IMAGE PROCESSING APPARATUS, IMAGE PROCESSING METHOD, AND PROGRAM

• US 20130051665A1
• Filed: 08/24/2012
• Published: 02/28/2013
• Est. Priority Date: 08/31/2011
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: SHINOZAKI, Hirotaka
• Granted Patent: US 8,891,866 B2
• Time in Patent Office: Days
• US Class Current: 382/167
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 5/00 Image enhancement or restoration
• CPC Class Codes: G06T 5/77 Retouching; Inpainting; Scratch removal
• CPC Class Codes: H04N 9/646 for image enhancement, e.g. vertical detail restoration, cross-colour elimination, contour correction, chrominance trapping filters

Abstract

Provided is an image processing apparatus including an image signal correction section that performs an image correction process. The image signal correction section performs a direction determination process of detecting a direction having a minimum pixel value gradient as a pixel value gradient direction in a pixel area including a target pixel; a defect detection process of calculating a Laplacian based on a pixel value of a reference pixel in a minimum gradient direction detected in the direction determination process with respect to the target pixel, and determining presence or absence of a defect of the target pixel; and a defect correction process of performing calculation of a corrected pixel value, which is obtained by applying the pixel value of the reference pixel in the direction detected in the direction determination process, with respect to a target pixel from which a defect has been detected in the defect detection process.

Claims

1. An image processing apparatus comprising:

an image signal correction section configured to perform an image correction process,

wherein the image signal correction section performs;

a direction determination process of detecting a direction having a minimum pixel value gradient as a pixel value gradient direction in a pixel area including a target pixel;

a defect detection process of calculating a Laplacian based on a pixel value of a reference pixel in a minimum gradient direction detected in the direction determination process with respect to the target pixel, and determining presence or absence of a defect of the target pixel; and

a defect correction process of performing calculation of a corrected pixel value, which is obtained by applying the pixel value of the reference pixel in the direction detected in the direction determination process, with respect to a target pixel from which a defect has been detected in the defect detection process,

wherein the direction determination process is performed using a weighted addition result of a plurality of types of gradient information calculated through a plurality of different gradient detection processes.

2. The image processing apparatus according to claim 1, wherein the image signal correction section calculates pixel value gradient information corresponding to a high frequency texture, pixel value gradient information corresponding to a low frequency texture, and pixel value gradient information corresponding to a luminance signal in the direction determination process, and detects a direction having a minimum pixel value gradient based on a weighted addition result of the three types of gradient information.

3. The image processing apparatus according to claim 2, wherein the image signal correction section calculates the pixel value gradient information corresponding to the high frequency texture using a pixel value difference of adjacent pixels, and calculates the pixel value gradient information corresponding to the low frequency texture using a pixel value difference of non-adjacent pixels.

4. The image processing apparatus according to claim 2, wherein the image signal correction section calculates a luminance signal based on pixel values of RGB pixels in units of pixel areas including the RGB pixels, and calculates the pixel value gradient information corresponding to the luminance signal using the calculated luminance signal in units of areas.

5. The image processing apparatus according to claim 1, wherein the image signal correction section performs a process of changing a weight set in the weighted addition process of the three types of gradient information according to resolution of an output image, sets a weight of the pixel value gradient information corresponding to the high frequency texture to be higher than weights of other types of gradient information when the resolution of the output image is high, and sets a weight of the pixel value gradient information corresponding to the low frequency texture to be higher than weights of other types of gradient information when the resolution of the output image is low.

6. The image processing apparatus according to claim 1, wherein the image signal correction section performs a process of changing a weight set in the weighted addition process of the three types of gradient information according to a frequency band of an input image to be processed, sets a weight of the pixel value gradient information corresponding to the high frequency texture to be higher than weights of other types of gradient information when the input image includes many high frequency regions, and sets a weight of the pixel value gradient information corresponding to the low frequency texture to be higher than weights of other types of gradient information when the input image includes many low frequency regions.

7. The image processing apparatus according to claim 1, wherein the image signal correction section performs pixel value correction of an image in which RGB colors are arranged in 2×

2 units of four pixels, or an image in which RGBW colors are arranged in 2×

2 units of four pixels.

8. The image processing apparatus according to claim 1, wherein, in the defect detection process, the image signal correction section selects a pixel with a color equal to a color of a target pixel, which is to be subject to defect detection, from the minimum gradient direction as a reference pixel, compares a plurality of Laplacians calculated based on different combinations of the target pixel and the selected pixel with a predetermined threshold value, and determines whether the target pixel is a defective pixel based on a result of the comparison.

9. The image processing apparatus according to claim 8, wherein the image signal correction section selects four pixels with a color equal to the color of the target pixel, which is to be subject to the defect detection, from the minimum gradient direction as reference pixels, compares three Laplacians calculated based on different combinations of the target pixel and the two selected pixels with a predetermined threshold value, and determines that the target pixel is a defective pixel when all three of the Laplacians are larger than the threshold value.

10. The image processing apparatus according to claim 8, wherein, in the defect detection process, when only four pixels with a color equal to the color of the target pixel, which is to be subject to the defect detection, are unselectable from the minimum gradient direction in a predetermined reference area, the image signal correction section performs pixel interpolation on a position of a pixel with a color different from the color of the target pixel in the minimum gradient direction based on a pixel value of a pixel with a color equal to the color of the target pixel around the position of the pixel with the different color, and sets an interpolation pixel generated through the pixel interpolation as a reference pixel.

11. The image processing apparatus according to claim 8, wherein, in the defect correction process, the image signal correction section calculates a corrected pixel value of the target pixel through weighted addition of a pixel value of the reference pixel.

12. The image processing apparatus according to claim 8, wherein, in the defect detection process, the image signal correction section calculates a pixel value gradient between two reference pixels at both sides of the target pixel, and calculates a corrected pixel value of the target pixel through weighted addition of pixel values of two pixels in a direction in which the pixel value gradient is small.

13. The image processing apparatus according to claim 1, wherein the image signal correction section performs a highlight error correction determination process of determining whether or not the correction process performed in the defect detection process is highlight error correction, outputs an original pixel value before the correction when it is determined that the correction process is the highlight error correction, and outputs a corrected pixel value when it is determined that the correction process is not the highlight error correction.

14. An image processing method performed by an image processing apparatus, the method comprising performing, with an image signal correction section:

a direction determination process of detecting a direction having a minimum pixel value gradient as a pixel value gradient direction in a pixel area including a target pixel;

a defect detection process of calculating a Laplacian based on a pixel value of a reference pixel in a minimum gradient direction detected in the direction determination process with respect to the target pixel, and determining presence or absence of a defect of the target pixel; and

a defect correction process of performing calculation of a corrected pixel value, which is obtained by applying the pixel value of the reference pixel in the direction detected in the direction determination process, with respect to a target pixel from which a defect has been detected in the defect detection process,

wherein the direction determination process is performed using a weighted addition result of a plurality of types of gradient information calculated through a plurality of different gradient detection processes.

15. A program for causing an image processing apparatus to perform image processing,

wherein the program causes an image signal correction section to perform:

a direction determination process of detecting a direction having a minimum pixel value gradient as a pixel value gradient direction in a pixel area including a target pixel;

a defect detection process of calculating a Laplacian based on a pixel value of a reference pixel in a minimum gradient direction detected in the direction determination process with respect to the target pixel, and determining presence or absence of a defect of the target pixel; and

a defect correction process of performing calculation of a corrected pixel value, which is obtained by applying the pixel value of the reference pixel in the direction detected in the direction determination process, with respect to a target pixel from which a defect has been detected in the defect detection process,

wherein the direction determination process is performed using a weighted addition result of a plurality of types of gradient information calculated through a plurality of different gradient detection processes.