JP2892677B

PURPOSE:To allow the contrast and brightness of an area being an observation object to coincide with a reference image, while suppressing an artifact of a processing image by executing a density conversion by using an image after eliminating a background. CONSTITUTION:From an input image 10, a background eliminated input image 11 formed by eliminating a background part in an image is derived, and from its object area, an input histogram 12 is calculated. On the other hand, from an image of the same kind as the input image, that is, an image whose photographing device, part, etc., coincide and an image emphasized for diagnosis, that is, a reference image 13, a background eliminated image 14 is derived, and also, a reference histogram 15 is calculated. Subsequently, such a density conversion function 16 as the input histogram coincides with the reference histogram is derived, and the density conversion is executed to all picture element of the input image by using this conversion function 16. In such a way, the density conversion using a density distribution of only the object area can be executed, an appropriate density conversion processing is realized, and the input image 10 can be allowed to coincide with contrast and brightness of the reference image 13 without generating an artifact.