Patent ID: 7742190

Claim:
An image processing method comprising the steps of: detecting a dynamic range of input image data; performing resolution conversion processing of enlarging or reducing the image data, during which a bit number of grayscale levels of the image data is increased; and performing dithering processing, by selecting one from a plurality of dither matrices respectively having different pseudo-grayscale levels based on a combination of a parameter indicating the dynamic range of the image data and a parameter indicating the type of resolution conversion processing, to reduce the bit number of grayscale levels of the image data whose resolution has been converted in the resolution conversion processing, wherein said performing dithering processing step selects a dither matrix having a relatively large pseudo-grayscale level when the resolution conversion processing is enlargement processing or when the dynamic range of the image data is relatively narrow, the plurality of dither matrices include at least four dither matrices respectively having pseudo-grayscale levels A, B, C, and D (A>B>C>D), said performing dithering processing step selects the dither matrix having pseudo-grayscale level A when the type of the resolution conversion processing is enlargement processing and the dynamic range of the input image data is relatively narrow, said performing dithering processing step selects the dither matrix having pseudo-grayscale level B when the type of the resolution conversion processing is enlargement processing and the dynamic range of the input image data is relatively wide, said performing dithering processing step selects the dither matrix having pseudo-grayscale level C when the type of the resolution conversion processing is reduction processing and the dynamic range of the input image data is relatively narrow, and said performing dithering processing step selects the dither matrix having pseudo-grayscale level D is selected when the type of the resolution conversion processing is reduction processing and the dynamic range of the input image data is relatively wide, and at least some of the steps are performed using a computer.