IMAGE PROCESSING APPARATUS, IMAGE PROCESSING METHOD, AND STORAGE MEDIUM

• US 20140226905A1
• Filed: 02/05/2014
• Published: 08/14/2014
• Est. Priority Date: 02/14/2013
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Yahata, Kazuhiro, Sasaki, Yoshitaka
• Granted Patent: US 9,384,531 B2
• Time in Patent Office: Days
• US Class Current: 382/194
• CPC Class Codes: G06F 18/22 Matching criteria, e.g. proximity measures
• CPC Class Codes: G06T 2207/20012 Locally adaptive
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing

Abstract

A non-local means method is insufficient in its noise reduction effect or edge retainability due to a perfect match between blocks in a case where a reference pixel matches a target pixel. Therefore, information on a target region and plural reference regions is obtained for the target pixel. Whether the target region matches any one of the reference regions is determined from the obtained information. Switching between weight derivation methods based on similarity between the target region and the reference region is performed according to a determined result.

Claims

1. An image processing apparatus for determining a pixel value of a target pixel by a weighted mean of a plurality of reference pixels in image data, comprising:

a derivation unit configured to derive a weight for each of the reference pixels, based on similarity between a target region associated with the target pixel and a reference region associated with the reference pixels; and

a weighted mean processing unit configured to perform weighted mean processing based on pixel values of the plurality of reference pixels and the weights corresponding to the reference pixels, respectively, derived by the derivation unit,

wherein the weighted mean processing unit performs the weighted mean processing by using a pixel other than the target pixel as the reference pixel.

2. The image processing apparatus according to claim 1, further comprising a setting unit configured to set a group of reference pixels near the target pixel containing the target pixel, as a reference pixel group,

wherein the derivation unit derives the similarity by using a pixel contained in the reference pixel group set by the setting unit, as the reference pixel,

wherein the weighted mean processing unit performs the weighted mean processing by using the pixel other than the target pixel as the reference pixel, by replacing a weight derived corresponding to the target pixel, or the product of the pixel value of the target pixel and a corresponding weight, with a predetermined value.

3. The image processing apparatus according to claim 1, wherein the image processing apparatus performs noise reduction on the image data by a non-local means method.

4. The image processing apparatus according to claim 1, wherein the target region and the reference region have the same pixel arrangement.

5. The image processing apparatus according to claim 1, further comprising a determining unit configured to determine whether a reference pixel having a high degree of the similarity is present,

wherein, in a case where the determining unit determines that the reference pixel having the high similarity is absent, the derivation unit derives a weight for the target pixel, and the weighted mean processing unit determines the pixel value of the target pixel according to the value of the target pixel, the value of the reference pixel, and the weight for each pixel.

6. The image processing apparatus according to claim 5, wherein the determining unit makes the determination based on similarity of each reference region.

7. An image processing apparatus comprising:

an obtaining unit configured to obtain information on each pixel of a target region associated with a target pixel, and information on each pixel of a reference region associated with reference pixels, in image data;

a determining unit configured to determine whether the reference pixel is the same pixel as the target pixel, from the information obtained by the obtaining unit;

a derivation unit configured to derive a weight according to similarity between the target region and the reference region according to a result determined by the determining unit; and

a decision unit configured to decide a pixel value of the target pixel according to the weight and a pixel value of the reference pixel.

8. The image processing apparatus according to claim 7, wherein, in a case where the target pixel is used as the reference pixel, the derivation unit performs switching between derivation methods so as to derive a weight for the target pixel by a different method from that in a case where the target pixel and the reference pixel are not the same.

9. The image processing apparatus according to claim 8, wherein, in a case where the determining unit determines that she target pixel matches the reference pixel, the derivation unit derives a preset value as a weight for the reference pixel as the target pixel.

10. The image processing apparatus according to claim 9, wherein the preset value is an expected value of the weight in a case where a pixel value of the target region and a pixel value of the reference region match each other except for noise.

11. The image processing apparatus according to claim 9, wherein the preset value is equal to or more than 0 and is 5 or less times the expected value of the weight in a case where the pixel value of the target region and the pixel value of the reference region match each other except for noise.

12. The image processing apparatus according to claim 7, wherein the derivation unit is specified so as to set small a relative difference between a weight in a case where the target pixel matches any one of the reference pixels and a weight derived by the following equation in a case where the target pixel does not match the reference pixel:

13. An image processing apparatus comprising:

a derivation unit configured to derive a weight for a reference pixel by using a weight function according to a difference between a pixel value of each pixel in a target region associated with a target pixel and a pixel value of each pixel in a reference region associated with a reference pixels, in image data; and

a decision unit configured to decide the pixel value of the target pixel based on the weight and the pixel value of the reference pixel,

wherein the weight function is such that a weight in a case where the sum of the differences is 0 is not a sole maximum value.

14. The image processing apparatus according to claim 13, wherein the weight function is such that a weight for a reference pixel which forms the reference region where the pixel value of the target region and the pixel value of the reference region cannot be considered to match each other except for noise has a sufficiently small value.

15. An image processing apparatus for determining a pixel value of a target pixel by a weighted mean of a plurality of reference pixels in image data, comprising:

a derivation unit configured to derive a weight for each of the reference pixels, based on similarity between a target region associated with the target pixel and a reference pixel region associated with the reference pixels; and

a weighted mean processing unit configured to perform weighted mean processing based on pixel values of the plurality of reference pixels and the weights corresponding to the reference pixels, respectively, derived by the derivation unit,

wherein the derivation unit sets a weight corresponding to the target pixel itself by reducing the weight according to the similarity obtained in a case where the target pixel itself is used as the reference pixel.

16. An image processing method for determining a pixel value of a target pixel by a weighted mean of a plurality of reference pixels in image data, comprising:

a derivation step of deriving a weight for each of the reference pixels, based on similarity between a target pixel region associated with the target pixel and a reference pixel region associated with the reference pixels; and

a weighted mean processing step of performing weighted mean processing based on pixel values of the plurality of reference pixels and the weights corresponding to the reference pixels, respectively, derived by the derivation step,

wherein the weighted mean processing step performs the weighted mean processing by using a pixel other than the target pixel as the reference pixel.

20. A non-transitory computer readable storage medium storing a program which causes a computer to perform the image processing method according to claim 16.

17. An image processing method comprising:

an obtaining step of obtaining information on each pixel of a target region associated with a target pixel, and information on each pixel of a reference region associated with reference pixels, in image data;

a determining step of determining whether the reference pixel is the same pixel as the target pixel, from the information obtained by the obtaining step;

a derivation step of deriving a weight according to similarity between the target region and the reference region according to a result determined by the determining step; and

a decision step of deciding a pixel value of the target pixel according to the weight and a pixel value of the reference pixel.

18. An image processing method comprising:

a derivation step of deriving a weight for a reference pixel by using a weight function according to a difference between a pixel value of each pixel in a target region associated with a target pixel and a pixel value of each pixel in a reference region associated with reference pixels, in image data; and

a decision step of deciding the pixel value of the target pixel based on the weight and the pixel value of the reference pixel,

wherein the weight function is such that a weight in a case where the sum of the differences is 0 is not a sole maximum value.

19. An image processing method for determining a pixel value of a target pixel by a weighted mean of a plurality of reference pixels in image data, comprising:

a derivation step of deriving a weight for each of the reference pixels, based on similarity between a target region associated with the target pixel and a reference region associated with the reference pixels; and

a weighted mean processing step of performing weighted mean processing based on pixel values of the plurality of reference pixels and the weights corresponding to the reference pixels, respectively, derived by the derivation step,

wherein the derivation step sets a weight corresponding to the target pixel itself by reducing the weight according to the similarity obtained in a case where the target pixel itself is used as the reference pixel.