JPH08237658A - Picture processor - Google Patents

Abstract

PURPOSE: To suppress block distortion while avoiding the degradation of resolution as much as possible. CONSTITUTION: A frame is divided into many blocks, picture data DCT encoded by a block unit are decoded in a decoder 1 and digital picture signals PTs are outputted. Picture elements near a block boundary line within pictures expressed by the digital picture signals PTs are selected by a horizontal direction selection circuit 10 and a vertical direction selection circuit 20. Then by a spatial frequency filter 30 and a selector 50, the digital picture signal PT' for which the high band spatial frequency components of the picture elements near the block boundary line within the pictures expressed by the digital picture signals PTs are eliminated and the other picture elements are left as they are prepared and outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, and in particular, one frame or one field is divided into a large number of blocks, and each block is subjected to orthogonal transform such as DCT or Hadamard transform for intra-frame coding. Also, the present invention relates to an image processing apparatus capable of suppressing block distortion that occurs when interframe (field) coding is performed by motion detection (MC) prediction using motion detection by a block matching method.

[0002]

2. Description of the Related Art Since an image has a very large amount of information as it is, the amount of information is compressed and stored, transmitted, and reproduced.
The original image is obtained by decompressing upon reception. There are two types of methods for encoding an image with high efficiency and compressing the amount of data: inter-frame (field) encoding and intra-frame (field) encoding. The former representative one is interframe (field) predictive coding which encodes the difference between pixel values at the same position between frames (fields).
Typical of the latter is orthogonal transform coding by DCT (discrete cosine transform). This divides one frame (one field) into many blocks, and each block is D
Converted to DCT coefficient by CT (Discrete Cosine Transform),
It is to be encoded. Normally, hybrid coding combining these two types of methods is performed, and a difference between frames (fields) obtained by interframe (field) predictive coding is converted into a DCT coefficient and coded to achieve high compression. Is getting the rate.

[0003]

However, the DCT
In the technique of encoding in block units such as, there is a problem that a block distortion occurs in a decoded image due to processing by dividing a frame (field) into a large number of blocks, the blocks are visible and the image quality is deteriorated. there were. Especially,
In the inter-frame (field) predictive coding, there is a problem that the amount of information increases in a frame having a large motion and block distortion becomes remarkable. The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide an image processing apparatus capable of suppressing block distortion while avoiding deterioration of resolution as much as possible. Another object is to provide an image processing device having a relatively simple configuration.

[0004]

In the image processing apparatus of the present invention, a frame or field is divided into a large number of blocks, and the image processing apparatus is provided with a decoding means for decoding an image encoded in each block. Selection means for selecting pixels in the vicinity of the block boundary line in the subsequent image,
It is characterized in that a high spatial frequency component removing means for removing high spatial spatial frequency components of pixels near the block boundary line selected by the selective means and leaving other pixels as they are, is provided for the decoded image. There is.

In another image processing apparatus of the present invention, a detecting means for detecting a pixel having a large change between frames or fields in the decoded image is provided, and the high spatial frequency component removing means is provided for the decoded image. On the other hand, the pixels in the vicinity of the block boundary line selected by the selection unit, and the high spatial frequency components are removed from the pixels detected by the detection unit that have a large change between frames or fields, and other pixels remain unchanged. The feature is that

In still another image processing apparatus of the present invention, the removal of high spatial frequency components by the high spatial frequency component removing means averages the pixels around the pixel of interest in the decoded image and replaces it with the pixel of interest. It is characterized by doing.

In another image processing apparatus of the present invention, the removal of high spatial frequency components by the high spatial frequency component removal means removes horizontal high spatial frequency components from pixels near the horizontal block boundary line. However, it is characterized in that the vertical high frequency spatial frequency components are removed from the pixels near the vertical block boundary line.

In another image processing apparatus of the present invention, the removal of horizontal high frequency spatial frequency components by the high frequency spatial frequency component removing means averages horizontal pixels around the pixel of interest in the decoded image. , The removal of high frequency spatial frequency components in the vertical direction is performed by averaging the pixels in the vertical direction around the pixel of interest in the decoded image and replacing it with the pixel of interest. .

[0009]

According to the image processing apparatus of the present invention, the pixels near the block boundary line are selected from the decoded image, and the high spatial frequency components of the pixels near the block boundary line are selected from the decoded image. Remove and leave other pixels as they are. This makes it possible to make the block distortion in the vicinity of the block boundary line inconspicuous while avoiding the deterioration of the resolution in the block.

According to another image processing apparatus of the present invention, a pixel having a large change between frames or fields is detected in the image after decoding, and pixels near the block boundary line are detected in the image after decoding. And, the high spatial frequency component is removed for the pixel whose change between frames or fields is large,
The other pixels are left as they are. This allows block distortion at block boundaries to be less noticeable while avoiding intra-block resolution degradation for large motion frames or fields, and over the entire frame or field for static or small frames or fields. Good resolution can be maintained.

According to still another image processing apparatus of the present invention,
The removal of the high spatial frequency component is performed by averaging the pixels around the pixel of interest in the decoded image and replacing them with the pixel of interest. This makes it possible to remove high frequency spatial frequency components with a simple configuration.

According to another image processing apparatus of the present invention, the high frequency spatial frequency components in the horizontal direction are removed from the pixels near the vertical block boundary line, and the pixels in the vertical direction are removed from the pixels near the horizontal block boundary line. This is performed by removing the high spatial frequency component. This makes it possible to make the block distortion inconspicuous while minimizing the deterioration of resolution near the block boundary line.

According to another image processing apparatus of the present invention, in the removal of the high spatial frequency component in the horizontal direction, the pixels in the horizontal direction are averaged around the pixel of interest in the decoded image, and the pixel of interest is replaced. The removal of the high spatial frequency component in the vertical direction is performed by averaging the pixels in the vertical direction around the pixel of interest in the image after decoding and replacing them with the pixel of interest. This makes it possible to remove horizontal high frequency spatial frequency components and vertical high frequency spatial frequency components with a simple configuration.

[0014]

1 is a circuit diagram of an image processing apparatus according to an embodiment of the present invention. Here, the image size is vertical × horizontal = 352
A monochrome image of × 240 is targeted (see (1) of FIG. 3), and the pixel value of each pixel is quantized in 2 ⁸ steps of 0 to 255, and black level = 16 and white level = 235. Reference numeral 1 denotes a decoder that decodes image data that is highly efficient coded by hybrid coding that is a combination of interframe coding by interframe predictive coding and intraframe coding by DCT coding. A digital image signal PT obtained by scanning an image in a non-interlaced system is output, and a digital image signal P is output.
A pixel clock PCK, a line clock LCK, and a frame clock FCK synchronized with the output of T are output. As shown in FIG. 2, the pixel clock PCK is a clock having the same cycle as the sampling frequency of the pixel, and the line clock L
CK is a clock that is at H level for a period slightly longer than the pulse width of PCK from the start timing of one line, and frame clock FCK is a clock that is at H level for 1/2 line from the start timing of the head line of one frame.

The DCT coding method will be described with reference to FIG. As shown in FIG. 3 (1), the DCT coding is performed by dividing one frame into blocks each having a size of length × width = 16 × 16, converting the DCT coefficients in block units, and coding the DCT coefficients. D
In the digital image signal PT in which the CT coded image data is still decoded, the block boundary is visible due to block distortion. As will be described later, in the present embodiment, by selecting pixels near the block boundary and removing (attenuating) the high spatial frequency component, the block distortion at the block boundary is avoided while avoiding the deterioration of the resolution within the block. Make it inconspicuous.

The relation between the pixel coordinates and the block coordinates will be described. The coordinates of each pixel in one frame are P
(X, y) [x = 0 to 351, y = 0 to 239], and the block coordinates are B (i, j) [i = 0 to 21, j = 0 to 1
4] as shown in FIG. 3 (2), each block B
The x, y coordinates of the pixel immediately inside the boundary line of (i, j) are as follows: V ₁ range: x = 16i, y = 16j to 16j + 15 V ₂ range: x = 16i + 15, y = 16j to 16j + 15 range of _{H 1 ·· x = 16i~16i + 15} , y = range _{16j H 2 ·· x = 16i~16i +} 15, a y = 16j + 15.

Returning to FIG. 1, reference numeral 2 is a motion detection circuit for detecting a pixel having a certain amount of motion (a large change of a certain amount or more) between frames. Of these, 3 is a digital signal input from the decoder 1. The 1-frame delay circuit 4 for delaying the image signal PT by 1 frame subtracts the output of the 1-frame delay circuit from the digital image signal to change the pixel value at the same position one frame before for each pixel in the frame. The subtracter 5 for obtaining the value (difference) compares 20 with the absolute value of the difference obtained by the subtractor, and when it exceeds 20, it outputs H indicating that the pixel value has changed significantly,
A comparator circuit 6 outputs L in the following cases, and a 1-line delay circuit 6 delays the output of the comparator circuit 5 by one line and outputs it as the first select signal A.

Reference numeral 10 is a horizontal direction selection circuit for selecting pixels in the image indicated by the digital image signal PT, the horizontal position of which is near the vertical boundary line of the block. Of these, 11 is a counter. Then the line clock LCK
Is cleared during H, then the pixel clock PC
Every time K is input, 0 to 15 are cyclically counted. In the image of FIG. 3, the x coordinate of the pixel is block B.
1 corresponding to the right side of the vertical boundary line on the left side of (i, j)
When 6i (however, i = 0 to 21), the count value of the counter 11 becomes 0, and when x = 16i + 1, the count value = 1, x =
When 16i + 2, count value = 2, ..., x = 16i + 1
When 4, the count value = 14. 16 (i + 1) +15, where the x-coordinate corresponds to the immediate left side of the right vertical boundary of the block
At this time, the count value of the counter 11 becomes 15. Reference numeral 12 is a comparison circuit, which outputs an H level when the count value of the counter 11 matches 0 or 15, and outputs an L level when the count value does not match 0 or 15. 13 is a comparison circuit 1
This is a 1-line delay circuit that delays the output of 2 by 1 line and outputs it as the second select signal B.

Reference numeral 20 is a vertical direction selection circuit for selecting pixels in the image indicated by the digital image signal PT, the vertical position of which is near the horizontal boundary line of the block. Of these, 21 is a counter. Then, the frame clock FC
K is cleared while H, then line clock LC
Every time K is input, 0 to 15 are cyclically counted. In the image of FIG. 3, the y coordinate of the pixel is the block B.
1 corresponding to just below the upper horizontal boundary of (i, j)
When 6j [where j = 0 to 14], the count value of the counter 21 becomes 0, and when y = 16j + 1, the count value = 1, y =
When 16j + 2, count value = 2, ..., y = 16j + 1
When 4, the count value = 14. 16 (j + 1) +1 in which the y coordinate is immediately above the lower horizontal boundary line of the block
When it is 5, the count value of the counter 21 is 15. Reference numeral 22 is a comparison circuit, which outputs an H level when the count value of the counter 21 matches 0 or 15 and the count value is 0 or 15
When it does not match with, the L level is output. Reference numeral 23 delays the output of the comparison circuit 22 by one line to output the third select signal C.
Is a one-line delay circuit that outputs as. The horizontal direction selection circuit 20 and the vertical direction selection circuit 30 select pixels in the vicinity of the block boundary line in the image decoded by the decoder 1.

Assuming that the current pixel position of the digital video signal PT is P (x, y + 1), the output of the 1-line delay circuit 6 of the motion detection circuit 2 is above a certain level for the pixel of P (x, y). Movement (large change above a certain level)
(1; motion is present, 0: no motion is present), and the output of the 1-line delay circuit 13 of the horizontal direction selection circuit 10 is immediately after the vertical boundary line of the block for the pixel whose pixel position is P (x, y). Indicates whether the pixel is on the right side or the left side (1; near the vertical boundary line, 0; other than near the vertical boundary line), and the output of the 1-line delay circuit 23 of the vertical direction selection circuit 20 has a pixel position of P ( (x, y) indicates whether the pixel is a pixel immediately below or above the horizontal boundary line of the block (1; near the horizontal boundary line, 0; other than near the horizontal boundary line).

Reference numeral 30 denotes a spatial frequency filter, which is a signal from which high-frequency spatial frequency components in the horizontal and vertical directions are removed, a signal from which high-frequency spatial frequency components in the horizontal direction are removed, and a vertical direction based on the digital video signal PT. The signal from which the high spatial frequency component of is removed is output. Also, a signal obtained by simply delaying the digital video signal PT by one line is output. In the spatial frequency filter 30, 31 is a delay circuit for 239 pixels, 32 and 33 are delay circuits for 1 pixel each, and 34 is a delay circuit for 239 pixels. Reference numeral 35 is a digital video signal PT and delay circuits 31 to 34.
Adder 36 adds 1 to the output of adder 35
Multiplier by / 5, 37 is each delay circuit 31-33
Adder 38 adds 1 to the output of adder 37
A multiplier for multiplying by / 3, an adder 39 for adding the digital video signal PT and the outputs of the delay circuits 32, 34, 4
0 is a multiplier for multiplying the output of the adder 39 by 1/3.

If the pixel at a certain point in the digital image signal PT is P (x, y + 1) [where x ≠ 0,351], the output pixels of the delay circuits 31 to 34 are P respectively.
(X + 1, y), P (x, y), P (x-1, y), P
(X, y-1), which are adjacent to each other. Therefore, the multiplier 36 outputs the average value of five pixels adjacent to each other in the horizontal direction and the vertical direction centering on the pixel P (x, y) instead of the value of the pixel P (x, y). Become. By taking the average of the five pixels, the high frequency spatial frequency components in the horizontal and vertical directions are removed (attenuated) from the original P (x, y) pixel. In addition, from the multiplier 38, the pixel P (x, y)
The average value of three pixels adjacent to each other in the horizontal direction with respect to is output instead of the value of the pixel P (x, y),
The high spatial frequency components in the horizontal direction are removed. Further, the multiplier 40 outputs the average value of three vertically adjacent pixels centered on the pixel P (x, y) instead of the value of the pixel P (x, y), and High spatial frequency components in the direction are removed.

Reference numeral 50 denotes an input S ₁ from each of the multipliers 36, 38 and 40 of the spatial frequency filter 30 and the delay circuit 32.
Is a selector which selectively outputs one from among S ₄ to S ₄ and outputs the first to third select signals A from the above-described motion detection circuit 2, horizontal direction selection circuit 10 and vertical direction selection circuit 20. By selecting the input S _k according to the combination of C to C, the pixels in the vicinity of the block boundary in the image represented by the digital image signal PT are averaged with the surrounding pixels to remove the high spatial frequency component, The pixels other than the vicinity of the block are output as they are, and the digital image signal PT ′ is output. The correspondence relationship between the combination of the first to third select signals A to C and the output of the selector 50 is as shown in Table 1 below.

[0024]

[Table 1]

Next, the operation of the above embodiment will be described with reference to FIG. FIG. 4 is an operation explanatory diagram of the spatial frequency filter 30 and the selector 50. For convenience of explanation, the decoder 1
Let the current pixel of the digital image signal PT output from P (x, y + 1). The pixel position of the digital image signal PT decoded by the decoder 1 is P (0,0), P
(1,0), P (2,0), ..., P (231,0),
P (0,1), P (2,0), ..., P (231,
1), ..., P (x, y + 1), the motion detection circuit 2 always selects the first select signal A indicating the presence or absence of motion of the pixel P (x, y) delayed by one line from the digital image signal PT. The horizontal direction selection circuit 10 outputs the pixel P (x, y) which is always delayed by one line from the current pixel P (x, y + 1) of the digital image signal PT immediately after the vertical boundary line on the left side of the block. A second select signal B indicating whether the right side or the right side of the vertical boundary line is immediately left is output, and the vertical direction selection circuit 20 outputs the pixel P (x, y +) of the digital image signal PT.
A third select signal C indicating whether or not the position of the pixel P (x, y) always delayed by one line from 1) is immediately below the upper horizontal boundary line or immediately above the lower horizontal boundary line. Is output.

On the other hand, the delay circuit 32 of the spatial frequency filter 30 outputs a pixel which is simply delayed by one line from the digital image signal PT, and delays when the current pixel of the digital image signal PT is P (x, y + 1). Circuit 32
Is the pixel P (x, y). When the motion detection circuit 2 outputs the L-level first select signal A indicating that the pixel P (x, y) has no motion, the selector 50 selects S ₄ input from the delay circuit 32. Since there is no motion for all pixels in one frame, the selector 50 outputs the digital image signal PT.
Image signal PT 'which is delayed by one line
Is output and the resolution does not deteriorate.

When the H level first select signal A indicating that the pixel P (x, y) has a motion is output from the motion detecting circuit 2, the selector 50 outputs the second and third select signals B, According to the combination of C, one of S _{1 to} S ₃ input from the multipliers 36, 38 and 40 is selected and output according to Table 1. As shown in FIG. 4, assuming that the pixel P (x, y) is contained in the block B (i, j),
When the x coordinate of the pixel P (x, y) is 16i, which is immediately to the right of the left vertical boundary of block B (i, j), or 16i + 15, which is immediately to the left of the right vertical boundary, horizontal selection circuit 10 Outputs H level, and 16i + 1 to 16i +
During 14 the L level is output. On the other hand, the pixel P (x,
When the y coordinate of y) is 16j which is immediately below the upper horizontal boundary line of block B (i, j) or 16j + 15 which is immediately above the lower horizontal boundary line, the vertical direction selection circuit 20 is at the H level. Is output, and L is output between 16j + 1 to 16j + 14.
Output level.

Therefore, P (x, y) is the block B (i,
j) is the corner x = 16i, y = 16j, x = 1
6i + 15, y = 16j, x = 16i, y = 16j + 1
5, x = 16i + 15, y = 16j + 15 (see P _{1 to} P _{4 in} FIG. 4), the second and third select signals B and C both become H level, and the first select signal A
Is also at the H level, the selector 50 selects the input S ₁ from the multiplier 36. As a result, when the pixel P (x, y) of the original digital image signal PT is any _{one of the} target pixels P _{1 to} P ₄ , there is a possibility that the target pixels have a certain amount of motion and block distortion is conspicuous. If so, the pixel value obtained by replacing the pixel of interest with the average value of five pixel values including the pixel of interest and four pixels adjacent to each other in the horizontal and vertical directions with the pixel of interest sandwiched is output. The high spatial frequency components in the vertical and vertical directions are removed, and the block distortion at the corners of the blocks becomes inconspicuous.

Further, when P (x, y) is other than P _{1 to} P ₄ , it is on the right side of the left vertical boundary line of the block B (i, j) or on the left side of the right vertical boundary line, x = 16i, y = 16
j + 1 to 16j + 14, x = 16i + 15, y = 16j
In the case of +1 to 16j + 14 (see P ₅ and P _{6 in} FIG. 4),
If the second select signal B is at H level, the third select signal C is at L level, and the first select signal A is also at H level, the selector 50 selects the input S ₂ from the multiplier 38. As a result, the pixel P of the original digital image signal PT
(X, y) is the pixel of interest P ₅ (x = 16i, y = 16j +
1 to 16j + 14) or the target pixel P ₆ (x
= 16i + 15, y = 16j + 1 to 16j + 14), if there is a possibility that block distortion is conspicuous due to a certain amount of movement of these target pixels, they are adjacent to the target pixel in the horizontal direction across the target pixel. Since the pixel value in which the pixel of interest is replaced with the average value of the three pixel values including two pixels is output, the horizontal high frequency spatial frequency component that crosses the vertical boundary line of the block B (i, j) is To be removed. Therefore,
The vertical boundary of the block B (i, j) becomes inconspicuous.

Further, P (x, y) is other than P _{1 to} P ₄ and is immediately below the upper horizontal boundary line of the block B (i, j) or immediately above the lower horizontal boundary line. x = 16i + 1 to
16i + 14, y = 16j, x = 16i + 1 to 16i +
14, y = 16j + 15 (see P ₇ and P _{8 in} FIG. 4), if the second select signal B is L level, the third select signal C is H level, and the first select signal A is also H level, the selector 50 selects the input S ₃ from the multiplier 40. As a result, the pixel P (x, y) of the original digital image signal PT becomes the target pixel P ₇ (x = 16i + 1 to 16i).
+14, y = 16j) or the target pixel P
₈ (any of x = 16i + 1 to 16i + 14, y = 1
6j + 15), if there is a possibility that there is a certain amount of movement in these target pixels and block distortion is conspicuous, the target pixel and two pixels vertically adjacent to each other with the target pixel sandwiched are included. Since the pixel value obtained by replacing the pixel of interest with the average value of the two pixel values is output, the vertical high frequency spatial frequency component that crosses the horizontal boundary line of the block B (i, j) is removed. Therefore, the horizontal boundary of the block B (i, j) becomes inconspicuous.

The pixel P (x, of the digital image signal PT
y) exists inside the block B (i, j) instead of near the boundary, and x = 16i + 1 to 16i + 14, y = 16j + 1.
In the case of ˜16j + 14 (see pixel P _{9 of} interest), both the second and third select signals B and C are at L level. In this case, since the selector 50 selects the input S ₄ from the delay circuit 32 regardless of the level of the first select signal A, the pixel P (x, y) of the digital image signal PT is output as it is. , It is possible to avoid the deterioration of the resolution inside the block. Even if the pixel P (x, y) is near the boundary of the block B (i, j) and either or both of the second select signal B and the third select signal C are at the H level, the pixel P (x, y) There is no movement in (x, y),
The first select signal A output from the motion detection circuit 2 is L
If it is a level, the selector 50 selects the input S ₄ from the delay circuit 32, so that the pixel P (x, y) of the digital image signal PT is output as it is, and the resolution near the block boundary is unnecessary. It is avoided that it deteriorates.

According to this embodiment, in the image represented by the digital image signal PT after being decoded by the decoder 1, the pixels in the vicinity of the block boundary are selected by the horizontal direction selecting circuit 10 and the vertical direction selecting circuit 20, and the frame is also selected. Pixels that have changed by a certain amount or more between them are detected by the motion detection circuit 2. Then, by the spatial frequency filter 30 and the selector 50, with respect to the image after decoding, in the pixels near the block boundary,
In addition, a high spatial frequency component is removed from a pixel having a large change between frames, and an image in which other pixels are left unchanged is created and output as a digital image signal PT ′. As a result, it is possible to suppress block distortion at a block boundary, which is particularly noticeable in a frame with large motion, while avoiding deterioration of resolution within the block. On the other hand, a good resolution can be maintained over the entire frame for a frame with no motion or a small frame, and when there is motion in only a part of the frame, the block is blocked while avoiding deterioration of the resolution within the block for that region. The block distortion at the boundary can be made inconspicuous, and other areas with no motion or small motion can be kept at good resolution.

Further, the removal of the high spatial frequency components of the pixels near the vertical boundary line of the block excluding the corners of the block is performed by averaging the pixel of interest in the decoded image and the pixels adjacent in the horizontal direction, Since it is replaced with pixels, it is possible to remove high frequency spatial frequency components with a simple configuration.
Also, since averaging (removal of high spatial frequency components in the vertical direction) of vertically adjacent pixels, which is unrelated to the reduction of block distortion at the vertical boundaries of blocks, is not performed, the vertical boundaries of blocks are It is possible to avoid deterioration of the resolution in the vertical direction near the line. On the contrary, the removal of the high spatial frequency components of the pixels in the vicinity of the horizontal boundary line of the block excluding the corners of the block is performed by averaging the pixel of interest and vertically adjacent pixels in the decoded image, and Since the replacement is performed, the high spatial frequency components can be removed with a simple structure, and the averaging (horizontal averaging) of horizontally adjacent pixels, which is unrelated to the reduction of block distortion at the horizontal boundary line, can be performed. Direction high frequency spatial frequency components are not removed), it is possible to avoid deterioration of the horizontal resolution near the horizontal boundary line of the block.

[0034] In the embodiment described above, among the pixels around the block boundary, the removal of the average high frequency components taking the P ₁ to P ₄ only pixels adjacent in the horizontal direction and the vertical direction in FIG. 4 However, even in the case of P _{5 to} P ₈ , the high frequency components may be removed by averaging the pixels adjacent in the horizontal and vertical directions. Also, for pixels near the block boundary that do not change more than a certain amount between frames, the high spatial frequency component is not removed, but the pixel value changes between frames. Regardless of whether or not, the high spatial frequency component may be unconditionally removed as long as it is a pixel near the block boundary line. In this case, the motion detection circuit 2 is omitted, and the selector 50 selects _one of the inputs S _{1 to} S ₄ according to the following table 2 according to the combination of the second and third select signals B and C.
You can select one and output it.

[0035]

[Table 2]

Further, in the above-described embodiment, the block distortion is applied to the image obtained by decoding the hybrid-encoded image data by combining the inter-frame predictive encoding and the intra-frame DCT encoding. Although the case of reducing is described as an example, the present invention is not limited to this, and predictive coding between fields and DCT coding within fields are combined to decode hybrid-coded image data. For the obtained image, block distortion can be similarly removed by replacing the 1-frame delay circuit 3 in FIG. 1 with a 1-field delay circuit and replacing the frame clock FCK with a field clock.

The image coding method is not limited to hybrid coding in which intraframe coding or intrafield coding by DCT and interframe predictive coding or interfield predictive coding are combined, and the Hadamard transform is performed. Intra-frame coding or intra-field coding by other orthogonal transform coding such as, and dividing the frame or field into blocks based on the block matching method,
It may be a combination of other coding methods such as frame prediction coding with motion compensation (MC) or motion prediction (MC) with field prediction coding for performing motion detection in block units. Also, only intraframe coding or intrafield coding by orthogonal transform coding such as DCT or Hadamard transform, or frame prediction coding with motion compensation (MC) or field prediction coding with motion compensation (MC) is performed. Only interframe coding or interfield coding may be performed. The point is that the frame or field is divided into blocks and the coding process is performed in block units. Block distortion can be reduced for an image decoded by the decoding method described above.

Further, although the above embodiment has been described by taking a monochrome image as an example, the present invention is not limited to this. For example, even if it is a color image, R, G,
Block distortion can be reduced by performing the same processing as in the above-described embodiment for each B.

[0039]

According to the image processing apparatus of the present invention, the pixels near the block boundary line are selected from the decoded image, and the high spatial frequency of the pixel near the block boundary line is selected for the decoded image. Since the components are removed and the other pixels are left as they are, the block distortion at the block boundary can be made inconspicuous while avoiding the deterioration of the resolution within the block.

According to another image processing apparatus of the present invention, a pixel having a large change between frames or fields is detected in the image after decoding, and a pixel near the block boundary line is detected in the image after decoding. And, the high spatial frequency component is removed for the pixel whose change between frames or fields is large,
Since the other pixels are left as they are, it is possible to make the block distortion at the block boundary line inconspicuous while avoiding the deterioration of the resolution in the block for the frame or field with large motion. Or for the field, good resolution can be maintained over the entire frame or field.

According to still another image processing apparatus of the present invention,
The removal of the high frequency spatial frequency component is performed by averaging the pixels around the pixel of interest in the decoded image and replacing it with the pixel of interest. Therefore, it is possible to remove the high frequency spatial frequency component with a simple configuration. it can.

According to another image processing apparatus of the present invention, the high frequency spatial frequency component in the horizontal direction is removed from the pixels near the vertical block boundary line, and the pixels in the vertical direction are removed from the pixels near the horizontal block boundary line. Since the high spatial frequency component is removed, the block distortion can be made inconspicuous while minimizing the deterioration of resolution near the block boundary line.

According to another image processing apparatus of the present invention, the removal of high spatial frequency components in the horizontal direction is performed by averaging the pixels in the horizontal direction around the pixel of interest in the decoded image and replacing the pixel with the pixel of interest. The removal of the high frequency spatial frequency components in the vertical direction is performed by averaging the pixels in the vertical direction around the pixel of interest in the image after decoding and replacing them with the pixel of interest.
It is possible to remove horizontal high frequency spatial frequency components and vertical high frequency spatial frequency components with a simple configuration.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between a digital image signal output from a decoder and various clocks.

FIG. 3 is an explanatory diagram showing a block size and a positional relationship in a frame.

FIG. 4 is an explanatory diagram showing operations of a spatial frequency filter and a selector.

[Explanation of symbols]

1 Decoder 2 Motion Detection Circuit 10 Horizontal Direction Selection Circuit 20 Vertical Direction Selection Circuit 30 Spatial Frequency Filter 50 Selector

Claims (5)

[Claims] 1. An image processing apparatus comprising a decoding means for dividing a frame or field into a large number of blocks and decoding an image coded in each block, wherein a pixel in the vicinity of a block boundary line in the decoded image. And a high-frequency spatial frequency component removing means for removing the high-frequency spatial frequency components of the pixels near the block boundary selected by the selection means from the decoded image and leaving the other pixels unchanged. An image processing apparatus characterized by being provided. 2. A detection means for detecting a pixel having a large change between frames or between fields in a decoded image is provided, and the high spatial frequency component removing means is
High spatial frequency components are removed from the pixels in the vicinity of the block boundary line that have been selected by the selection means and that have a large change between frames or fields detected by the detection means, and other pixels remain unchanged. The image processing apparatus according to claim 1, wherein: 3. The removal of the high spatial frequency component by the high spatial frequency component removing means is performed by averaging pixels around the pixel of interest in the image after decoding and replacing them with the pixel of interest. The image processing device according to item 1 or 2. 4. The removal of the high spatial frequency component by the high spatial frequency component removing means removes the high spatial frequency component in the horizontal direction from the pixels in the vicinity of the vertical block boundary, and removes the horizontal spatial frequency component in the vicinity of the horizontal block boundary. The image processing apparatus according to claim 1 or 2, wherein the high spatial frequency component in the vertical direction is removed from the pixel in (1). 5. The removal of horizontal high frequency spatial frequency components by the high frequency spatial frequency component removing means is performed by averaging horizontal pixels around the pixel of interest in the image after decoding and replacing them with the pixel of interest. The image processing apparatus according to claim 4, wherein the removal of the high spatial frequency component in the vertical direction is performed by averaging the pixels in the vertical direction around the pixel of interest in the image after decoding and replacing the pixel with the pixel of interest. .