A method of processing an image in a diagnostic apparatus of diagnosing a disease using a captured image of an affected area, comprising: a memorizing step of memorizing the captured image, and a processing step of processing the captured image memorized, wherein in the processing step a region to be diagnosed is subjected to a highlighting process with a specified color thereof maintained; characterised in that the processing step comprises: a first separating step of separating the captured image into a brightness component and a color information component; and a second separation step of separating the brightness component into a base component and a detail component, wherein due to the highlighting step: the base component is attenuated in accordance with the formula: B'=(B-C1)*K1+C1, wherein B' is a base component after attenuation, B is a base component before attenuation, C1 is a center location of compression, and K1 is a compression ratio; and the detail component is highlighted in accordance with the formula: D'=D*K2, wherein D' is a detail component after highlighting, D is a detail component before highlighting, and K2 is a highlighting ratio. a memorizing step of memorizing the captured image, and a processing step of processing the captured image memorized, wherein in the processing step a region to be diagnosed is subjected to a highlighting process with a specified color thereof maintained; characterised in that the processing step comprises: a first separating step of separating the captured image into a brightness component and a color information component; and a second separation step of separating the brightness component into a base component and a detail component, wherein due to the highlighting step: the base component is attenuated in accordance with the formula: B'=(B-C1)*K1+C1, wherein B' is a base component after attenuation, B is a base component before attenuation, C1 is a center location of compression, and K1 is a compression ratio; and the detail component is highlighted in accordance with the formula: D'=D*K2, wherein D' is a detail component after highlighting, D is a detail component before highlighting, and K2 is a highlighting ratio. a first separating step of separating the captured image into a brightness component and a color information component; and a second separation step of separating the brightness component into a base component and a detail component, wherein due to the highlighting step: the base component is attenuated in accordance with the formula: B'=(B-C1)*K1+C1, wherein B' is a base component after attenuation, B is a base component before attenuation, C1 is a center location of compression, and K1 is a compression ratio; and the detail component is highlighted in accordance with the formula: D'=D*K2, wherein D' is a detail component after highlighting, D is a detail component before highlighting, and K2 is a highlighting ratio. the base component is attenuated in accordance with the formula: B'=(B-C1)*K1+C1, wherein B' is a base component after attenuation, B is a base component before attenuation, C1 is a center location of compression, and K1 is a compression ratio; and the detail component is highlighted in accordance with the formula: D'=D*K2, wherein D' is a detail component after highlighting, D is a detail component before highlighting, and K2 is a highlighting ratio.