JPH07177521A - Image decoder - Google Patents

Abstract

PURPOSE:To reduce the block distortion of a pixel/image after decoding. CONSTITUTION:The decoder consists of a variable length decoding section 1 decoding a coded picture signal 10 to generate a decoded picture signal, an inverse quantization section 2 using inverse quantization data obtained from the variable length decoding section 1 to generate a frequency component signal from the decoded picture signal, an inverse orthogonal conversion section 3 applying inverse orthogonal transformation to the frequency component signal to generate a pixel/picture signal, a motion compensation decoding section 4 compensating a moving pixel/picture signal based on a motion vector, a control data extract section 7 extracting required data among control data 12 generated by the variable length decoding section 1, a switching signal generating section 5 generating a switching signal 13 based on extracted control data outputted from the control data extract section 7, and a variable filter section 6 correcting the pixel/picture signal outputted from the motion compensation decoding section 4 to generate a pixel/picture signal whose block distortion is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image decoding apparatus capable of reducing block distortion of a decoded pixel image.

[0002]

2. Description of the Related Art Usually, image information has a large amount of data, and especially natural images and moving images have a very large amount of data. Therefore, various data compression techniques have been disclosed for efficiently transmitting or storing such image information. MPEG (Moving Picture)
Although it is being studied by international standardization organizations such as e coding Experts Group), motion compensation prediction and DCT (Discrea) are one of the data compression techniques.
There is a technology that combines t Cosine Transformation (discrete cosine transformation). As such a transform encoded data compression technique, there is a method in which a pixel image to be data compressed is first divided into blocks and the transform encoded data is compressed for each divided block. FIG. 3 is a block diagram of a general image coding apparatus.
The image encoding device shown in this figure is based on the pixel image signal 3
0 is subjected to the motion-compensated prediction, divided into blocks, the transformed encoded data is compressed, and the encoded image signal 10 is output. The image coding apparatus shown in FIG. 3 includes the preprocessing unit 21, the motion compensation prediction unit 22, the orthogonal transformation unit 23, the quantization unit 24, and the variable length coding unit 25. The pre-processing unit 21 limits the frequency band of the pixel image signal 30 so as to be suitable for compression, and removes noise. The motion compensation prediction unit 22 detects a motion vector between frames and reduces the difference value in the time axis direction to be transmitted to the next stage based on the motion vector. The orthogonal transformation unit 23 divides the pixel image signal into blocks and performs orthogonal transformation such as two-dimensional Fourier transform and two-dimensional DCT. The quantization unit 24 generates a data-compressed coded image signal using a quantization table or the like. The variable length coding unit 25 further compresses the coded image signal to generate a final coded image signal 10. FIG. 4 is a block diagram of a general image decoding apparatus. The image decoding apparatus shown in this figure obtains a decoded pixel image signal 31 corresponding to the pixel image signal 30 from the coded image signal 10 generated by the image coding apparatus of FIG. is there. The image decoding apparatus shown in FIG. 4 includes a variable length decoding unit 1, an inverse quantization unit 2, an inverse orthogonal transform unit 3, and a motion compensation decoding unit 4. The variable length decoding unit 1 decodes the decoded image signal using a variable length decoding table or the like. The dequantization unit 2 uses the dequantized data obtained from the variable length decoding unit 1 to generate a frequency component signal from the decoded image signal. The inverse orthogonal transform unit 3 performs an inverse orthogonal transform on the frequency component signal to generate a pixel image signal. The motion compensation decoding unit 4 performs motion compensation based on the motion vector on the decoded pixel image signal 3
1 is generated. The decoded pixel image signal 31 corresponds to the pixel image signal 30 of FIG. The image encoding device and the image decoding device described above can significantly compress data. However, the block division conversion coding data compression technique described above has a problem that block distortion occurs in a pixel image after decoding. Note that this block distortion causes a difference in image quality between the divided blocks, resulting in an unsightly display image state such as a tiled pattern or a zigzag pattern.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and decodes an image capable of reducing block distortion that occurs when an input image signal is orthogonally transformed in units of blocks and encoded. It is an object of the present invention to provide a chemical conversion device.

[0004]

In order to achieve the above object, a decoding means for motion-compensating and decoding a coded image signal to generate a pixel image signal, and a quantization width data generated by the decoding means are used. , Filter means for correcting the high frequency component of the pixel image signal.

[0005]

With the above arrangement, when the quantization width data is large, the extent to which the high frequency component of the filter means is removed is increased. Further, when the quantization width data is small, the degree of removing the high frequency component of the filter means is reduced, or the filter means is not passed.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image decoding apparatus according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of an image decoding apparatus according to the present invention. As shown in the figure, 1 is a variable length decoding unit that decodes the input coded image signal 10 to generate a decoded image signal. Two
Is a dequantization unit that uses the dequantized data obtained from the variable length decoding unit 1 to generate a frequency component signal from the decoded image signal. An inverse orthogonal transform unit 3 performs an inverse orthogonal transform on the frequency component signal to generate a pixel image signal. Reference numeral 4 is a motion compensation decoding unit that compensates a moving pixel image signal based on the motion vector obtained from the variable length decoding unit 1. Reference numeral 7 denotes required data from the control data 12 generated by the variable length decoding unit 1, for example, quantization width data for controlling the compression bit rate corresponding to the state of the original image, motion vector data, It is a control data extraction unit that extracts the encoding mode data. 5
Is a switching signal generation unit that generates a switching signal 13 based on extraction control data output from the control data extraction unit 7, such as quantization width data, motion vector data, and coding mode data. Reference numeral 6 denotes a pixel image signal in which the block distortion is reduced by switching the correction level of the high frequency component of the pixel image signal output from the motion compensation decoding unit 4 in accordance with the switching signal 13 supplied from the switching signal generation unit 5. 11 is a variable filter unit for generating 11.

The operation of the image decoding apparatus according to the present invention will be described with reference to FIG. Incidentally, the same parts as the operations described in the conventional example will be omitted. From the control data 12 generated by the variable length decoding unit 1, the control data extraction unit 7 encodes, for example, quantization width data for controlling the compression bit rate according to the state of the original image, motion vector data, and encoding. The mode data is extracted and supplied to the switching signal generator 5 as extraction control data. The switching signal generation unit 5 evaluates the received extraction control data by using, for example, a plurality of data conversion tables or by calculation, and switches the switching signal 13, for example, the switching signal A, the switching signal B, and the switching signal. C is generated and supplied to the variable filter unit 6. More specifically, when the quantization width data is large and the motion vector data is zero or small as compared with it, the switching signal to be generated is composed of the quantization width data. When the quantization width data and the motion vector data are about the same, the switching signal to be generated is the data obtained by the arithmetic mean of the quantization width data and the motion vector data, for example, by using a conversion table or by calculation. . Further, when the quantization width data is zero or small and the motion vector data is large in comparison thereto, the switching signal to be generated is composed of the motion vector data. The variable filter unit 6 that receives the switching signal 13
Three low-pass filters A corresponding to the switching signal A, the switching signal B, and the switching signal C that form the variable filter unit 6, a low-pass filter B, and a low-pass filter C.
And the high-frequency component of the pixel image signal output by the motion compensation decoding unit 4 is set to one of the characteristics of the low-pass filter A, the low-pass filter B, and the low-pass filter C that have been switched and selected. Remove accordingly. The type of switching signal 13 and the number of low-pass filters corresponding thereto are not limited to the above three.

[0008]

As described above, the present invention provides an image decoding apparatus capable of reducing block distortion that occurs when an input image signal is orthogonally transformed in units of blocks and encoded. Therefore, firstly, a conventional tiled or zigzag unsightly display image state occurs in the pixel image after decoding the image signal subjected to the significant data compression using the image decoding device. Block distortion was seen, but it can be prevented from occurring. Secondly, since a low-pass filter is not applied to a still image and an image with little motion, it is possible to decode a high-definition image with no loss of high-frequency components. In conclusion, there is a merit that image data that has been significantly compressed can be reproduced in a high image quality state.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an image decoding apparatus according to the present invention.

FIG. 2 is a relationship table between a switching signal generated by a switching signal generation unit of the image decoding apparatus according to the present invention and control data supplied.

FIG. 3 is a block diagram of a general image encoding device.

FIG. 4 is a block diagram of a general image decoding apparatus.

[Explanation of symbols]

 1 Variable Length Decoding Section 2 Inverse Quantization Section 3 Inverse Orthogonal Transformation Section 4 Motion Compensation Decoding Section 5 Switching Signal Generation Section 6 Variable Filter Section 7 Control Data Extraction Section 10 Coded Image Signal 11 Pixel Image Signal 12 Control Data 13 Switching Signal 21 Pre-processing unit 22 Motion compensation prediction unit 23 Orthogonal transformation unit 24 Quantization unit 25 Variable length coding unit 30 Pixel image signal 31 Decoded pixel image signal

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04N 11/04 B 7337-5C H04N 7/133 Z

Claims (9)

[Claims] 1. A high-frequency component of the pixel image signal is corrected on the basis of decoding means for motion-compensating and decoding the encoded image signal to generate a pixel image signal, and quantization width data generated by the decoding means. An image decoding device comprising: a filter means. 2. A decoding unit for motion-compensating and decoding an encoded image signal to generate a pixel image signal, and a filter for correcting a high frequency component of the pixel image signal based on motion vector data generated by the decoding unit. An image decoding apparatus comprising: 3. Decoding means for motion-compensating and decoding a coded image signal to generate a pixel image signal, and quantization width data and motion vector data generated by the decoding means,
An image decoding apparatus comprising: a filter unit that corrects a high frequency component of the pixel image signal. 4. A frequency component from the decoded image signal using a variable length decoding unit for decoding a coded image signal to generate a decoded image signal, and dequantized data obtained from the variable length decoding unit. An inverse quantization unit that generates a signal, an inverse orthogonal transformation unit that performs an inverse orthogonal transform on the frequency component signal to generate a pixel image signal, and a motion compensation that compensates a moving pixel image signal based on a motion vector. A decoding unit, a control data extraction unit that extracts required data from the control data generated by the variable length decoding unit, and a switching signal generation that generates a switching signal based on the extraction control data output by the control data extraction unit And a variable filter unit that corrects a pixel image signal output from the motion compensation decoding unit. 5. The image decoding apparatus according to claim 4, wherein the extraction control data output from the control data extraction unit is quantization width data and encoding mode data. 6. The image decoding apparatus according to claim 4, wherein the extraction control data output from the control data extraction unit is motion vector data and coding mode data. 7. The image decoding apparatus according to claim 4, wherein the extraction control data output from the control data extraction unit is quantization width data, motion vector data, and encoding mode data. 8. The image decoding apparatus according to claim 4, wherein the variable filter section is composed of a plurality of low-pass filters. 9. The image decoding apparatus according to claim 4, wherein the switching signal generation unit is composed of a plurality of data conversion tables.