Image processing apparatus, image processing method, and storage medium

An image processing method comprising:

• generating, from an input image, a plurality of hierarchical images having different frequency bands;
• calculating, for each of the hierarchical images, a gain based on a luminance value for each image area by using a tone conversion curve that is set according to the corresponding frequency band, wherein the tone conversion curve assigns tone with priority to different luminance ranges according to the frequency bands of the hierarchical images;
• determining a combined gain by combining gains that are set for the plurality of hierarchical images;
• performing tone conversion on the input image by using the combined gain determined by the determining;
• and
• generating, based on the input image, a plurality of tone conversion curves including a first tone conversion curve and a second tone conversion curve that assigns tone with priority to a different luminance range from the first tone conversion curve, and generate a tone conversion curve for each of the plurality of hierarchical images by weighting and adding the plurality of tone conversion curves, wherein the adding is performed by varying weights of the first tone conversion curve and the second tone conversion curve according to the frequency bands of the hierarchical images.

A storage medium storing a program for causing a computer to execute steps of an image processing method, the image processing method comprising:

• generating, from an input image, a plurality of hierarchical images having different frequency bands;
• calculating, for each of the hierarchical images, a gain based on a luminance value for each image area by using a tone conversion curve that is set according to the corresponding frequency band, wherein the tone conversion curve assigns tone with priority to different luminance ranges according to the frequency bands of the hierarchical images;
• determining a combined gain by combining gains that are set for the plurality of hierarchical images;
• performing tone conversion on the input image by using the combined gain determined by the determining;
• and
• generating, based on the input image, a plurality of tone conversion curves including a first tone conversion curve and a second tone conversion curve that assigns tone with priority to a different luminance range from the first tone conversion curve, and generate a tone conversion curve for each of the plurality of hierarchical images by weighting and adding the plurality of tone conversion curves, wherein the adding is performed by varying weights of the first tone conversion curve and the second tone conversion curve according to the frequency bands of the hierarchical images.