Patent ID: 7433515

Claim:
An image processing apparatus for performing gradation conversion processing for an object image, said apparatus comprising: determination means for determining variables for specifying a gradation conversion function, from a relationship between the variables and a processed image obtained by performing gradation conversion processing for the object image with the gradation conversion function; gradation conversion means for performing gradation conversion processing for the object image with the gradation conversion function specified by the variables determined by said determination means; histogram forming means for forming a histogram of the processed image obtained by performing the gradation conversion processing of the object image with the gradation conversion function specified by the variables; index calculation means for calculating an index from the histogram obtained by said histogram forming means and an average number of pixels of the object image; and analysis means for analyzing a relationship between the index obtained by said index calculation means and the variables, and determining the variables for specifying the gradation conversion function for performing gradation conversion of the object image from a result of the analysis.