Patent ID: 8131518

Claim:
A method for forming a transmission type spectral filter having a multilayer film on a transparent base material, the method comprising the steps of: describing a spectral transmittance T(λ) of the multilayer film as T(λ)=T(p 1 , p 2 , . . . , p n ) by using parameters p 1 , p 2 , . . . , and p n composed of divided wavelength intervals and transmittances corresponding to the respective wavelength intervals, or function parameters p 1 , p 2 , . . . , and p n when transmittances at a given wavelength are represented as a function model; optimizing the parameters p 1 , p 2 , . . . and p n such that a sensitivity difference pattern formed from sensitivity differences in a sensitivity wavelength band of a light receiving member via the multilayer film between combined two colors for arbitrary combinations that two colors in an object color group consisting of a plurality of specified colors are combined, is made into a desired sensitivity difference pattern; and forming the transmission type spectral filter on the basis of an optimum T(λ) described by using the optimized parameters p 1 , p 2 , . . . , and p n ; and wherein the optimum T(λ) is set such that, in specific combinations among the respective combinations, a color difference via the spectral filter is less than a color difference without the spectral filter, and in the other specific combinations, a color difference via the spectral filter is greater than a color difference without the spectral filter.