JP2002199403A - Block distortion detecting method, block distortion detector, block distortion eliminating method and block distortion eliminating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a block distortion eliminating device that detects block distortion with high accuracy in the case of decoding a compression coded image so as to eliminate the block distortion, while minimizing blurring of images. SOLUTION: A block distortion detector 109 uses image data after decoding and information of motion vector to specify a block border in which block distortion takes place. The block distortion eliminating device 108 applies filtering to pixels around the block border of the image after decoding, on the basis of the result of detection by the block distortion detector 109 and eliminates block distortion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a block distortion detecting method, a block distortion detecting apparatus, a block distortion detecting method, and a block distortion detecting method for detecting and removing block distortion generated when an image compression-encoded in blocks is decoded. The present invention relates to a distortion removing device.

[0002]

2. Description of the Related Art In recent years, MPEG (Moving) has been used as a highly efficient compression coding method for images in the fields of broadcasting, communication and storage.
Picture Expert Group) method. The H.263 system is widely used. MPEG format and H.264 In the H.263 system, encoding is performed by removing redundancy in the spatial direction and the temporal direction from an image. Hereinafter, an outline of the MPEG system will be described.

[0003] First, in order to remove spatial redundancy included in image information, a discrete cosine transform (Discrete C
osine transform (hereinafter referred to as DCT) and quantization processing. That is, after the input image is divided into units called blocks of 8 × 8 pixels, the blocks are converted into coefficients (DCT coefficients) in the frequency domain by DCT. Then, quantization processing is performed on the DCT coefficient. The quantization process is performed by using both a quantization matrix having a value corresponding to each frequency in the DCT domain and a quantization step.
This is the process of dividing the coefficient. By this quantization processing, DC
A frequency component having a small T coefficient value becomes “0”. Generally, since the energy of an image signal is concentrated in a low band, a high frequency component is deleted by this processing. However, the higher the frequency of human visual characteristics, the lower the discrimination power. Therefore, if the quantization step used in the quantization process is small, the image quality deterioration due to the quantization process is less noticeable.

[0004] In order to remove temporal redundancy, motion compensation is used. In motion compensation, 16 × 16
A region closest to the reference image is selected using a macroblock of pixels as a motion compensation unit. Then, a difference value between the area and the reference image is encoded. When the movement is not so fast, the difference value is almost “0”, so that the temporal redundancy can be reduced.

In general, when the bit rate is high, that is, when the compression ratio is small, the image quality degradation is very inconspicuous in the MPEG system. However, when the bit rate is low, that is, when the compression ratio is high, image quality degradation, that is, coding noise starts to be noticeable. A typical example of the coding noise in the MPEG system is block distortion. Block distortion is a phenomenon in which the boundaries of each block appear to be clearly tiled. This occurs because the image signal in a block has only low-frequency components, and the value of the low-frequency component differs between adjacent blocks.

[0006] Unlike conventional analog noise, block distortion is greatly conspicuous as image quality degradation. Therefore, several methods for removing this have been proposed. Documents that disclose the method include, for example, JP-A-11-27558.
No. 4 publication. This publication discloses a method of converting a motion vector of a macroblock of interest into a motion vector per frame, and changing a characteristic of a filter applied to a decoded image according to the size of the converted motion vector. Have been.

[0007]

In the above conventional method,
The frequency characteristic of the low-pass filter, that is, the cutoff frequency is determined according to the magnitude of the motion vector. Then, block distortion is removed by applying a filter to the decoded image using the determined filter. At this time, the filter characteristic is determined such that the cutoff frequency becomes lower as the motion vector becomes larger. However, even if the motion vector is large, applying a filter to a region having a high frequency component causes image quality degradation.

In the above-mentioned conventional method, the amount of processing per block in detecting block distortion is constant independently of the resolution. That is, the processing amount is the same whether the video signal has a low resolution or a high resolution. For this reason, there has been a problem that the higher the resolution of the video signal, the greater the overall processing amount.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems of the prior art, and a block distortion detecting method and a block distortion eliminating image quality deterioration due to erroneous detection when removing block distortion. It is an object to provide a distortion detection device, a block distortion removal method, and a block distortion removal device.

Further, a block distortion detecting method which does not increase the processing amount in proportion to the number of pixels and can suppress an increase in the processing amount even when the video signal has a high resolution.
It is an object to provide a block distortion detecting device, a block distortion removing method, and a block distortion removing device.

[0011]

According to a first aspect of the present invention, there is provided a method for removing a block distortion, comprising the steps of: dividing an image signal into blocks each including a plurality of pixels; For the decoded image signal obtained by decoding the first and second difference values between pixels belonging to the block near the inter-block boundary, And the first
And correcting the pixel value of the pixel near the boundary between the blocks in accordance with the difference between the second difference value and the second difference value.

A block distortion detecting method according to a second aspect of the present invention is directed to a method for detecting a decoded image signal obtained by decoding an encoded signal sequence after dividing the image signal into blocks each including a plurality of pixels. Calculating a first difference value between pixels spanning the inter-block boundary and a second difference value between pixels belonging to the block near the inter-block boundary, and calculating an absolute value of the first difference value Is larger than a first threshold value and when the absolute value of the second difference value is smaller than a second threshold value, it is determined that block distortion occurs between the block boundaries, and the first And the second
It is determined that the smaller the threshold value is, the stronger block distortion is generated between the block boundaries.

In the block distortion detecting method according to the third aspect of the present invention, an image signal is divided into blocks each including a plurality of pixels and then encoded using motion compensation in a unit including at least one of the blocks. For a decoded image signal obtained by decoding a code string, a first difference between pixels that is the inter-block boundary and the inter-block / motion compensation unit boundary that is the motion compensation unit boundary. And a second difference value between pixels belonging to the block near the boundary between the blocks / motion compensation units, and the absolute value of the first difference value is larger than a first threshold value. When the absolute value of the second difference value is smaller than a second threshold value, and the motion amount in the motion compensation unit over the inter-block / motion compensation unit boundary is larger than the third threshold value. In the border When the first and second thresholds are small, and when the amount of motion in the motion compensation unit over the inter-block / motion compensation unit boundary is large, It is determined that strong block distortion is generated.

According to a fourth aspect of the present invention, there is provided the block distortion detecting method according to the third aspect, wherein the amount of motion is the maximum of the motion amounts of the adjacent motion compensation units. Value is used.

Further, the block distortion detecting method according to the invention of claim 5 of the present application provides a method for detecting a decoded image signal obtained by decoding an encoded signal sequence after dividing the image signal into blocks each including a plurality of pixels. Calculating a first difference value between pixels spanning the inter-block boundary and a second difference value between pixels belonging to the block near the inter-block boundary, and calculating the first and second difference values. When detecting the block distortion between the block boundaries using, the detection of the block distortion is performed by a detection method in which the processing amount decreases as the resolution of the decoded image signal increases, Have.

In the block distortion detecting method according to the invention of claim 6 of the present application, an image signal is divided into blocks each including a plurality of pixels and then encoded using motion compensation in a unit including at least one of the blocks. For a decoded image signal obtained by decoding a code string, a first difference between pixels that is the inter-block boundary and the inter-block / motion compensation unit boundary that is the motion compensation unit boundary. Value and a second difference value between pixels belonging to the block near the boundary between the blocks / motion compensation units, and the first and second difference values and the boundary between the blocks / motion compensation unit are calculated. When detecting block distortion at the boundary between the blocks and between the motion compensation units using the amount of motion in the straddling motion compensation unit, the larger the resolution of the decoded image signal,
The block distortion is detected by a detection method that reduces a processing amount.

According to a seventh aspect of the present invention, there is provided a block distortion detecting method according to the fifth or sixth aspect, wherein the processing amount is reduced by a pixel used for detecting the block distortion. This is performed by reducing the number.

The block distortion detecting method according to the invention of claim 8 of the present application is the block distortion detecting method according to claim 5 or 6, wherein the decrease in the processing amount is based on the intensity of detecting the block distortion. This is performed by reducing the number of steps.

According to a ninth aspect of the present invention, in the block distortion detecting method according to the sixth aspect, the processing amount is reduced when the resolution is high. The distortion detection is performed by not performing the detection.

The block distortion removing method according to the tenth aspect of the present invention is the second, third, fifth, and fifth aspects.
A method for removing block distortion detected by the block distortion detection method according to claim 6, wherein a pixel value of a pixel near the block boundary is corrected according to a result of the determination of the block distortion. It has the composition characterized by the above-mentioned.

According to a eleventh aspect of the present invention, there is provided the block distortion eliminating method according to the tenth aspect, wherein the pixel value is corrected by a filter having different characteristics depending on the intensity of the block distortion. Performed using
And a configuration characterized by the following.

According to a twelfth aspect of the present invention, in the block distortion elimination method of the tenth aspect, the pixel value is corrected by applying a predetermined filter to pixels near the boundary. After the application, the operation is performed by using the weighted average pixel value of the pixels of the decoded image and the filtered pixels in accordance with the strength of the block distortion.

Further, the block distortion detecting apparatus according to the invention of claim 13 of the present application divides an image signal into blocks composed of a plurality of pixels and then encodes the blocks using motion compensation in a unit including at least one of the blocks. A code sequence is input, and the code sequence is decoded to generate a decoded image signal.
An image decoder for extracting a motion vector used for motion compensation at the time of the decoding; a first difference value between pixels, which receives the decoded image signal as input, and spans the inter-block boundary; A second difference value between pixels belonging to the neighboring block is obtained, and the absolute value of the first difference value is larger than a first threshold value, and the absolute value of the second difference value is set to a second value. A pixel value inspector that determines that block distortion occurs at the inter-block boundary when the threshold value is smaller than the threshold value, and determines that stronger block distortion occurs as the first and second threshold values are smaller. And a configuration characterized by comprising:

Further, the block distortion detecting apparatus according to the invention of claim 14 of the present application divides an image signal into blocks composed of a plurality of pixels, and encodes the image signal using motion compensation in a unit including at least one of the blocks. A code string is input, and the code string is decoded to generate a decoded image signal.
Further, an image decoder for extracting a motion vector used for motion compensation during the decoding, and the decoded image signal as an input, the inter-block boundary, and the inter-block A first difference value between pixels spanning a boundary between motion compensation units, and a second difference value between pixels belonging to the block near the boundary between the blocks and between motion compensation units.
When the absolute value of the first difference value is larger than a first threshold value and the absolute value of the second difference value is smaller than a second threshold value, A pixel value tester that determines that block distortion occurs between boundaries between blocks and between motion compensation units, and a motion vector in the motion compensation unit that spans the boundary between blocks and between motion compensation units. When the threshold value is larger than the threshold value of 3, a motion vector tester that determines that block distortion is generated, and a final block distortion value based on the block distortion determination results of the pixel value inspector and the motion vector inspector. A block distortion determiner for determining whether or not occurrence has occurred.

According to a fifteenth aspect of the present invention, there is provided a block distortion detecting device according to the fourteenth aspect, wherein the pixel value inspector comprises the first and second pixel value inspectors.
Is smaller, the stronger the block distortion is determined to occur, and the motion vector tester determines that the stronger the amount of motion is, the stronger the block distortion is generated.

In the block distortion detecting apparatus according to the present invention, the motion amount is the maximum of the motion amounts of the adjacent motion compensation units. Using a value.

The block distortion detecting device according to the invention of claim 17 of the present application divides an image signal into blocks each including a plurality of pixels, and encodes the image signals using motion compensation in a unit including at least one of the blocks. A code string is input, and the code string is decoded to generate a decoded image signal.
An image decoder for extracting a motion vector used for motion compensation during the decoding and a resolution of the decoded image signal; and a resolution for determining to which predetermined range the resolution of the decoded image signal belongs. A decision unit, which receives the decoded image signal as input, and obtains a first difference value between pixels spanning the inter-block boundary and a second difference value between pixels belonging to the block near the inter-block boundary. When the absolute value of the first difference value is larger than a first threshold value and the absolute value of the second difference value is smaller than a second threshold value, A pixel value tester that determines that the
A motion vector inspector that determines that strong block distortion occurs at the inter-block boundary when a motion amount in a motion compensation unit over the inter-block boundary is larger than a third threshold value; And a block distortion determiner that determines the presence or absence of final block distortion from the block distortion determination result with the motion vector tester, wherein the resolution determiner determines the decoded image signal. The configuration is characterized in that as the resolution increases, the processing amount in at least one of the pixel value inspector and the motion vector inspector decreases.

The block distortion detecting device according to the invention of claim 18 of the present application divides an image signal into blocks each including a plurality of pixels, and encodes the image signals using motion compensation in a unit including at least one of the blocks. A code sequence is input, and the code sequence is decoded to generate a decoded image signal.
An image decoder for extracting a motion vector used for motion compensation during the decoding and a resolution of the decoded image signal; and a resolution for determining to which predetermined range the resolution of the decoded image signal belongs. A decision unit, which receives the decoded image signal as input, is a boundary between the blocks, and is a boundary between the motion compensation units, and a first difference value between pixels spanning a boundary between blocks and between motion compensation units; Calculating a second difference value between pixels belonging to the block near the boundary between the blocks and between motion compensation units, wherein an absolute value of the first difference value is larger than a first threshold value; A pixel value checker that determines that block distortion occurs between boundaries between the blocks and between motion compensation units when the absolute value of the difference value of 2 is smaller than a second threshold value; , Said bro A motion vector inspector that determines that block distortion occurs when the amount of motion in a motion compensation unit that extends over a boundary between motion and motion compensation units is greater than a third threshold value; A block distortion determiner for determining the presence or absence and strength of final block distortion based on a determination result of block distortion with a motion vector tester, wherein the decoded image signal is determined by the resolution determiner. , The processing amount of at least one of the pixel value inspector and the motion vector inspector is reduced as the resolution is higher.

In the block distortion detecting apparatus according to the nineteenth aspect of the present invention, in the block distortion detecting apparatus according to the seventeenth or eighteenth aspect, the reduction in the processing amount is based on the number of pixels used for detecting the block distortion. It has a configuration characterized by performing by reducing the number.

In the block distortion detecting apparatus according to the present invention, the decrease in the processing amount may be based on the number of steps of the intensity for detecting the block distortion. Is performed by reducing the number of times.

[0031] In the block distortion detecting apparatus according to the present invention, the decrease in the processing amount may be such that the motion is reduced when the resolution is high. The detection is performed by not performing the detection of the block distortion based on the amount.

A block distortion removing apparatus according to a twenty-second aspect of the present invention provides a block distortion detecting apparatus according to any one of the thirteenth, fourteenth, seventeenth, and eighteenth aspects. An apparatus for removing distortion, wherein the decoded video signal and the determination result of the block distortion are input, and according to the determination result of the block distortion, a pixel of a pixel near the boundary of the decoded video signal is input. It has a configuration characterized by comprising a block distortion remover for correcting a value.

According to a twenty-third aspect of the present invention, in the block distortion elimination apparatus according to the twenty-second aspect, the correction of the pixel value is performed by a filter having different characteristics depending on the intensity of the block distortion. Performed using
And a configuration characterized by the following.

According to a twenty-fourth aspect of the present invention, in the block distortion elimination apparatus according to the twenty-second aspect, the pixel value is corrected by applying a predetermined filter to pixels near the boundary. After the application, the operation is performed by using the weighted average pixel value of the pixels of the decoded image and the filtered pixels in accordance with the strength of the block distortion.

[0035]

Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, it is assumed that the compression code string of the image is generated by the MPEG-2 method.

(Embodiment 1) The embodiment 1 corresponds to the inventions of claims 1 to 4, 10 to 16, 22, and 23. FIG. 1 is a block diagram of a block distortion detecting method according to a first embodiment of the present invention, a block distortion detecting device using the block distortion removing method, and an MPEG-2 decoder having the block distortion removing device. In the figure, reference numeral 102 denotes a variable length decoder for decoding an MPEG-2 video code string which is a variable length code; 103, an inverse quantizer for performing inverse quantization of the decoded variable length code; DCT that performs inverse DCT processing on the output of the transformer 103
106, a motion compensator for performing motion compensation on the output of the variable length decoder 102; 105, an adder for adding the output of the inverse DCT unit 104 and the output of the motion compensator 106;
Reference numeral 7 denotes an image memory for temporarily storing decoded image data. Reference numeral 101 denotes a variable-length decoder 102, an inverse quantizer 103, an inverse DCT unit 104, an adder 105, a motion compensator 106, and an image memory 107. MPEG-2 video decoder.

Reference numeral 109 denotes a block distortion detector for detecting the presence or absence of block distortion using the output of the image memory 107 and the output of the variable length decoder 102 in the MPEG-2 video decoder 101, and 108 denotes a block distortion detector A block distortion remover that removes block distortion using the output of the block 109. The block distortion detector 109 corresponds to a block distortion detector that detects block distortion based on the block distortion detection method of the present invention. The block 108 corresponds to a block distortion removing device that removes block distortion based on the block distortion removing method of the present invention.

Next, the operation will be described. Here, a case will be described in which inter-frame encoded data is decoded. The MPEG-2 video code string is first input to the variable length decoder 102. Variable length decoder 102
Decodes a variable-length code of an input code string and extracts quantized DCT coefficients and parameters such as a motion vector and a quantization scale used in encoding. The quantized DCT coefficients obtained by the variable length decoder 102 are input to the inverse quantizer 103 in the order of the macroblock. The inverse quantizer 103 performs inverse quantization of the DCT coefficient quantized for each block included in the macroblock using the quantization scale and the quantization matrix obtained by the variable length decoder 102, Obtain a DCT coefficient block. Then, the DCT coefficient block is input to the inverse DCT unit 104.
The inverse DCT unit 104 performs inverse DCT on the DCT coefficient block to obtain a pixel block. Inverse DCT unit 104
Are input to the adder 105.

On the other hand, a motion vector is input from the variable length decoder 102 to the motion compensator 106. Where MP
In the EG-2 system, motion compensation is performed on a macroblock basis. Then, the motion compensator 106 includes an image memory 107
, The reference image obtained using the motion vector is also obtained. Here, it is assumed that the image memory 107 stores image data of a frame that has already been decoded. This reference image is output to the adder 105. Therefore, the pixel block is input from the inverse DCT unit 104 and the reference image is input from the motion compensator 106 to the adder 105.
The adder 105 adds these, and stores the result in the image memory 107 as decoded image data. The operation so far is the same as the operation of a general MPEG-2 video decoder.

Next, the operation of the block distortion detector 109 according to the first embodiment will be described. FIG. 2 is a block diagram showing the internal configuration of the block distortion detector 109. As shown in FIG. 2, the block distortion detector 109 is a pixel value inspector 201 for inspecting whether or not block distortion has occurred using pixel values. It comprises three circuits: a motion vector checker 202 for checking whether or not block noise is present, and a block distortion determiner 203 for comprehensively determining whether or not block distortion has occurred based on the outputs of these two checkers. This block distortion detector 109 includes an image memory 1
07 from the variable-length decoder 10
2, motion vectors are input.

The pixel value inspector 201 is provided in the image memory 107
Receives image data from. In the pixel value inspector 201,
Using the peripheral pixel values at the block boundary, it is determined whether or not block distortion occurs at the block boundary, and if block distortion occurs, its intensity is determined. As a method of detecting block distortion using pixel values, for example, as disclosed in Japanese Patent Publication No. 2643636,
Block distortion occurs when the absolute value of the difference between two pixels adjacent to each other across the block boundary is larger than the absolute value of the difference between each two pixels closest to the block boundary in two adjacent blocks. There is a method of determining whether or not to perform block distortion. However, this publication differs from the first embodiment in that the first embodiment detects not only the presence or absence of block distortion but also the intensity thereof.

The operation of the pixel value inspector 201 will be described with reference to FIG. FIG. 3 is a schematic diagram illustrating pixel values of pixels in a certain horizontal direction. In FIG. 3, the horizontal axis represents a pixel position, and the vertical axis represents a pixel value. It is also assumed that a block boundary is between pixel d and pixel e. Now, in FIG. 3A, condition 1: the absolute value of the difference between the pixel values of pixel d and pixel e is greater than a first predetermined value (threshold) TH1 Condition 2: pixel b and pixel c, pixel c and the pixel d, the pixel e and the pixel f, and the pixel absolute value of the pixel f and the pixel absolute value of the pixel g are all the second.
If two conditions smaller than the predetermined value (threshold) TH2 are satisfied, it is determined that block distortion has occurred between the pixel d and the pixel e. The predetermined value TH1 is the lower limit of the absolute value of the difference between two pixels sandwiching the block boundary, and the predetermined value TH1
Since 2 is the upper limit of the absolute value of the difference between two pixels adjacent to each other in the block, it is correctly determined that block distortion always occurs between these predetermined values TH1 and TH2 if the relationship TH1> TH2 holds. Although it is possible, depending on the values of the pixels b, c, d, e, f, and g, even if this relationship does not always hold, it may be possible to correctly determine that block distortion has occurred only under the above conditions 1 and 2. . FIG. 3A shows the conditions 1 and 2 described above.
Is satisfied.

FIG. 3B does not satisfy the conditions 1 and 2, but sets the predetermined values TH1 and TH2 to TH1 and T2, respectively.
First and second predetermined values TH which are values larger than H2
By changing to 1 ′ and TH2 ′, the above conditions 1 and 2 are satisfied. In this case, it is determined that block distortion has occurred between the pixel d ′ and the pixel e ′ in FIG.

In this case, it is determined in FIG. 3B that weak block distortion has occurred, and in FIG. 3A, it is determined that strong block distortion has occurred. This is because, in the case of FIG. 3B, the difference between the pixel values of the pixels in the block is large, so that even if block distortion occurs, it is hardly noticeable.
The absolute value of the difference between the pixel values of the pixels in the block becomes a large value.
Must be changed to larger values TH1 ′ and TH2 ′.

It is desirable that the relationship of TH1 '>TH2' also holds between TH1 'and TH2'. Pixel value inspector 201
Then, this determination result is output to the block distortion determiner 203.

FIG. 4 is a flowchart showing the operation of the pixel value inspector 201 described above. In step S101, image data for performing block distortion determination is received from the image memory 107, and in step S102, a block boundary is detected. . This block boundary can be easily detected by counting eight pixels at a time. Next, in step S103, the above-described condition 1, that is, the pixel d
It is determined whether or not the absolute value of the difference between the value of the pixel e and the value of the pixel e is greater than a predetermined value TH1. If it is larger, in step S104, the above-mentioned condition 2, that is, the absolute differences of the values of the pixels b and c, the pixels c and d, the pixels e and f, and the values of the pixels f and g are all smaller than the predetermined value TH2 It is determined whether or not.
If it is smaller, in step S105, it notifies the block distortion determiner 203 that strong block distortion has occurred. On the other hand, if the determination result is negative in step S103 or step S104, step S1
At 06, it is determined whether or not the absolute value of the difference between the value of the pixel d and the value of the pixel e is greater than a predetermined value TH1 'which is larger than the above-described predetermined value TH1. If it is larger, in step S107, the predetermined value TH that is larger than the above-described predetermined value TH2.
From 2 ′, it is determined whether or not the absolute values of the differences between the pixel values of the pixels b and c, the pixel c and the pixel d, the pixel e and the pixel f, and the pixel f and the pixel g are all small. If smaller, step S108
, The block distortion determination unit 203 is notified that weak block distortion has occurred. On the other hand, if the determination result is negative in step S106 or step S107, in step S109, the block distortion determination unit 203 is notified that no block distortion has occurred.

The motion vector checker 202 receives a motion vector from the variable length decoder 102. In the motion vector tester 202, based on the magnitude of the motion vector,
The presence and absence of block distortion are detected. For example, if the magnitude of the motion vector is larger than the third predetermined value (threshold) TH3, TH4 (though TH3> TH4), a strong block distortion occurs. Is determined, and when the predetermined value TH4 or more, T
If it is equal to or less than H3, it is determined that weak block distortion has occurred. If it is equal to or less than the predetermined value TH4, it is determined that no block distortion has occurred. Here, as a motion vector used for the determination, when detecting block distortion at a certain macroblock boundary, whether the maximum value of one of the motion vectors of two adjacent macroblocks at the macroblock boundary satisfies the above condition is satisfied. The determination may be made according to The motion vector inspector 202 outputs the result of the determination to the block distortion determiner 203.

FIG. 5 shows the motion vector tester 2 described above.
02 is a flowchart showing the operation of Step S2.
At 01, a motion vector is input from the variable length decoder 102. Next, in step S202, it is determined whether the motion vector is larger than a predetermined value TH3. If it is larger, it notifies the block distortion determiner 203 that strong block distortion has occurred. On the other hand, step S201
If the determination result is NO in step S204, it is determined in step S204 whether the motion vector is equal to or more than the predetermined value TH4 and equal to or less than TH3. If this condition is satisfied, in step S205, the block distortion determination unit 203 is notified that weak block distortion has occurred. On the other hand, if the determination result is negative in step S204, in step S206, the block distortion determination unit 203 is notified that no block distortion has occurred.

The block distortion determination unit 203 receives the detection result of the block distortion based on the pixel value from the pixel value inspection unit 201 and the detection result of the block distortion based on the magnitude of the motion vector from the motion vector inspection unit 202. Receive as. The block distortion determiner 203 determines the presence / absence of the final block distortion and the strength thereof based on the detection results of the two block distortions. An example of this determination method is shown in (Table 1). (Table 1) shows, for example, the pixel value inspector 20.
If the determination result of No. 1 is “weak block distortion” and the determination result of the motion vector tester 202 is “strong block distortion”, it indicates that it is determined that “strong block distortion” has occurred. I have. Block distortion determiner 203
Performs the final block distortion determination by executing the table search of (Table 1).

[0050]

[Table 1] In Table 1 above, the determination result of the pixel value inspector 201 is prioritized over the motion vector inspector 202. This is because the motion vector is outside the block distortion determiner 203, that is, at the encoding stage. Therefore, in order to enhance the reliability of the determination, a pixel value that can be determined inside the block distortion determiner 203 is transmitted, because a signal that is not suitable for the determination of the block distortion may be transmitted depending on the encoding method. This is because the judgment result of the inspection device 201 is emphasized. By improving the reliability of the determination in this way, it is possible to perform appropriate correction at the time of image correction when removing block distortion, and it is possible to suppress image quality degradation caused by performing inappropriate correction. .

The result of determination by the block distortion determiner 203 is output to the block distortion remover 108. The block distortion remover 108 receives the image data from the image memory 107 and the block distortion detection result from the block distortion detector 109 as inputs. Block distortion remover 10
In step 8, based on the detection result of the block distortion detector 109, a low-pass filter is applied to the pixels input from the image memory 107 to remove block distortion. An example of the operation will be described with reference to FIG.

FIG. 6A is a schematic diagram showing the same pixels as in FIG. 3A. Now, it is assumed that the block distortion detector 109 determines that strong block distortion has occurred at the block boundary in FIG. In this case, it is assumed that a filter is applied to two pixels at the block boundary. That is, in FIG. 6A, a filter is applied to the pixels c, d, e, and f. Also, the filter strength has a strong effect on pixels d and e and a weak effect on pixels c and f.
And so on. When a low-pass filter is used, as shown in FIG. 7, if the filter strength is high, the cutoff frequency is low and the attenuation is large. This can be realized by increasing the number of taps. The characteristic A in FIG. 7 is a filter having a strong filter strength applied to pixels having strong block noise. For example, a 5-tap filter is used. The characteristic B in FIG. 7 is a filter with a weak filter strength applied to pixels having weak block noise. For example, a three-tap filter is used.

FIG. 8 shows an example of the configuration of a low-pass filter included in the block distortion remover 108. FIG. 8 (a) shows an example of a three-tap filter, FIG. Each is shown. FIG. 8C shows that the number of taps can be switched with one filter by switching a switch.

In FIG. 8, 1081, 1082, 10
Reference numerals 83 and 1084 denote delay units for delaying the respective input signals by a predetermined time, 1085, 1086, 1087,
1088, 1089 are multipliers for multiplying the respective input signals by predetermined filter coefficients α1, α2, α3, α4, α5, 1101 are multipliers 1085, 1086, 108
7, an adder 1102 for adding the outputs of 7
Adders for adding the outputs of 5, 1086, 1087, 1088 and 1089 are switches 1090, 1091 and 1092.

The switches 1090 and 1091 are turned on when the block distortion detector 109 detects that the block distortion is strong, and the circuit of FIG. Is turned off when it is detected that this is the case, and the circuit of FIG. 8C is a 3-tap low-pass filter. Also, the switch 1092
8C is turned on for a pixel other than the vicinity of the block boundary or for a pixel when it is detected that there is no block distortion, so that the low-pass filter is not applied to the image data from the image memory 107. Is bypassed.

FIG. 6A shows a case where a low-pass filter with 5 taps is applied to the pixel d and a low-pass filter with 3 taps is applied to the pixel c. By performing such processing, a pixel value as shown in FIG. 6B is obtained.

FIG. 6C is a schematic diagram showing the same pixels as in FIG. 3B. Now, it is assumed that the block distortion detector 109 determines that weak block distortion has occurred at the block boundary in FIG. In this case, it is assumed that a filter is applied to one pixel at the block boundary. That is, in FIG. 6C, the filters are applied to the pixels d ′ and e ′. FIG. 6C shows a case where a low-pass filter of three taps is applied to the pixel d ′. By performing such processing, a pixel value as shown in FIG. 6D is obtained. The image data processed by the block distortion remover 108 is output as an output image.

As described above, in the block distortion detecting method and the block distortion detecting apparatus according to the first embodiment, first, the difference value between the pixel values at the block boundary and the difference value between the pixel values inside the block are compared with the predetermined value. The presence or absence of block distortion and its strength are detected from the comparison result. Next, based on the magnitude of the motion vector, presence / absence of block distortion and its strength are detected. Then, by combining the detection result of the block distortion based on the pixel value and the detection result of the block distortion based on the magnitude of the motion vector, the presence / absence of the final block distortion and its strength are detected.

In the method and the apparatus for removing block distortion according to the first embodiment, the presence or absence of the block distortion and its intensity are detected, and then a filter corresponding to the intensity is applied to remove the block distortion. Do.

By the above operation, the block distortion detecting method and the block distortion detecting apparatus according to the first embodiment detect the block distortion based on the pixel value and the block distortion based on the magnitude of the motion vector. Since the final presence / absence of block distortion and its strength are detected in combination with the result, it is possible to detect block distortion that could not be detected with conventional pixel values or motion vectors alone. Conversely, it is possible to eliminate the erroneous detection that has been determined to be block distortion based on the detection result of only the pixel value or the motion vector. In addition, by using the block distortion removing method and the block distortion removing device according to the first embodiment, it is possible to perform noise removal according to the intensity of the block distortion, so that blurring of an image is minimized and reliably. Block distortion can be removed without erroneous detection.

In the first embodiment, the case where the MPEG-2 system is used as the encoding system has been described. However, if the encoding system uses motion compensation, the MPEG-2 system is used.
1, MPEG-4, H .; 261, H .; 263, etc., may be used. However, the size of the block,
The size of the motion compensation unit differs depending on the encoding method.

In the first embodiment, the case where the pixel value inspector 201 and the motion vector inspector 202 detect the intensity of block distortion in two stages of weak or strong has been described. May be required in a plurality of stages.

Further, in the first embodiment, the case where the pixel value inspector 201 detects the presence or absence and the intensity of block noise using the pixels b to g is described. May be detected. Alternatively, the detection may be performed using a smaller number of pixels.

In the first embodiment, the case has been described where the motion vector tester 202 determines that block distortion occurs if any one of the motion vectors of two adjacent macroblocks is larger than a predetermined value. This may be determined by another method, for example, if both are larger than a predetermined value, block distortion occurs.

Also, in the first embodiment, the block distortion determining unit 203 has been described as performing the final block distortion determination using (Table 1). However, the final block distortion determination method is as follows. It is not limited to the combination of (Table 1).

Further, in the first embodiment, the case where the filter used in the block distortion remover 108 is a low-pass filter has been described. A filter or a non-linear filter may be used.

Further, in the first embodiment, when the type of the filter is a medium filter, the block boundary
The case where the filter is applied to the pixel and the filter is applied to the six pixels at the block boundary when the type of the filter is a strong filter has been described. There may be.

Further, in the first embodiment, the case where the block distortion at the horizontally adjacent block boundary is detected and removed has been described. However, the same processing can be applied to the vertically adjacent block boundary. .

In the first embodiment, when inter-frame encoding is performed in the pixel value inspector 201, block distortion is detected using pixel values, and the motion vector Although the method and apparatus for detecting block distortion using vectors have been described, the block distortion may be detected using only the pixel value inspector 201. In particular, when intra-frame encoding is performed and there is no motion vector information, the pixel value inspector 2
Block distortion may be detected using only 01.

(Embodiment 2) Embodiment 2 corresponds to the twelfth and twenty-fourth aspects of the present invention. The second embodiment is different from the first embodiment in that the block distortion remover 1
08 is different. Therefore, only the operation of the block distortion remover 108 will be described here.

FIG. 9 shows the configuration of the block distortion remover 108 according to the second embodiment. The block distortion remover 108 includes a filter 501 and a weighted average calculator 502.

The block distortion remover 108 receives the image data from the image memory 107 and the block distortion detector 109.
, The block distortion detection result is input.
The image data input from the image memory 107 is input to the filter 501 and the weighted average calculator 502. The filter 501 filters all the pixels near the block boundary. This is, for example, a process of applying a 5-tap low-pass filter to a pixel adjacent to a block boundary and applying a 3-tap low-pass filter to a pixel adjacent thereto. The output of the filter 501 is output to the weighted average calculator 502.

The weighted average calculator 502 receives the image data from the image memory 107, the image data obtained by filtering the pixels at the block boundaries from the filter 501, the detection result of the block distortion from the block distortion detector 109, Entered respectively. Weighted average calculator 502
Is calculated based on the block distortion detection result.
7 and the image data input from the filter 501 are weighted and averaged and output.
This will be described with reference to FIG.

FIG. 10 is a schematic diagram showing pixels near the block boundary and their pixel values. In FIG. 10, the horizontal axis indicates a pixel position, and the vertical axis indicates a pixel value. FIG. 10 (a)
Is the image data input from the image memory 107, and FIG. 10B is the image data input from the filter 501. That is, the pixels c to c in FIG.
f is a pixel generated by applying a low-pass filter to the pixel of FIG.

Now, the block distortion detector 109 sets the intensity of the block distortion to one of “none”, “weak”, and “strong”.
It is assumed that one distortion is determined. When the block distortion at the block boundary is detected as “absent” by the block distortion detector 109, the weighted average calculator 502 outputs the image data of FIG. Output the data as is. When the block distortion at the block boundary is detected as “weak”, the weighted average calculator 502 calculates the image data of FIG. 10A and the image data of FIG. Are averaged and output. That is, the image data input from the image memory 107 and the image data input from the filter 501 are weighted and averaged and output. In this case, the image data is as shown in FIG. When the block distortion at the block boundary is detected as “strong”, the weighted average calculator 502 outputs the image data shown in FIG.
That is, the image data input from the filter 501 is output as it is.

As described above, the block distortion removing method and the block distortion removing apparatus according to the second embodiment
The presence or absence of the detected block distortion and its strength are input,
A filter is applied to all pixels near the block boundary of the input image, and the input image and the filtered image are weighted and averaged according to the strength of block distortion and output.

With such an operation, by using the block distortion removing method or the block distortion removing apparatus according to the second embodiment, it is not necessary to change the combination of filters according to the strength of the detected block distortion. The removal according to the strength of the block distortion can be performed only by the kinds of filters. This makes it possible to reduce the hardware scale and the like. In addition, although there is only one type of filter, the weight between the input image and the filter image is changed in accordance with the strength of the block distortion. Reliable and without false detection while minimizing
Block distortion can be removed.

Although the second embodiment has been described with reference to the case where the strength of the block distortion is detected in two stages of weak or strong, the number of stages may be three or more. Also, in this case, the stronger the block noise,
The weight for the image data input from the filter 501 may be increased.

In the second embodiment, the filter 5
In FIG. 01, a case has been described where a filter is applied to four pixels at the block boundary. However, the range of pixels to be filtered may be different from that in the second embodiment.

In the second embodiment, the case where the block distortion at the horizontally adjacent block boundary is detected and removed has been described. However, the same processing can be applied to the vertically adjacent block boundary. .

(Embodiment 3) Embodiment 3 corresponds to the inventions of claims 5 to 11 and 17 to 23. FIG. 11 is a block diagram showing an MPEG-2 decoder having a block distortion detecting device and a block distortion removing device that execute the block distortion detecting method and the block distortion removing method according to the third embodiment. In the figure, a variable length decoder 102, an inverse quantizer 103,
Inverse DCT unit 104, adder 105, motion compensator 106,
The image memory 107 is the same as in FIG.

The block distortion detecting device and the block distortion removing device according to the third embodiment further include a block distortion removing unit 108, a block distortion detecting unit 709, and a resolution judging unit 710. The resolution determiner 710 determines which range the resolution belongs to by referring to resolution data included in the decoding result of the MPEG-2 code string.

Variable length decoder 102, inverse quantizer 10
3. Inverse DCT unit 104, adder 105, image memory 10
The operation of 7 is the same as that of the first embodiment, and the description is omitted. However, in the third embodiment, the variable length decoder 1
02 is different from the first embodiment in that it has a function of outputting information on the resolution obtained from the input code string, that is, the number of pixels, to the resolution determiner 710.

The resolution determiner 710 receives the video resolution from the variable length decoder 102, that is, the number of horizontal pixels and the number of vertical pixels of the screen. The resolution determiner 710 determines whether the resolution is equal to or higher than a predetermined resolution. Then, the determination result is output to the block distortion detector 709.

Next, the operation of the block distortion detector 709 will be described. FIG. 12 is a block diagram showing the internal configuration of the block distortion detector 709. As shown in FIG. 12, the block distortion detector 709 includes a pixel value inspector 801, a motion vector inspector 802, and a block distortion determiner 203. The block distortion detector 709 receives the decoded image data from the image memory 107, the motion vector from the variable length decoder 102, and the resolution determination result from the resolution determiner 710.

The pixel value inspector 801 is provided in the image memory 107
, And the resolution determination result from the resolution determiner 710, respectively. Pixel value inspection device 8
01 is the pixel value tester 20 according to the first embodiment when the resolution determined by the resolution determiner 710 is low.
The same operation as in 1 is performed. That is, in FIG. 3A, the difference absolute value of the pixel value between the pixel d and the pixel e is the predetermined value T.
Larger than H1, pixels b and c, pixels c and d,
If the absolute value of the difference between the pixel values of the pixel e and the pixel f and the pixel value of the pixel f and the pixel g is all smaller than the predetermined value TH2, the pixel d and the pixel e
It is determined that block distortion has occurred during.

When the resolution is high, the block distortion is detected with a smaller processing amount than the operation of the pixel value inspector 201 in the first embodiment. Here, as a method of reducing the processing amount, for example, there are a method of reducing the number of pixels used for detecting block distortion, a method of reducing the number of steps of the detection intensity of block distortion, and the like. To reduce the number of pixels used for detecting block distortion, for example, the first embodiment
In FIG. 3, the case where the detection is performed using the pixels b to g is described. However, the detection may be performed using the pixels c to f. When the number of steps of the detection strength of the block distortion is reduced, for example, in the first embodiment, the pixel value is compared with the predetermined values TH1 and TH2 and the predetermined values TH1 ′ and TH2 ′ which are larger than the predetermined values TH1 and TH2 ′. Although the classification is made into three stages of "absence", "weak", and "strong", it may be classified into two stages of block distortion "presence" and "absence". The pixel value inspector 201 outputs this determination result to the block distortion determiner 203.

The motion vector checker 802 receives a motion vector from the variable length decoder 102 and a resolution determination result from the resolution determiner 710, respectively. When the resolution determined by the resolution determiner 710 is low, the motion vector inspector 802 performs the same operation as the motion vector inspector 202 according to the first embodiment. That is, the motion vector tester 802 detects the presence / absence of block distortion and its strength based on the magnitude of the motion vector. For example, when the magnitude of the motion vector is larger than the predetermined value TH3 with respect to the predetermined values TH3 and TH4, it is determined that strong block distortion has occurred. Determines that weak block distortion has occurred, and determines that no block distortion has occurred if it is equal to or less than the predetermined value TH4.

When the resolution is high, the motion vector is inspected with a smaller processing amount than the operation of the motion vector inspector 202 in the first embodiment. Here, as a method of reducing the processing amount, there is a method of reducing the number of stages of detecting the block distortion of the motion vector, or not detecting the block distortion by the motion vector.

The block distortion judgment unit 203 receives the detection result of the block distortion based on the pixel value from the pixel value inspection unit 801 and the detection result of the block distortion based on the magnitude of the motion vector from the motion vector inspection unit 802. Receive as The block distortion determiner 203 determines the presence / absence of the final block distortion and the strength thereof based on the detection results of the two block distortions. This operation is the same as in the first embodiment, and a description thereof will not be repeated. The determination result of the block distortion determiner 203 is output to the block distortion remover 108.

The block distortion remover 108 converts the image data from the image memory 107 into a block distortion detector 709.
Receives the detection result of the block distortion as an input. In the block distortion remover 108, the block distortion detector 70
Based on the detection result of No. 9, block distortion is removed. The operation is the same as in the first embodiment or the second embodiment, and the description is omitted.

As described above, in the block distortion detecting method and the block distortion detecting apparatus according to the third embodiment, first, the difference between the pixel value at the block boundary and the difference between the pixel values inside the block are compared with the predetermined value. The presence or absence of block distortion and its strength are detected from the comparison result. Next, based on the magnitude of the motion vector, presence / absence of block distortion and its strength are detected. At this time, the processing method is changed according to the resolution of the input video, and the higher the resolution, the smaller the amount of processing to detect the block distortion. Then, by combining the detection result of the block distortion based on the pixel value and the detection result of the block distortion based on the magnitude of the motion vector, the presence / absence of the final block distortion and its strength are detected.

By using the block distortion detecting method and the block distortion detecting device according to the third embodiment, the detection result of the block distortion based on the pixel value and the block distortion based on the magnitude of the motion vector are obtained. Since the presence and intensity of the final block distortion are detected together with the distortion detection result, it is possible to detect the occurrence of block distortion that could not be detected with conventional pixel values or motion vectors alone. it can. Conversely, it is possible to eliminate the erroneously detected block distortion using only the pixel value or the motion vector.

In addition, by using the block distortion removing method and the block distortion removing device according to the third embodiment, noise removal is performed in accordance with the strength of the block distortion. Block distortion can be removed without erroneous detection.
Also, the higher the resolution of the input video, the smaller the amount of processing to detect block distortion. That is, when the resolution is low, the processing amount of the decoding processing is small and the block distortion removal processing is large, and when the resolution is high, the decoding processing amount is large and the block distortion removal processing is small. Become
It is possible to suppress the total processing amount of the decoding processing and the block noise removal processing.

Although the third embodiment has been described with reference to the case where the MPEG-2 system is used as the encoding system, if the encoding system uses motion compensation, the MPEG-2 system is used.
1, MPEG-4, H .; 261, H .; In addition to H.263, any coding method may be used. However, the size of the block and the size of the motion compensation unit are different depending on the encoding method.

In the third embodiment, the case where the processing amount is reduced by both the pixel value inspector 801 and the motion vector inspector 802 when the resolution of the input image is high has been described. Only one of the processing amounts may be reduced.

Further, according to the third embodiment, the pixel value inspector 80 is provided in two stages, that is, when the resolution of the input image is high or low.
Although the description has been given of the case of switching the processing amount of 1 and the motion vector inspector 802, the number of stages may be “2” or more.

Further, in the third embodiment, when inter-frame encoding is performed in pixel value inspector 801, block distortion is detected using pixel values, and motion vector inspector 802 detects Although the method and apparatus for detecting block distortion using vectors have been described, the block distortion may be detected using only the pixel value inspector 801. In particular, when intra-frame encoding is performed and there is no motion vector information, the pixel value inspector 8
Block distortion may be detected using only 01.

Further, in the first to third embodiments,
The block distortion at the boundary between the blocks is detected and removed. However, the block distortion at the boundary between the blocks and the motion compensation unit, that is, the boundary between the blocks and the motion compensation unit which is also the boundary between the macroblocks is detected. Detection and removal may be performed, and the same effects as those of the embodiments can be obtained.

[0100]

As described above, according to the block distortion elimination method according to the first aspect of the present invention, an image signal obtained by dividing an image signal into blocks composed of a plurality of pixels and then decoding the coded code sequence is obtained. For the decoded image signal to be obtained, a first difference value between pixels spanning the inter-block boundary and a second difference value between pixels belonging to the block near the inter-block boundary are obtained. Since the pixel value of the pixel near the boundary between the blocks is corrected according to the difference value of 1 and the second difference value, block distortion can be reduced and image quality degradation can be suppressed. effective.

Further, according to the block distortion detecting method according to the second aspect of the present invention, a decoded image signal obtained by dividing an image signal into blocks composed of a plurality of pixels and then decoding a coded code sequence is obtained. And a second difference value between pixels belonging to the block near the inter-block boundary and a second difference value between pixels belonging to the block near the inter-block boundary are calculated. When the absolute value is larger than a first threshold value and the absolute value of the second difference value is smaller than a second threshold value, it is determined that block distortion occurs between the block boundaries, and As the first and second thresholds are smaller, it is determined that stronger block distortion occurs between the block boundaries, so that not only the presence or absence of block distortion but also its intensity can be detected. When performing block distortion correction have an effect of it becomes possible to perform more appropriate correction.

Further, according to the block distortion detecting method according to the third aspect of the present invention, after the image signal is divided into blocks each including a plurality of pixels, at least one block is divided.
For a decoded image signal obtained by decoding a code sequence coded using motion compensation in a unit including two blocks, the inter-block boundary and the boundary of the motion compensation unit, the inter-block / motion compensation First between pixels across unit boundaries
And a second difference value between pixels belonging to the block near the inter-block / motion compensation unit boundary, and the absolute value of the first difference value is calculated from a first threshold value. And the absolute value of the second difference value is smaller than the second threshold value, and the motion amount in the motion compensation unit over the inter-block / motion compensation unit boundary is larger than the third threshold value. When it is larger, it is determined that block distortion occurs between the boundaries, and when the first and second thresholds are smaller, the motion in the motion compensation unit extending between the inter-block / motion compensation unit boundaries is determined. When the amount is large, it is determined that strong block distortion occurs between the boundaries, so that the detection result of the block distortion based on the pixel value and the detection result of the block distortion based on the magnitude of the motion vector Together It can detect the presence or absence of the final block distortion and its strength, just only and motion vector pixel value can be detected block distortion can not be detected. Conversely, it is possible to eliminate the erroneous detection that has been determined to be block distortion based on the detection result of only the pixel value or the motion vector. In addition, when removing block distortion using this detection result, by performing noise removal according to the intensity of block distortion, it is possible to reliably and erroneously detect the image while minimizing blurring of the image. This has the effect that the block distortion can be removed.

According to the block distortion detecting method according to the fourth aspect of the present invention, in the block distortion detecting method according to the third aspect, the motion amount is calculated by calculating Since the maximum value of is used, the detection result of the block distortion based on the pixel value,
By combining the detection result of the block distortion based on the magnitude of the motion vector, the presence / absence of the final block distortion and its strength can be detected, and the block distortion that cannot be detected only by the pixel value or the motion vector alone is detected. be able to.
Conversely, it is possible to eliminate the erroneous detection that has been determined to be block distortion based on the detection result of only the pixel value or the motion vector. In addition, when removing block distortion using this detection result, by performing noise removal according to the intensity of block distortion, it is possible to reliably and erroneously detect the image while minimizing blurring of the image. This has the effect of removing block distortion.

According to the block distortion detecting method according to the fifth aspect of the present invention, a decoded image signal obtained by dividing an image signal into blocks composed of a plurality of pixels and then decoding an encoded code sequence is obtained. And a second difference value between pixels belonging to the block near the inter-block boundary and a second difference value between pixels belonging to the block in the vicinity of the inter-block boundary. When detecting the block distortion between the block boundaries using the value, the larger the resolution of the decoded image signal, the detection of the block distortion by a detection method that reduces the processing amount, so as to, When performing block distortion detection using only pixel values, the detection processing amount can be changed according to the resolution of the target image, and the processing amount does not increase as the image size increases. There is an effect that it is possible to detect the block distortion.

According to the block distortion detecting method according to the sixth aspect of the present invention, after dividing an image signal into blocks each including a plurality of pixels, the block is divided into at least one block.
For a decoded image signal obtained by decoding a code sequence coded using motion compensation in a unit including two blocks, the inter-block boundary and the boundary of the motion compensation unit, the inter-block / motion compensation First between pixels across unit boundaries
And a second difference value between pixels belonging to the block near the inter-block / motion-compensation-unit boundary, and calculating the first and second difference values and the inter-block / motion-compensation-unit When detecting block distortion at the boundary between blocks and between motion compensation units using the amount of motion in a motion compensation unit spanning a boundary, a detection method in which the processing amount decreases as the resolution of the decoded image signal increases. The detection of the block distortion is performed according to the following. Thus, the detection result of the block distortion based on the pixel value and the detection result of the block distortion based on the magnitude of the motion vector are combined to obtain the final block distortion. The presence / absence and its intensity can be detected, and block distortion that cannot be detected by the determination of only the pixel value or the motion vector can be detected. Conversely, in the determination of only the pixel value or only the motion vector, it is possible to eliminate an erroneously detected block distortion. In addition, since noise is removed in accordance with the strength of the block distortion, the block distortion can be removed reliably and without erroneous detection while minimizing blurring of the image. Furthermore, the higher the resolution of the input video, the smaller the amount of processing required to detect block distortion. If the resolution is low, the amount of processing for decoding processing is small, the amount of processing for removing block distortion is large, and the resolution is high. In such a case, the processing amount of the decoding process is large and the block distortion removal process is small, so that there is an effect that the total processing amount of the decoding process and the block noise removal process can be suppressed.

According to the block distortion detecting method of the present invention, in the block distortion detecting method of the fifth or sixth aspect, the decrease in the processing amount corresponds to the detection of the block distortion. Since the detection is performed by reducing the number of pixels used, when detecting block distortion, the number of pixels used for detection of block distortion is changed according to the resolution of the target image to change the detection processing amount. This makes it possible to detect block distortion without increasing the processing amount with an increase in the image size.

According to the block distortion detecting method according to the invention of claim 8 of the present application, in the block distortion detecting method according to claim 5 or 6, the decrease in the processing amount detects the block distortion. This is performed by reducing the number of intensity steps, so that when performing block distortion detection, the intensity level for detecting block distortion is changed according to the resolution of the target image to reduce the amount of detection processing. There is an effect that the block distortion can be detected without increasing the processing amount as the image size increases.

According to the block distortion removing method according to the ninth aspect of the present invention, in the block distortion detecting method according to the sixth aspect, the decrease in the processing amount is caused by the motion amount when the resolution is high. Is performed by not performing the detection of the block distortion by using the method. Therefore, when performing the detection of the block distortion, the detection processing amount can be changed by changing according to the resolution of the target image, and the image size can be changed. There is an effect that it is possible to detect block distortion without increasing the processing amount with the increase in.

According to the block distortion removing method according to the tenth aspect of the present invention, the block distortion is detected by the block distortion detecting method according to any one of the second, third, fifth and sixth aspects. A method for removing the block distortion, wherein the pixel value of a pixel near the block boundary is corrected in accordance with the result of the block distortion determination. Accordingly, there is an effect that more appropriate block distortion can be removed.

Further, according to the block distortion removing method of the present invention, in the block distortion removing method of the tenth aspect, the correction of the pixel value is performed according to the intensity of the block distortion. Since the filtering is performed using different filters, there is an effect that more appropriate block distortion can be removed with improved detection accuracy of the block distortion as compared with the related art.

According to the block distortion removing method according to the twelfth aspect of the present invention, in the block distortion removing method according to the tenth aspect, the pixel value is corrected by applying a predetermined filter to pixels near the boundary. After applying to the pixels of the decoded image, depending on the strength of the block distortion,
By using a weighted average pixel value of the filtered pixels, it is not necessary to change the combination of filters according to the strength of the detected block distortion. Removal according to the strength of the distortion can be performed. This allows
Hardware scale and the like can be reduced. Also,
Although the type of filter is one, since the weight between the input image and the filter image is changed according to the intensity of block distortion, noise removal can be performed according to the intensity of block distortion, and image blurring can be minimized. There is an effect that the block distortion can be removed reliably and without erroneous detection while keeping the limit.

Further, according to the block distortion detecting apparatus of the present invention, the image signal is divided into blocks each including a plurality of pixels, and then the code is obtained by using motion compensation in a unit including at least one of the blocks. An image decoder that receives the converted code sequence as an input, decodes the code sequence to generate a decoded image signal, and further extracts a motion vector used for motion compensation during the decoding, and the decoded image signal As inputs, a first difference value between pixels spanning the inter-block boundary and a second difference value between pixels belonging to the block near the inter-block boundary are obtained, and the absolute value of the first difference value is obtained. Is larger than the first threshold value and when the absolute value of the second difference value is smaller than the second threshold value, it is determined that block distortion occurs at the inter-block boundary,
Also, a pixel value inspector that determines that strong block distortion occurs as the first and second threshold values are smaller is provided, so that not only the presence or absence of block distortion but also its intensity can be detected. When performing block distortion correction using the detection result, there is an effect that more appropriate correction can be performed.

Further, according to the block distortion detecting apparatus of the present invention, the image signal is divided into blocks each including a plurality of pixels, and then a code is generated by using motion compensation in a unit including at least one of the blocks. An image decoder that receives the converted code sequence as an input, decodes the code sequence to generate a decoded image signal, and further extracts a motion vector used for motion compensation during the decoding, and the decoded image signal A first difference value between pixels, which is an input, is the inter-block boundary, and is a boundary of the motion compensation unit, between pixels intersecting the inter-block / motion compensation unit boundary, and the vicinity of the inter-block / motion compensation unit boundary. And the second difference value between the pixels belonging to the block is obtained, the absolute value of the first difference value is larger than a first threshold value, and the absolute value of the second difference value is calculated as a second value. Threshold If remote small aforementioned and inter-block-motion compensation unit between judges pixel value inspector and between boundary block distortion occurs, and inputs the motion vector,
A motion vector tester that determines that block distortion occurs when a motion amount in a motion compensation unit that crosses the inter-block / motion compensation unit boundary is greater than a third threshold value; From the determination result of the block distortion with the motion vector tester, so as to include a block distortion determination unit that determines the presence or absence of the final block distortion, the detection result of the block distortion based on the pixel value, By combining the detection result of the block distortion based on the magnitude of the motion vector, the presence / absence of the final block distortion and its strength can be detected, and the block distortion that cannot be detected only by the pixel value or the motion vector alone is detected. be able to. Conversely, it is possible to eliminate the erroneous detection that has been determined to be block distortion based on the detection result of only the pixel value or the motion vector. In addition, when removing block distortion using this detection result, it is possible to perform noise removal according to the intensity of block distortion, so that blurring of the image is minimized without erroneous detection. There is an effect that the block distortion can be removed.

Further, according to the block distortion detecting device of the present invention, in the block distortion detecting device of the present invention, the pixel value inspector is provided with the first value.
And the second predetermined value is smaller, it is determined that stronger block distortion is generated, and the motion vector tester determines that stronger block distortion is generated as the motion amount is larger. By combining the block distortion detection result based on the block distortion detection result based on the magnitude of the motion vector, the presence or absence of the final block distortion and its strength can be detected. Block distortion that could not be detected can be detected. Conversely, it is possible to eliminate the erroneous detection that has been determined to be block distortion based on the detection result of only the pixel value or the motion vector. In addition, when removing block distortion using this detection result, it is possible to perform noise removal according to the intensity of block distortion, so that blurring of the image is minimized without erroneous detection. There is an effect that the block distortion can be removed.

Further, according to the block distortion detecting apparatus of the present invention, in the block distortion detecting apparatus according to the present invention, the amount of motion is defined by each motion amount of the adjacent motion compensation units. Is used, so that the detection result of the block distortion based on the pixel value and the detection result of the block distortion based on the magnitude of the motion vector are combined to determine whether or not there is a final block distortion. Intensity can be detected, and block distortion that cannot be detected only with pixel values or motion vectors can be detected. Conversely, it is possible to eliminate the erroneous detection that has been determined to be block distortion based on the detection result of only the pixel value or the motion vector. In addition, when removing block distortion using this detection result, it is possible to perform noise removal according to the intensity of block distortion, so that blurring of the image is minimized without erroneous detection. There is an effect that the block distortion can be removed.

Further, according to the block distortion detecting apparatus of the present invention, the image signal is divided into blocks each composed of a plurality of pixels, and then the code is obtained by using motion compensation in a unit including at least one of the blocks. Image decoding which receives a decoded code sequence as input, decodes the code sequence to generate a decoded image signal, and further extracts a motion vector used for motion compensation during the decoding and a resolution of the decoded image signal. And a resolution determiner for determining which range the resolution of the decoded image signal belongs to, and a first difference value between pixels which takes the decoded image signal as input and straddles the inter-block boundary. And a second difference value between pixels belonging to the block near the boundary between the blocks, and the absolute value of the first difference value is larger than a first threshold value, and the second difference value of When the logarithmic value is smaller than a second threshold value, a pixel value inspector that determines that block distortion occurs at the inter-block boundary, and a motion compensation unit that receives the motion vector as an input and spans the inter-block boundary. A motion vector inspector that determines that strong block distortion occurs at the inter-block boundary when the amount of motion of the pixel is greater than a third threshold value; and a block distortion of the pixel value inspector and the motion vector inspector. And a block distortion determiner for determining whether or not a final block distortion has occurred from the determination result.The greater the resolution of the decoded image signal determined by the resolution determiner, the larger the pixel value inspector And the amount of processing in at least one of the motion vector testers is reduced, so that block distortion detection is performed using the pixel value and the amount of motion compensation. When performing, the detection processing amount can be changed according to the resolution of the target image, and the effect that the block distortion can be detected without increasing the processing amount as the image size increases. is there.

Further, according to the block distortion detecting apparatus according to the invention of claim 18 of the present application, after dividing an image signal into blocks each including a plurality of pixels, a code is obtained by using motion compensation in a unit including at least one of the blocks. Image decoding for receiving a decoded code sequence as input, decoding the code sequence to generate a decoded image signal, and further extracting a motion vector used for motion compensation during the decoding and a resolution of the decoded image signal. Device, a resolution determiner for determining whether the resolution of the decoded image signal belongs to a predetermined range, and the decoded image signal as input, the boundary between the blocks, and between the motion compensation unit A first difference value between pixels that is a boundary, which is a boundary between blocks and between motion compensation units, and a second difference value between pixels belonging to the block near the boundary between blocks and between motion compensation units. A difference value, and when the absolute value of the first difference value is larger than a first threshold value and the absolute value of the second difference value is smaller than a second threshold value, A pixel value tester that determines that block distortion occurs between boundaries between inter-motion / motion compensation units, and a motion amount in a motion compensation unit that spans the inter-block / inter-motion compensation unit boundary when the motion vector is input. When the threshold value is larger than the threshold value, a motion vector tester that determines that block distortion is generated, and the final block distortion is generated based on the block distortion determination result of the pixel value tester and the motion vector tester. And a block distortion determiner for determining the presence and absence of the pixel value tester and the motion vector test, as the resolution of the decoded image signal determined by the resolution determiner increases. The amount of processing in at least one of the two is reduced, so that the detection result of the block distortion based on the pixel value and the detection result of the block distortion based on the magnitude of the motion vector are combined to obtain the final block distortion. Since the presence / absence and its strength are detected, it is possible to detect block distortion that could not be detected by the conventional determination using only pixel values or only motion vectors. Conversely, in the determination of only the pixel value or the motion vector, there is an effect that an erroneously detected block distortion can be eliminated.

According to the block distortion detecting apparatus of the present invention, the decrease in the processing amount is caused by the pixel used for detecting the block distortion. The number of pixels used for detecting block distortion is changed according to the resolution of the target image to change the amount of detection processing when performing block distortion detection. Thus, there is an effect that the block distortion can be detected without increasing the processing amount with the increase in the image size.

According to the block distortion detecting device of the present invention, the decrease in the processing amount is caused by the intensity of the block distortion detected. Since the number of stages is reduced, the amount of detection processing is changed by changing the intensity of the block distortion detection according to the resolution of the target image when detecting the block distortion. Thus, there is an effect that the block distortion can be detected without increasing the processing amount with the increase in the image size.

Further, according to the block distortion detecting device of the present invention, in the block distortion detecting device according to claim 17 or 18, the decrease in the processing amount is as follows when the resolution is high. Since the detection is performed by not performing the detection of the block distortion based on the motion amount, it is possible to change the detection processing amount by changing the detection according to the resolution of the target image when performing the detection of the block distortion. There is an effect that the block distortion can be detected without increasing the processing amount with the increase in the image size.

Further, according to the block distortion elimination apparatus according to the invention of claim 22 of the present application, claim 13, claim 14,
19. A device for removing block distortion detected by the block distortion detection device according to claim 17, wherein the decoded video signal and the block distortion determination result are input, and A block distortion remover that corrects the pixel value of a pixel near the boundary of the decoded video signal in accordance with the determination result of the block distortion is provided, so that the detection accuracy of the block distortion is improved compared to the related art. This has the effect of enabling more appropriate block distortion removal.

Further, according to the block distortion removing device of the present invention, in the block distortion removing device according to the present invention, the correction of the pixel value is performed according to the intensity of the block distortion. Since the filtering is performed using different filters, there is an effect that it is possible to more appropriately remove the block distortion with improved detection accuracy of the block distortion as compared with the related art.

Further, according to the block distortion removing apparatus of the present invention, in the block distortion removing apparatus of the present invention, the correction of the pixel value is performed by applying a predetermined filter to pixels near the boundary. After applying to the pixels of the decoded image, depending on the strength of the block distortion,
By using a weighted average pixel value of the filtered pixels, it is not necessary to change the combination of filters according to the strength of the detected block distortion. Removal according to the strength of the distortion can be performed. This allows
Hardware scale and the like can be reduced. Also,
Although the type of filter is one, since the weight between the input image and the filter image is changed according to the intensity of block distortion, noise removal can be performed according to the intensity of block distortion, and image blurring can be minimized. There is an effect that the block distortion can be removed reliably and without erroneous detection while keeping the limit.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining Embodiment 1 of the present invention;

FIG. 2 is a block diagram for explaining a block distortion detector according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram for explaining block distortion.

FIG. 4 is a flowchart illustrating a detection operation of the pixel inspection device according to the first embodiment of the present invention;

FIG. 5 is a flowchart illustrating a detection operation of the motion vector tester according to the first embodiment of the present invention.

FIG. 6 is a schematic diagram for explaining an operation for removing block distortion according to the first embodiment of the present invention.

FIG. 7 is a filter characteristic diagram showing characteristics of a low-pass filter.

FIG. 8 is a diagram showing a configuration example of a 3-tap and 5-tap low-pass filter constituting the block distortion remover according to the first embodiment of the present invention.

FIG. 9 is a block diagram illustrating a configuration example of a block distortion remover according to a second embodiment of the present invention.

FIG. 10 is a schematic diagram for explaining an operation for removing block distortion according to the second embodiment of the present invention.

FIG. 11 is a block diagram for explaining Embodiment 3 of the present invention;

FIG. 12 is a block diagram illustrating a configuration example of a block distortion detector according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 102 variable length decoder 103 inverse quantizer 104 inverse DCT unit 105 adder 106 motion compensator 107 image memory 108 block distortion remover 109 block distortion detector 201 pixel value inspector 202 motion vector inspector 203 block distortion determiner Reference Signs List 501 filter unit 502 weighted average calculator 709 block distortion determiner 710 resolution determiner 801 pixel value inspector 802 motion vector inspector 1081 delay unit 1082 delay unit 1083 delay unit 1084 delay unit 1085 multiplier 1086 multiplier 1087 multiplier 1088 multiplier Unit 1089 Multiplier 1090 Switch 1091 Switch 1092 Switch 1101 Adder 1102 Adder

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C059 KK03 KK11 MA00 MA23 MC11 MC38 ME01 PP04 PP25 TA69 TB08 TC02 TC33 TC42 TD05 TD12 UA02 UA05 UA12 UA33

Claims (24)

[Claims] 1. A first difference between pixels over a boundary between blocks with respect to a decoded image signal obtained by decoding an encoded signal sequence after dividing an image signal into blocks each including a plurality of pixels. A value and a second difference value between pixels belonging to the block near the boundary between the blocks are obtained. According to the value of the first difference value and the second difference value,
Correcting a pixel value of a pixel near a boundary between the blocks. 2. The method according to claim 1, wherein a first difference between pixels across the inter-block boundary is compared with a decoded image signal obtained by decoding an encoded signal sequence after dividing the image signal into blocks including a plurality of pixels. And a second difference value between pixels belonging to the block near the inter-block boundary, wherein the absolute value of the first difference value is greater than a first threshold value, and When the absolute value of the difference value is smaller than a second threshold value, it is determined that block distortion occurs between the block boundaries, and the smaller the first and second threshold values are, the more the block boundary is generated. A block distortion detection method characterized in that it is determined that strong block distortion occurs. 3. A decoded image signal obtained by dividing an image signal into blocks each including a plurality of pixels and then decoding a code string encoded using motion compensation in a unit including at least one of the blocks. , The boundary between the blocks, and the boundary between the motion compensation units.
Calculating a first difference value between pixels spanning a boundary between motion compensation units and a second difference value between pixels belonging to the block near the boundary between the blocks and between motion compensation units; The absolute value of the value is larger than the first threshold value, the absolute value of the second difference value is smaller than the second threshold value, and the motion compensation unit spans the inter-block / motion compensation unit boundary. If the amount of motion is larger than a third threshold value, it is determined that block distortion occurs between the boundaries. If the first and second threshold values are small, the inter-block / motion compensation is performed. When the amount of motion in a motion compensation unit spanning an inter-unit boundary is large, it is determined that strong block distortion occurs between the boundaries. 4. The block distortion detecting method according to claim 3, wherein the motion amount uses a maximum value among the motion amounts of the motion compensation units adjacent to each other. 5. A first difference between pixels across a boundary between blocks with respect to a decoded image signal obtained by decoding an encoded signal sequence after dividing an image signal into blocks each including a plurality of pixels. Calculating a value and a second difference value between pixels belonging to the block near the inter-block boundary, and detecting block distortion between the block boundaries using the first and second difference values. Detecting the block distortion by a detection method in which the processing amount decreases as the resolution of the decoded image signal increases. 6. A decoded image signal obtained by dividing an image signal into blocks each including a plurality of pixels and then decoding a code string coded using motion compensation in a unit including at least one of the blocks. , The boundary between the blocks, and the boundary between the motion compensation units.
Calculating a first difference value between pixels over a boundary between motion compensation units and a second difference value between pixels belonging to the block near the boundary between blocks and between motion compensation units; When detecting block distortion between the inter-block and motion-compensation unit boundaries using the difference value and the amount of motion in the motion compensation unit spanning the inter-block / motion compensation unit boundary, the decoded image signal The block distortion is detected by a detection method in which the processing amount decreases as the resolution of the block distortion increases. 7. The block distortion detection method according to claim 5, wherein the processing amount is reduced by reducing the number of pixels used for detecting the block distortion. Detection method. 8. The block distortion detecting method according to claim 5, wherein the processing amount is reduced by reducing the number of steps of the intensity for detecting the block distortion. Distortion detection method. 9. The block distortion detecting method according to claim 6, wherein the processing amount is reduced by not executing the block distortion detection based on the motion amount when the resolution is high. Block distortion detection method. 10. A method for removing block distortion detected by the block distortion detection method according to claim 2, wherein the block distortion determination result is obtained. And correcting a pixel value of a pixel near the block boundary according to the following. 11. The block distortion removing method according to claim 10, wherein the correction of the pixel value is performed using a filter having a characteristic different according to the intensity of the block distortion. 12. The block distortion removing method according to claim 10, wherein the correction of the pixel value is performed after a predetermined filter is applied to a pixel near the boundary, and the pixel value is corrected according to the strength of the block distortion. A method for removing block distortion, which is performed by using a weighted average pixel value of a pixel of a decoded image and a pixel subjected to the filter. 13. An image signal is divided into blocks each including a plurality of pixels, and a code string coded by using motion compensation in a unit including at least one of the blocks is input, and the code string is decoded and decoded. An image decoder that generates an image signal and further extracts a motion vector used for motion compensation during the decoding; a first difference value between pixels that receives the decoded image signal as input and that spans an inter-block boundary; And a second difference value between pixels belonging to the block near the boundary between the blocks, and the absolute value of the first difference value is larger than a first threshold value, and the second difference value When the absolute value of is smaller than a second threshold, it is determined that block distortion occurs at the boundary between the blocks, and when the first and second thresholds are smaller, stronger block distortion occurs. Judge And a pixel value inspector, block distortion detection apparatus characterized by. 14. After dividing an image signal into blocks each including a plurality of pixels, a code string coded using motion compensation in a unit including at least one of the blocks is input, and the code string is decoded and decoded. An image decoder that generates an image signal and further extracts a motion vector used for motion compensation at the time of the decoding; and an input of the decoded image signal, the inter-block boundary, and a boundary of the motion compensation unit. A first difference value between pixels spanning the boundary between blocks / motion compensation units and a second difference value between pixels belonging to the block near the boundary between blocks / motion compensation units are obtained, When the absolute value of the first difference value is larger than a first threshold value and the absolute value of the second difference value is smaller than a second threshold value, the inter-block / motion compensation unit Between boundaries Click and distortion occurs and determining the pixel value inspector, the inputs the motion vector, the motion amount in the motion compensation units spanning between interblock-motion compensation unit boundary is the third
A motion vector tester that determines that block distortion occurs when the threshold value is larger than the threshold value of the following. A block distortion detecting device comprising: a block distortion determining unit that determines the presence or absence of a block distortion. 15. The block distortion detecting device according to claim 14, wherein the pixel value inspector determines that the smaller the first and second thresholds are, the stronger block distortion is generated, and the motion vector inspection is performed. The vessel, the larger the amount of movement,
A block distortion detecting device, which determines that strong block distortion occurs. 16. The block distortion detecting apparatus according to claim 15, wherein the amount of motion uses a maximum value among the amounts of motion of the motion compensation units adjacent to each other. 17. A method in which an image signal is divided into blocks each including a plurality of pixels, and a code string coded using motion compensation in a unit including at least one of the blocks is input, and the code string is decoded and decoded. An image decoder that generates an image signal, and further extracts a motion vector used for motion compensation during the decoding and a resolution of the decoded image signal, and a resolution of the decoded image signal is in a predetermined range. A resolution determiner for determining whether the pixel belongs to a first pixel, and a first difference value between pixels that spans the inter-block boundary, and a second difference between pixels belonging to the block near the inter-block boundary. When the absolute value of the first difference value is larger than a first threshold value and the absolute value of the second difference value is smaller than a second threshold value, Boundary between blocks A pixel value inspector that determines that block distortion occurs; and an input of the motion vector, wherein when the amount of motion in a motion compensation unit spanning the inter-block boundary is larger than a third threshold value, the inter-block boundary A motion vector inspector that determines that strong block distortion occurs; and a block distortion determination that determines whether or not a final block distortion has occurred based on the block distortion determination results of the pixel value inspector and the motion vector inspector. The resolution is determined by the resolution determiner, the larger the resolution of the decoded image signal, the less the amount of processing in at least one of the pixel value inspector and the motion vector inspector, characterized in that, Block distortion detection device. 18. An image signal is divided into blocks each including a plurality of pixels, and a code string coded using motion compensation in a unit including at least one of the blocks is input, and the code string is decoded and decoded. An image decoder that generates an image signal, and further extracts a motion vector used for motion compensation during the decoding and a resolution of the decoded image signal, and a resolution of the decoded image signal is in a predetermined range. A resolution determiner that determines whether or not the pixel belongs to the input of the decoded image signal, the inter-block boundary, and the boundary between the motion compensation units, between pixels spanning the inter-block / motion compensation unit boundary. Calculating a first difference value and a second difference value between pixels belonging to the block near the inter-block / motion-compensation-unit-interval boundary, wherein the absolute value of the first difference value is a first threshold value Yo Larger,
When the absolute value of the second difference value is smaller than a second threshold value, a pixel value inspector that determines that block distortion occurs between boundaries between the blocks and between motion compensation units; As an input, the amount of motion in the motion compensation unit over the boundary between the blocks and between the motion compensation units is the third
A motion vector tester that determines that block distortion occurs when the threshold value is larger than the threshold value of the following. And a block distortion determiner for determining the presence and absence of the at least one of the pixel value tester and the motion vector tester as the resolution of the decoded image signal, determined by the resolution determiner, increases. A block distortion detection device, which reduces the processing amount in. 19. The block distortion detection device according to claim 17, wherein the processing amount is reduced by reducing the number of pixels used for detecting the block distortion. . 20. The block distortion detection device according to claim 17, wherein the processing amount is reduced by reducing the number of steps of the intensity for detecting the block distortion. apparatus. 21. The block distortion detection device according to claim 17, wherein the processing amount is reduced by not detecting block distortion based on the motion amount when the resolution is high. Characteristic block distortion detecting device. 22. Claim 13, Claim 14, Claim 1
19. An apparatus for removing block distortion detected by the block distortion detection apparatus according to claim 18, wherein the block distortion is input by receiving the decoded video signal and the block distortion determination result. A block distortion remover that corrects a pixel value of a pixel near the boundary of the decoded video signal in accordance with the result of the determination. 23. The block distortion removing device according to claim 22, wherein the correction of the pixel value is performed using a filter having different characteristics according to the intensity of the block distortion. 24. The block distortion removing apparatus according to claim 22, wherein the correction of the pixel value is performed after a predetermined filter is applied to a pixel near the boundary, and the pixel value is corrected in accordance with the strength of the block distortion. A block distortion elimination apparatus, wherein the block distortion elimination is performed by using a weighted average pixel value of a pixel of a decoded image and a pixel subjected to the filter.