Color correcting circuit for thermal printer selectively outputting a second degree correction operation result and a modified result thereof

Claim 1

A color correcting circuit for a thermal printer for carrying out a predetermined color correction operation with respect to input signals of three additive primary colors related to an input image, the thermal printer printing an output image based on the predetermined color correction operation which is dependent on correction data by use of color inks of three subtractive primary colors, said color correcting circuit compensating for a difference in a characteristic of a color separation system from which the input signals are obtained and a characteristic of a color mixing system of the thermal printer so as to obtain an output image in which color reproduction is approximately the same as that in the input image, said color correcting circuit comprising: first means for carrying out a first degree correction operation on the input signals for each additive primary color so that a ratio between a density of the input image and a density of the output image becomes linear, said first means outputting a first degree correction operation result which is an operation result of the first degree correction operation; second means for carrying out a second degree correction operation on the input signals for each additive primary color by use of the method of least squares so that a difference between the density of the input image and the density of the output image is reduced when compared with the difference in the case where the second degree correction operation is not carried out, said second means outputting a second degree correction operation result which is an operation result of the second degree correction operation; and difference limiting means responsive to the first degree correction operation result and the second degree correction operation result for selectively outputting as the correction data the second degree correction operation result then a difference between the second degree correction operation result and the first degree correction operation result falls within a predetermined range about the first degree correction operation result, and for selectively outputting as the correction data a value which is deviated from the first degree correction operation result by a boundary value of said predetermined range when the difference between the second degree correction operation result and the first degree correction operation result falls outside said predetermined range, said color correcting circuit outputting output signals of the three subtractive primary colors describing the output image by carrying out the predetermined color correction operation based on the correction data outputted from said difference limiting means.