Image denoising device, image denoising method, and image denoising program

An image denoising method comprising:

• a gradient direction detection step of detecting a gradient direction of values of pixels contained in an area consisting of N×N pixels including a target pixel at the center of the area, where N is an odd number no less than 3;
• a selecting step of selecting N pixels as selection pixels from among the N×N pixels in a direction orthogonal to the gradient direction, the selection pixels including the target pixel;
• a filter coefficient initialization step of initializing filter coefficients respectively corresponding to the selection pixels;
• a reference value determination step of determining, for each of the selection pixels, a reference value for correction of the corresponding filter coefficient, based on pixel values of pixels determined by the gradient direction;
• a filter coefficient correction step of correcting, for each of the selection pixels, an initial value of the corresponding filter coefficient, based on the corresponding reference value;
• and
• a pixel value calculation step of calculating an output pixel value of the target pixel, based on pixel values of the selection pixels and corrected values of the filter coefficients.

An image denoising program for causing a computer to perform:

• a gradient direction detection step of detecting a gradient direction of values of pixels contained in an area consisting of N×N pixels including a target pixel at the center of the area, where N is an odd number no less than 3;
• a selecting step of selecting N pixels as selection pixels from among the N×N pixels in a direction orthogonal to the gradient direction, the selection pixels including the target pixel;
• a filter coefficient initialization step of initializing filter coefficients respectively corresponding to the selection pixels;
• a reference value determination step of determining, for each of the selection pixels, a reference value for correction of the corresponding filter coefficient, based on pixel values of pixels determined by the gradient direction;
• a filter coefficient correction step of correcting, for each of the selection pixels, an initial value of the corresponding filter coefficient, based on the corresponding reference value;
• and
• a pixel value calculation step of calculating an output pixel value of the target pixel, based on pixel values of the selection pixels and corrected values of the filter coefficients.