Image processing apparatus, image processing method, and medium storing image processing program

An image processing method executed by an image processing apparatus for quantizing an input image, the method comprising:

• a first image generation step of generating, from the input image, a reflectance image that represents a reflectance distribution, and an illuminance component image that represents an illuminance distribution;
• a region specifying step of specifying a plurality of small regions divided based on illuminance components of the illuminance component image generated in the first image generation step;
• a second image generation step of generating a quantized image from the reflectance image generated in the first image generation step for respective small regions specified in the region specifying step;
• a region acquisition step of acquiring regions having equal quantized pixel values in the quantized image generated in the second image generation step;
• a pixel value acquisition step of acquiring representative pixel values for respective regions corresponding to the regions acquired in the region acquisition step based on the illuminance component image generated in the first image generation step;
• and
• a correction step of correcting quantized pixel values of the respective regions acquired in the region acquisition step using the representative pixel values acquired in the pixel value acquisition step.

A computer-readable medium storing an image processing program for quantizing an input image, the program making a computer function to:

• generate, from the input image, a reflectance image that represents a reflectance distribution, and an illuminance component image that represents an illuminance distribution;
• specify a plurality of small regions divided based on illuminance components of the generated illuminance component image;
• generate a quantized image from the generated reflectance image for respective specified small regions;
• acquire regions having equal quantized pixel values in the generated quantized image;
• acquire representative pixel values for respective acquired regions based on the generated illuminance component image;
• and
• correct quantized pixel values of the respective acquired regions using the acquired representative pixel values.