Method and apparatus for forming color images

Claim 2

The method for forming color images according to Claim 1 in which the input color is judged to be unreproducible by the printer if one of color components of said first color density signal has a density out of a range defined by the minimum color density equal to that of a print sheet used for printing and the maximum color density reproducible by the printer.

Claim 3

The method for forming color images according to Claim 1 in which said second color correction process is comprised of color reproduction prediction process for predicting colors reproducible by the printer with respect to said target color, calculation process for calculating evaluation values using at least one evaluation function for evaluating a chromatic relation between each of predicted colors and said target color and search process for seeking for the best evaluation value among said evaluation values obtained in said calculation process to obtain said second color density signal based on the predicted color giving said best evaluation value.

Claim 4

The method for forming color image according to Claim 3 in which the color density signal to be converted is the first color density signal and said prediction process is performed by inverse operation of the first color density signal to a color signal in the color space of said input color signal.

Claim 5

The method for forming color images according to Claim 3 wherein a plurality of evaluation functions are provided and used selectively in accordance with color components of said input color signal.

Claim 6

The method for forming color images according to claim 5 wherein each of said plurality of evaluation functions E(i)[i = 1, ..., n: n = the total number of the evaluation functions] is given by the following equation; E(i) = {(a i ΔL(i)² + b i ΔH uv (i)² + c i ΔS uv (i)²) / (a(i) + b(i) + c(i))} 1/2 wherein a(i), b(i), c(i): weighing coefficients ΔL(i) = L₀* - L(i)* ΔS uv = S₀ - S(i) S₀ = (u₀*² + v₀*²) 1/2 S(i) = (u(i)*² + v(i)*²) 1/2 ΔH uv = (S(i) + S₀) · |ϑ₀ - ϑ(i)|/2 ϑ₀ = tan⁻¹(v₀*/u₀*) ϑ(i) = tan⁻¹(v(i)*/u(i)*) L₀*, u₀*, v₀* coordinates of the target color in L*, u*, v* space; L(i)*, u(i)*, v(i)* coordinates of the color to be reproduced.

Claim 7

The method for forming color images according to Claim 1 wherein a plurality of neighborhood color density signals are calculated from input color signals near to a considered input color signal and the color density signal corresponding to the considered input color signal is corrected by a neighborhood calculation using said plurality of neighborhood color density signals whereby the color density of the printer is controlled by the color density signal corrected by said neighborhood calculation.

Claim 8

A color image forming apparatus for controlling a color printer which comprises a first correction means for performing a first color correction to an input color signal using upper bits of said input color signal to obtain a representative point of said input color signal and for converting said representative point of said input color signal into a first color density signal, a judgment means for judging whether or not said representative point of said input color signal is a color reproducible by a printer, a second color correction means for performing a second color correction to said representative point of said input color signal when judged by said judgment means that said representative point of said input color signal is not a color reproducible by the printer, said second color correction converting said representative point of said input color signal into a second color density signal which will reproduce a color visually nearest to said representative point of said input color signal within the color gamut reproducible by the printer, a memory means for storing said first and second color density signals, a memory control means for addressing said memory means using upper bit information of said input color signal and reading the stored color density signal from said memory means, and an interpolation means for performing an interpolation operation to said stored color density signal read from said memory means using lower bit information of said input color information to obtain a final color density signal in response to which the color printer performs color printing operation.