To provide an image processing method and an image display device capable of displaying a multi-level monochromatic image as an image which hardly causes color irregularity and is suitable for diagnosis by the use of a color display means, and to provide a program used for executing the image display device.

The image processing method comprises: a data input process of inputting monochromatic image data of one channel of n+m bits ((n) is a positive integer of eight or more, (m) is a positive integer of two or more); and a data processing process of producing a color display data group of three channels or more of (n) bits based on the inputted monochromatic image data, wherein a chromaticity difference xyi,i+1 on CIE chromaticity coordinate of display colors corresponding to two input signal values adjacent to each other of the monochromatic image data among display colors of an image displayed on a liquid crystal panel 2 by the color display image data group produced corresponding to the input signal values of the monochromatic image data on the data processing process is a value predetermined in the whole input signal values of the monochromatic image data or less.