Image processing apparatus, control method thereof, and storage medium

An image processing apparatus, comprising:

• at least one processor or circuit configured to function as following units:
• an image reduction unit configured to generate one or more reduced images by reducing an input image and generate an image group that includes the input image and the one or more reduced images;
• and
• a gain map generation unit configured to respectively generate a gain map that indicates a gain value at each position in an image by applying a predetermined tone characteristic to each image in the image group, wherein the gain map generation unit generates the gain map by applying, to the image out of the image group for which a resolution is relatively lowest, tone characteristics for which a characteristic differs for each subject region included in the image;
• a gain map composing unit configured to generate a composed gain map by composing a plurality of gain maps generated based on each image of the image group;
• and
• an image conversion unit configured to perform a tone conversion by using the composed gain map on the input image.

A control method of an image processing apparatus, the method comprising:

• generating one or more reduced images that are reduced in a stepwise fashion based on an input image, the input image and the reduced images forming hierarchized images;
• generating a gain map for each hierarchical level that represents a gain at each pixel position of an image, by applying a first tone characteristic to each of the hierarchized images and also further applying a second tone characteristic to at least one of the one or more reduced images;
• and
• composing gain maps generated for each hierarchical level to generate a composed gain map that represents gain applied to each pixel position of the input image,
• wherein, for each subject region, the first tone characteristic and the second tone characteristic are applied to the at least one of the one or more reduced images, and
• wherein the first tone characteristic and the second tone characteristic are mutually different tone characteristics associated with a respective subject region included in the input image.

A control method of an image processing apparatus, the method comprising:

• generating at least one or more reduced images by reducing an input image and generate an image group that includes the input image and the at least one or more reduced images;
• respectively generating a gain map that indicates a gain value at each position in an image by applying a predetermined a tone characteristic to each image in the image group, wherein the gain map is generated by applying, to an image out of the image group for which a resolution is relatively low, tone characteristics for which a characteristic differs for each subject region included in the image;
• generating a composed gain map by composing a plurality of gain maps generated based on each image of the image group;
• and
• performing a tone conversion by using the composed gain map on the input image.

A non-transitory computer-readable storage medium storing a computer program for causing a computer to function as an image processing apparatus comprising:

• an image generation unit configured to generate one or more reduced images that are reduced in a stepwise fashion based on an input image, the input image and the reduced images forming hierarchized images;
• a gain map generation unit configured to generate a gain map for each hierarchical level that represents a gain at each pixel position of an image, by applying a first tone characteristic to each of the hierarchized images and also further applying a second tone characteristic to at least one of the one or more reduced images;
• and
• a composing unit configured to compose gain maps generated for each hierarchical level to generate a composed gain map that represents gain applied to each pixel position of the input image,
• wherein the gain map generation unit applies, for each subject region, the first tone characteristic and the second tone characteristic to the at least one of the one or more reduced images, and
• wherein the first tone characteristic and the second tone characteristic are mutually different tone characteristics associated with a respective subject region included in the input image.