Image processing apparatus, method and storage medium for reducing color noise and false color

An image processing method comprising:

• reducing color noise of an input image to generate a noise-reduced image;
• performing a first generation to generate a color difference signal from the noise-reduced image;
• generating hierarchical images including at least two or more reduced images from the noise-reduced image;
• performing a second generation to generate coloring-suppressed color difference signals from the reduced images;
• and
• combining the color difference signal generated in the first generation and each of the color difference signals generated in the second generation, wherein
• in the second generation, for each pixel in a reduced image in the hierarchy, iteratively through the hierarchical images, selects as its color difference signal one of the color difference signals of said reduced image and of another reduced image expanded to the resolution of said reduced image, at the same location as said pixel, based on a magnitude that is a function of the respective color difference signals, to generate the coloring-suppressed color difference signals, and
• wherein said another reduced image is adjacent to said reduced image in the hierarchy and of a lower resolution.

A non-transitory computer-readable storage medium storing a computer program that causes a computer to function as:

• a noise reduction unit configured to reduce color noise of an input image to generate a noise-reduced image;
• a first generation unit configured to generate a color difference signal from the noise-reduced image;
• a reduction processing unit configured to generate hierarchical images including at least two or more reduced images from the noise-reduced image;
• a second generation unit that generates coloring-suppressed color difference signals from the reduced images;
• and
• a combining unit configured to combine the color difference signal generated by the first generation unit with each of the color difference signals generated by the second generation unit, wherein
• for each pixel in a reduced image in the hierarchy, the second generation unit, iteratively through the hierarchical images, selects as its color difference signal one of the color difference signals of said reduced image and of another reduced image expanded to the resolution of said reduced image, at the same location as said pixel, based on a magnitude that is a function of the respective color difference signals, to generate the coloring-suppressed color difference signals, and
• wherein said another reduced image is adjacent to said reduced image in the hierarchy and of a lower resolution.