apparatus according to the present embodiment not only outputs the coded image signal but also outputs the image error signal including the information related to the distortion and deterioration of the coded image. Output. Therefore, when the image signal is decoded after the image transmission, by using the image error signal, it is possible to restore a faithful image signal to the original signal (input image signal) without block distortion and deterioration of image quality.

Further, the information coded by the above-mentioned image coding apparatus can be hierarchized in two stages of the coded image signal and the image error signal, and the coded image signal has priority. If the information is lost, only the image error signal is lost even if the information is lost, and the loss of information does not affect the inter-frame prediction.

[0048]

The image coding apparatus of the present invention comprises delay means for delaying the input second image signal by a predetermined time,
First processing means for preprocessing the second image signal delayed by the delay means, second processing means for preprocessing the first image signal read from the memory, and first processing means preprocessed by the first processing means. Comparing means for comparing the one image signal and the second image signal preprocessed by the second processing means to output an image error signal, and encoding means for encoding the image error signal output from the comparing means. Therefore, it is possible to transmit an image signal without image block distortion or deterioration, and the image signal is layered into an encoded image signal and an image error signal to output the encoded image signal with priority. As a result, even when information is lost, it is possible to eliminate the influence of only the image error signal on the inter-frame prediction.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining processing in the image encoding device in FIG.

FIG. 3 is a flowchart for explaining the operation of the image coding apparatus in FIG.

FIG. 4 is a block diagram showing an example of a conventional image encoding device.

[Explanation of symbols]

 10 Delay unit 11, 12 Pre-processing unit 13 Comparison unit 14 Error coding unit 15 Difference calculation unit 16 Orthogonal transformation unit 17 Coding control unit 18 Quantization unit 19 Inverse quantization unit 20 Inverse orthogonal transformation unit 21 Addition unit 22 Frame memory Part 23 Motion compensation interframe prediction unit

Claims (1)

[Claims] 1. An image encoding apparatus having a memory for storing a first image signal, comprising: delay means for delaying an input second image signal by a predetermined time; and the delay means delayed by the delay means. First processing means for preprocessing two image signals, second processing means for preprocessing the first image signal read from the memory, and first image signal preprocessed by the first processing means And comparing means for comparing the second image signal preprocessed by the second processing means and outputting an image error signal, and encoding means for encoding the image error signal output from the comparing means. An image encoding device characterized by being provided.