Image processing apparatus, image processing method, and storage medium for reducing noise in a captured image

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 processor and a memory storing instructions which, when executed by the processor, cause the processor to function as:

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 by calculating a sum of products of 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 derives a weight for the target pixel to be used for the sum of products calculated by the weighted mean processing unit as 0, and

the weighted mean processing unit calculates a result of the weighted mean processing using the sum of products by using the weights derived by the derivation unit.

2. The image processing apparatus according to claim 1 , wherein the instructions further cause the processor to function as 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, and

wherein the weighted mean processing unit calculates the sum of products after replacing the weight derived corresponding to the target pixel with a 0.

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 ,

wherein the derivation unit inputs pixel values of pixels in the target region including the pixel value of the target pixel and pixel values of pixels in the reference regions corresponding to all reference pixels and outputs each weight corresponding to each reference pixel, and

wherein the weighted mean processing unit inputs each weight corresponding to each reference pixel and 0 as the weight of the target pixel.

6. The image processing apparatus according to claim 1 , wherein the instructions further cause the processor to function as a setting unit configured to set a pixel to be processed on the weighted mean processing, wherein the setting unit does not set the target pixel as the pixel to be processed on the weighted mean processing and sets pixels near the target pixel other than the target pixel as the reference to be processed on the weighted mean processing, whereby, the weighted mean processing unit performs the weighted mean processing in which the weight for the target pixel in the sum of products is 0.

7. The image processing apparatus according to claim 6 ,

wherein the setting unit determines whether both the target pixel and the pixels near the target pixel are set as the reference pixel to be processed on the weighted mean processing or pixels only near the target pixel as the reference pixel to be processed on the weighted mean processing, and

wherein the weighted mean processing unit switches the weighted mean processing between the weighted mean processing including the pixel value of the target pixel and the weighted mean processing not including the pixel value of the target pixel.

8. The image processing apparatus according to claim 7 , wherein the setting unit performs the determination based on a number of reference pixels having similarity satisfying a predetermined condition.

9. The image processing apparatus according to claim 1 , wherein the instructions further cause the processor to function as 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, and

wherein the weighted mean processing unit calculates the sum of products after replacing a product of the pixel value of the target pixel and a corresponding weight, with a 0.

10. The image processing apparatus according to claim 1 , wherein each pixel in the image data is set as the target pixel in a preset order.

11. 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 processor and a memory storing instructions which, when executed by the processor, cause the processor to function as:

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;

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

a determining unit configured to determine whether or not the similarity for each reference pixel indicates that each reference pixel is similar to the target pixel,

the weighted mean processing unit calculates a result of the weighted mean processing using the sum of products by using the weights derived by the derivation unit, and

wherein, in a case where the determining unit determines that the reference pixel having the similarity indicating the reference pixel is similar to the target pixel is absent, the derivation unit derives a value larger than 0 as the weight for the target pixel, and in a case where the determining unit determines that the reference pixel having the similarity indicating that the reference pixel is similar to the target pixel is present, the derivation unit derives the weight for the target pixel to be used for the sum of products calculated by the weighted mean processing unit as 0.

12. The image processing apparatus according to claim 11 , wherein the determining unit makes the determination based on similarity of each reference region.

13. 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 by calculating a sum of products of 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 includes deriving a weight for the target pixel to be used for the sum of products calculated by the weighted mean processing step as 0, and the weighted mean processing step includes calculating a result of the weighted mean processing using the sum of products by using the weights output from the derivation step.

14. A non-transitory computer readable storage medium storing a program which causes a computer to perform 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, the image processing method 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 by calculating a sum of products of 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 includes deriving a weight for the target pixel to be used for the sum of products calculated by the weighted mean processing step as 0, and the weighted mean processing step includes calculating a result of the weighted mean processing using the sum of products by using the weights output from the derivation step.

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 processor and a memory storing instructions which, when executed by the processor, cause the processor to function as:

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 without the pixel value of the target pixel,

wherein the pixel value output from the weighted mean processing unit is equivalent to a value expressed by the following equation:

Σ j NR w ij I j /Σ j NR w ij

wherein Ij denotes pixel value of reference pixel, wij denotes the weight corresponding to the reference pixel, j denotes are indices j which identify plural reference pixels, Nr denotes the number of reference pixels, and

wherein a result expressed by symbol Σ, which is a sum of all result of product values of the weights and the pixel values, does not include a product value of the weight corresponding to the target pixel and the pixel value of the target pixel.

16. 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 a 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, under a condition that if a pixel X 2 in the image data is the target pixel, a pixel X 1 in the image data is positioned on the reference pixel,

in a case where the pixel X 1 is the target pixel, the derivation unit derives the weight for the pixel X 1 as 0, and

in a case where the pixel X 2 is the target pixel,

if the similarity of the pixel X 1 indicates that the pixel X 1 is similar to the pixel X 2 , the derivation unit derives the weight for the pixel X 1 used for a result of the weighted mean processing for the pixel X 2 as a predetermined value larger than 0, and

if the similarity of the pixel X 1 indicates that the pixel X 1 is not similar to the pixel X 2 , the derivation unit derives the weight for the pixel X 1 used for a result of the weighted mean processing for the pixel X 2 as a smaller than or equal to the predetermined value.

17. The image processing apparatus according to claim 16 , wherein each pixel in the image data is set as the target pixel in a preset order.