JP2001245155A - Method for edge correction of image data, and device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve the problems where even through deblocking filter and delinking filter can reduce block noise but cannot sufficiently correct shape of edge of image data. SOLUTION: In an method for edge correcting of image data, that method is used to output an inputted image data through compression and decompression, a noted pixel is determined as to whether it is an edge pixel, according to the change in the pixel value of peripheral pixel of the interest pixel, and if the noted pixel is an edge pixel, the direction is detected to minimize the change of pixel value of the peripheral pixel, the pixel value, which is calculated by the average of the pixel value in this direction and by the gradient of the pixel value of the location of the interest pixel, is determined as the new pixel value for the noted pixel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting distortion of the shape of an edge generated in image data by compression encoding.
And its device.

[0002]

2. Description of the Related Art An image encoded by DCT (Discrete Cosine Transform) such as JPEG or MPEG has a problem that block noise and mosquito noise are generated at a high compression ratio. Techniques for reducing compression distortion include, for example, "ISO / IEC
JTC1 / SC29 / WG11 MPEG97 / N1796: MPEG-4 Video Verifica
There is a deblocking filter and a deringing filter described in "Action Model Version 8.0".

[0003]

However, in the deblocking filter and the deringing filter, although the block noise and the mosquito noise are reduced, there still remains a problem that the contour shape is not sufficiently corrected.

There is a median filter as a filter having an effect of correcting the contour shape. However, the image is flattened because the directionality of the edge is not taken into account and the filtering is performed on pixels other than the edge. There was a problem that sometimes it was too long.

Further, there is an image enlarging method in consideration of avoiding the distortion of the contour shape accompanying the image enlargement, but it is not intended to correct the contour shape itself.

It is conceivable to perform high-frequency enhancement on an image after distortion reduction in order to eliminate blur, but there is a problem in that even reduced distortion is enhanced.

[0007]

According to a first aspect of the present invention, there is provided an image data edge correction method for compressing / decompressing and outputting input image data. Of the pixels of the above, based on the change in the pixel value of the pixel located near the pixel of interest,
It is determined whether or not the pixel of interest may be regarded as an edge pixel, and when the pixel of interest is regarded as an edge pixel, a direction in which a change in the pixel value of a pixel located near the pixel of interest is minimized Is detected, and an average value of the pixel values in that direction, or a pixel value calculated from the average value and a gradient of the pixel value at the pixel position of interest is set as a new pixel value of the pixel of interest.

According to a second aspect of the present invention, in the first aspect of the present invention, a pixel located in the vicinity of the pixel of interest is K × K (K : Natural number).

According to a third aspect of the present invention, there is provided the image data edge correction method according to any one of the first and second aspects, wherein a change in a pixel value of a pixel located in the vicinity of the pixel of interest is determined by It is obtained based on the pixel value differences in the horizontal direction, the vertical direction, the diagonally right direction, and the diagonally left direction centering on the target pixel.

According to a fourth aspect of the present invention, there is provided an image data edge correction method used for compressing and restoring input image data and outputting the compressed image data.
Of the image data, K × K (K:
A natural number), a pixel value difference in the horizontal direction and the vertical direction is calculated for the pixels belonging to the range, and as a result of the first process, the pixel value difference in the horizontal direction and the vertical direction sets a threshold value. If it exceeds, K × K including the pixel of interest is included.
(K: natural number) A second process of calculating a pixel value difference in the diagonal right and diagonal directions for the pixels belonging to the range of the natural number, and the horizontal direction, the vertical direction, the diagonal right direction, and the diagonal left direction A third process of calculating the minimum value among the pixel value differences in the directions, and an average value of the pixel values of K (K: natural number) pixels arranged in the direction of the minimum value as a result of the third process. And calculating the average value of the pixel values in that direction as a new pixel value of the pixel of interest.

According to a fifth aspect of the present invention, there is provided the image data edge correcting method according to any one of the first and fourth aspects, wherein the image data is either still image data, moving image data, or both. It is characterized by being one or the other.

According to a sixth aspect of the present invention, there is provided an image data edge correcting apparatus for compressing and restoring input image data and outputting the compressed image data.
It is determined whether or not the target pixel may be regarded as an edge pixel based on a change in the pixel value of a pixel located in the vicinity of the target pixel among the pixels of the image data. When considered as a pixel, a direction in which a change in pixel value of a pixel located in the vicinity of the pixel of interest is minimized is detected,
An average value of pixel values in that direction, or a pixel value calculated from the average value and a gradient of a pixel value at a pixel position of interest is set as a new pixel value of the pixel of interest.

According to a seventh aspect of the present invention, in the invention according to the sixth aspect, a pixel located in the vicinity of the pixel of interest includes K × K (K : Natural number).

According to an eighth aspect of the present invention, there is provided the image data edge correction apparatus according to any one of the sixth and seventh aspects, wherein the change in the pixel value of the pixel located in the vicinity of the pixel of interest is determined by It is obtained based on the pixel value differences in the horizontal direction, the vertical direction, the diagonally right direction, and the diagonally left direction centering on the target pixel.

According to a ninth aspect of the present invention, there is provided an image data edge correcting apparatus for compressing and restoring input image data and outputting the compressed image data.
An image data input unit for inputting image data, and a horizontal direction, a vertical direction, a diagonal direction, and a pixel range including a pixel of interest and belonging to a range of K × K (K: natural number). An edge determining unit that calculates a pixel value difference in the diagonal left direction; and a minimum (K: natural number) pixel that is arranged in the direction of the minimum value among the pixel value differences calculated by the edge determining unit. A gradient direction pixel selection unit and a new pixel that calculates an average value of pixel values of the pixels selected by the minimum gradient direction pixel selection unit, or a pixel value calculated from the average value and the gradient of the pixel value at the pixel position of interest The image processing apparatus further includes a value calculation unit, and an image data output unit that outputs the pixel value calculated by the new pixel value calculation unit as a new pixel value of the pixel of interest.

According to a tenth aspect of the present invention, there is provided the image data edge correcting apparatus according to the ninth aspect, wherein the image data is either still image data or moving image data, or any one of them. Features.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an apparatus for performing edge correction of image data for realizing the present invention.

As shown in FIG. 1, an image data input unit 10
1 is input to the minimum gradient direction pixel selection unit 105 via the edge determination unit 103 and the switching unit 104, using, for example, all image data (still image data and moving image data) input from the JPEG decoder 100 as input pixel values. I do. The edge determination unit 103 determines whether or not the pixel of interest can be regarded as an edge pixel in all the image data. If it is determined that the pixel of interest can be regarded as an edge pixel, switching is performed. The unit 104 is switched to the minimum gradient direction pixel selection unit 105 side, and the minimum gradient direction pixel selection unit 105 side minimizes the change (gradient) of the input pixel value in the horizontal direction, the vertical direction, the diagonal right direction, and the diagonal left direction. The pixel value data in the minimum direction is sent to the new pixel value calculation unit 106, and the new pixel value calculation unit 106 calculates the arithmetic average value of those pixel values or the average value A new pixel value is calculated from the gradient of the pixel value. The image data output unit 107 replaces the image data processed by the new pixel value calculation unit 106 with a new pixel value of the pixel of interest, and outputs the image data to the image data display unit 108 as an output image.

Here, the processing steps of the apparatus shown in FIG. 1 will be described with reference to the flowchart of FIG.

In FIG. 2, the vertical position j of the target pixel among the target pixel positions (i, j) is set to "0" (step 20).
1) Also, the horizontal position i of the target pixel among the target pixel positions (i, j) is set to “0” (step 2011).

Next, as shown in FIG. 3 (a), a pixel value difference d1 for a pixel in the horizontal direction centering on the target pixel position (i, j) and a target pixel position (i, j) Then, a pixel value difference d2 is calculated for a pixel in the vertical direction with respect to (step 202). Specifically, the horizontal pixel value difference d1 = | X (i-1, j) -X (i + 1,
j) | Pixel value difference d2 = | X (i, j-1) -X (i, j +
1) Calculate |.

The magnitude relationship between the horizontal pixel value difference d1 and the first threshold value (Th1) obtained in step 202 is compared, and the vertical pixel value difference d2 and the second threshold value (Th2) are compared. (Step 20)
3).

The pixel value difference d1 in the horizontal direction is larger than the first threshold value (Th1), or the pixel value difference d1 in the vertical direction is
If 2 (Th2) is greater than the second threshold (Th2), the process proceeds to step 205, and further, as shown in FIG. A pixel value difference d3 for the pixel of interest and a pixel value difference d4 for the pixel in the diagonally left direction about the pixel position of interest (i, j) are calculated (step 205). Specifically, the pixel value difference d3 in the oblique left direction d3 = | X (i-1, j-1) -X (i
+ 1, j + 1) | Pixel value difference d4 = | X (i + 1, j-1) -X (i
-1, j + 1) |

Of the horizontal pixel value difference d1 calculated in step 202, the vertical pixel value difference d2, the right diagonal pixel value difference d3 calculated in step 205, and the left diagonal pixel value difference d4, A minimum value is calculated (step 206).

An average value of the pixel values in the direction of the minimum gradient is obtained according to the minimum value obtained in step 206 (step 20).
7). In order to obtain a high-frequency emphasis effect at the edge, a new pixel value is calculated from the average value and the gradient of the pixel value at the pixel position of interest.

Specifically, if (d1 = dmin) Y (i, j) = (X (i-1, j) + X (i, j) + X (i + 1, j)) / 3+ L (X (i, j) -m1)… (1) else if (d2 = dmin) Y (i, j) = (X (i, j-1) + X (i, j) + X (i, j + 1)) / 3 + L (X (i, j) -m2)… (2) else if (d3 = dmin) Y (i, j) = (X (i-1, j-1) + X (i, j) + X (i + 1, j + 1)) / 3 + L (X (i, j) -m3)… (3) else if (d4 = dmin) Y (i, j) = ( X (i + 1, j-1) + X (i, j) + X (i-1, j + 1)) / 3 + L (X (i, j) -m4) ... (4) M1 = (X (i, j-1) + X (i, j + 1)) / 2… (5) m2 = (X (i-1, j) + X (i + 1, j)) / 2… (6) m3 = (X (i + 1, j-1) + X (i-1, j + 1)) / 2… (7) m4 = (X (i-1, j-1) + X (i + 1, j + 1)) / 2 (8).

However, dmin is a minimum value of d1 to d4, L is a real number equal to or greater than 0, and the greater the L, the greater the degree of high-frequency emphasis.

In the above equations (1) to (4), if it is not necessary to obtain a high-frequency edge emphasis effect, L = 0.
And it is sufficient.

On the other hand, if the following equation is applied in addition to the above-described equations (5) to (8), the effect of enhancing the high frequency range of the edge can be obtained. At this time, m1 = m2 = m3 = m4 = (X (i-1, j-1) + X (i, j-1) + X (i + 1, j-1) + X (i
-1, j) + X (i, j) + X (i + 1, j) + X (i-1, j + 1) + X (i, j + 1) + X (i + 1, j +
1) Calculate m1, m2, m3, and m4 by) / 9.

It is determined whether or not processing has been performed for the entire width of the image for i at the pixel position of interest (i, j) (step 208). If the process has not been performed on the entire width of the image, the process proceeds to step 209, where i
= I + 1, the process returns to step 202, and the above-described process is performed.

Finally, it is determined whether or not processing has been performed on the entire height of the image for j at the pixel position of interest (i, j) (step 210), and processing has been performed on the entire height of the image. If so, the process ends. If the process has not been performed on the entire height of the image, the process proceeds to step 211, where j = j
After performing the process with +1, the process returns to step 2011 to perform the above-described process.

Next, an example of the input pixel value and the output pixel value when the processing of FIG. 2 is performed is shown in FIGS.

In FIG. 4A, when the edge shape is distorted jaggedly, the level of the edge pixel is discontinuous. In this case, the minimum gradient direction is the edge direction (diagonal left direction). By replacing the value of the target pixel with the average value of the pixel values in this direction, the level of the edge pixel becomes continuous and the edge shape is corrected. You.

In FIG. 4B, when no edge exists near the pixel position of interest, pixels other than the edge are output with the original pixel values.

FIG. 5A shows a case where a term for high-frequency emphasis is added at L = 1 in step 207 of FIG. In this case, the edge is emphasized in addition to the correction of the edge shape.

In FIG. 5B, as in FIG. 4B, when there is no edge near the position of the pixel of interest, the pixel other than the edge is output with the original pixel value.

FIG. 6 shows an example in which an edge enhancement effect is obtained for a 5.times.5 pixel size. X in FIG.
When 1, X2, and X3 are the target pixel positions, the processing shown in FIG. 2 is performed on each of the target pixels.
The pixel values at the pixel positions Y1, Y2, and Y3 in FIG. 6B are replaced with new pixel values, and edge enhancement is performed.

Although the present invention has been described on the assumption that the pixel size is 3 × 3, 5 × 5, the present invention is not limited to this, and the present invention can be applied to the case where processing is performed on four or six or more pixels. Is possible.

[0040]

As is apparent from the above description, according to the present invention, it is possible to effectively correct the distortion of the edge shape with a simple configuration by one filtering and with a small amount of calculation.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an apparatus for performing edge correction of image data for realizing the present invention.

FIG. 2 is a flowchart in the present invention.

FIG. 3 is a pixel diagram near a pixel position of interest (i, j).

FIG. 4 is a schematic diagram illustrating the principle of edge correction.

FIG. 5 is a schematic diagram illustrating the principle of edge correction in a 3 × 3 pixel size.

FIG. 6 is a schematic diagram illustrating the principle of edge correction in a 5 × 5 pixel size.

[Explanation of symbols]

 100 JPEG decoder 101 Image data input unit 102 Input pixel value 103 Edge determining unit 104 Switching unit 105 Minimum gradient direction pixel selection unit 106 New pixel value calculation unit 107 Output pixel value 108 Image data display unit

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 5B057 CC03 CE02 CE03 CE06 5C021 PA53 PA56 PA57 PA58 PA62 PA66 RA02 RA07 RB08 XB03 5C077 LL19 PP03 PP05 RR21 5C078 CA22 DA02 9A001 BZ04 EE04 HH25 HH27 HH28 HH30 HZ24

Claims (10)

[Claims] 1. An image data edge correction method used when compressing and decompressing input image data and outputting the image data, wherein a change in a pixel value of a pixel located near a pixel of interest among pixels of the image data It is determined whether or not the target pixel may be regarded as an edge pixel based on the above.If the target pixel is regarded as an edge pixel, a change in the pixel value of a pixel located in the vicinity of the target pixel is determined. Detect the minimum direction,
An edge correction method for image data, wherein an average value of pixel values in the direction or a pixel value calculated from the average value and a gradient of a pixel value at a pixel position of interest is set as a new pixel value of the pixel of interest. . 2. The pixel according to claim 1, wherein the pixels located in the vicinity of the target pixel are pixels belonging to a range of K × K (K: natural number) including the target pixel. Edge correction method for image data. 3. A change in a pixel value of a pixel located in the vicinity of the target pixel is obtained based on pixel value differences in a horizontal direction, a vertical direction, a right diagonal direction, and a left diagonal direction centered on the target pixel. 3. The image data edge correction method according to claim 1, wherein: 4. An edge correction method for image data used when compressing and decompressing input image data and outputting the image data, wherein K × K (K:
A natural number), a pixel value difference in the horizontal direction and the vertical direction is calculated for the pixels belonging to the range, and as a result of the first process, the pixel value difference in the horizontal direction and the vertical direction sets a threshold value. If it exceeds, K × K including the pixel of interest is included.
(K: natural number) A second process of calculating a pixel value difference in the diagonal right and diagonal directions for the pixels belonging to the range of the natural number, and the horizontal direction, the vertical direction, the diagonal right direction, and the diagonal left direction A third process of calculating the minimum value among the pixel value differences in the directions, and an average value of the pixel values of K (K: natural number) pixels arranged in the direction of the minimum value as a result of the third process. Calculating the average value of the pixel values in the direction, and setting the average value of the pixel values in the direction as a new pixel value of the pixel of interest. 5. The image data edge correction method according to claim 1, wherein said image data is either still image data or moving image data or any one of them. 6. An image data edge correction apparatus used when compressing and decompressing input image data and outputting the image data, wherein a change in a pixel value of a pixel located near a pixel of interest among pixels of the image data It is determined whether or not the target pixel may be regarded as an edge pixel based on the above.If the target pixel is regarded as an edge pixel, a change in the pixel value of a pixel located in the vicinity of the target pixel is determined. Detect the minimum direction,
An edge correction apparatus for image data, wherein an average value of pixel values in the direction or a pixel value calculated from the average value and a gradient of a pixel value at a pixel position of interest is set as a new pixel value of the pixel of interest. . 7. The pixel according to claim 6, wherein the pixels located in the vicinity of the target pixel are pixels belonging to a range of K × K (K: natural number) including the target pixel. Image data edge correction device. 8. A change in pixel value of a pixel located in the vicinity of the pixel of interest is determined based on pixel value differences in a horizontal direction, a vertical direction, a diagonal right direction, and a diagonal left direction centering on the pixel of interest. 8. The image data edge correction device according to claim 6, wherein: 9. An image data edge correction apparatus used when compressing and decompressing and outputting input image data, comprising: an image data input unit for inputting image data; K × K (K:
An edge determining unit that calculates a pixel value difference in a horizontal direction, a vertical direction, a diagonal direction, and a left diagonal direction with respect to a pixel belonging to a range of (natural number), and among the pixel value differences calculated by the edge determining unit, A minimum gradient direction pixel selector for selecting K (K: natural number) pixels arranged in the direction of the minimum value, and an average value of the pixel values of the pixels selected by the minimum gradient direction pixel selector, or A new pixel value calculator for calculating a pixel value calculated from the average value and a gradient of the pixel value at the pixel position of interest; and outputting the pixel value calculated by the new pixel value calculator as a new pixel value for the pixel of interest. And an image data output unit. 10. The image data includes still image data,
The image data edge correction apparatus according to claim 9, wherein both or one of the moving image data is used.