COLOR PREDICTION METHOD, PRINT DATA GENERATION APPARATUS, AND COLOR PREDICTION PROGRAM
FIG2 is a diagram showing an overall configuration of a printing system for achieving a color prediction method according to an embodiment of the present invention
FIG2 is a diagram showing an overall configuration of a printing system for achieving a color prediction method according to one embodiment of the present invention. The printing system includes: a print data generation apparatus 100 that generates print data by performing various processes on submitted data such as a PDF file; a plate making apparatus 200 that produces a printing plate on the basis of the print data; a printing apparatus 300 that performs printing using the printing plate produced by the plate making apparatus 200; a digital printing apparatus 400 such as an inkjet printer/copier that performs printing on the basis of the print data which is digital data without using the printing plate; and a colorimeter 500 for measuring a color. The print data generation apparatus 100, the plate making apparatus 200, the digital printing apparatus 400, and the colorimeter 500 are communicably interconnected by a communication line 600. Note that the colorimeter 500 used in the present embodiment is assumed to be a spectral colorimeter.
diagram
100
400
digital printing apparatus
600
communication line
300
printing apparatus
500
colorimeter
200
plate making apparatus
['8. A print data generation apparatus (100) that generates print data in a format printable by a digital printing apparatus (400) on the basis of submitted data, the print data generation apparatus (100) comprising: color prediction means (S610 to S630) configured to perform a color prediction process in which pixel data is read from the submitted data on a pixel-by-pixel basis, and a color of the read pixel data is predicted; XYZ data generation means (S640) configured to generate XYZ data representing color tristimulus values X, Y, and Z on the basis of a result obtained by the color prediction process; first data conversion means (S650) configured to convert the XYZ data into Lab data that is data of a CIELAB color space; and second data conversion means (S660) configured to convert the Lab data into print data in a format printable  by the digital printing apparatus, wherein the color prediction process includes a process for predicting a color obtained by sequentially overprinting, on a base material, inks of a first printing color to an Nth (N is an integer of 2 or more) printing color, the color prediction means (S610 to S630) includes first reflectance obtaining means (S10) configured to obtain, as a first reflectance, a reflectance of a unit region with a state where an ink of the first printing color is applied on the base material, and calculation means (S20) configured to perform a calculation process which is executed (N-1) times for pixel data of one pixel, and in the calculation process, during a Kth (K is an integer of 1 or more and N-1 or less) execution, a reflectance of the unit region with a state where inks of the first printing color to a (K+1)th printing color are sequentially overprinted on the base material is calculated, and the calculation means (S30) includes second reflectance calculation means (S310) configured to calculate, as a second reflectance, a reflectance of a printing region with a state where the ink of the first printing color is applied on the base material, when a value of the K is 1, and to calculate, as a second  reflectance, a reflectance of a printing region with a state where an ink of a Kth printing color is overprinted on an ink of a (K-1)th printing color, when the value of the K is 2 or more, third reflectance calculation means (S320 and S330) configured to calculate, as a third reflectance, a reflectance of the unit region with a state where, assuming that a transparent ink is applied on the base material, an ink of a (K+1)th printing color is overprinted on the transparent ink, first conversion equation calculation means (S340) configured to obtain a first conversion equation representing a line connecting first coordinates and second coordinates regarding a color prediction coordinate system where an abscissa represents a product of a reflectance of a background and a reflectance of a foreground and an ordinate represents a reflectance of a state where the background and the foreground overlap, the first coordinates corresponding to a combination of a product of a fourth reflectance that is a reflectance of the base material and a fifth reflectance that is a reflectance of a state where the ink of the (K+1)th printing color is applied on the base material, and the third reflectance, the second coordinates corresponding to a combination of a product of a sixth reflectance that is a reflectance of a  state where a black ink is applied on the base material and the fifth reflectance, and a seventh reflectance that is a reflectance of a state where the ink of the (K+1)th printing color is overprinted on the black ink, eighth reflectance calculation means (S350) configured to calculate, as an eighth reflectance, a reflectance of a printing region with a state where the ink of the (K+1)th printing color is overprinted on the ink of the Kth printing color on the basis of the second reflectance and the fifth reflectance, using the first conversion equation, second conversion equation calculation means (S360) configured to obtain a second conversion equation representing a line connecting third coordinates and fourth coordinates regarding the color prediction coordinate system, the third coordinates corresponding to a combination of a product of the second reflectance and the fifth reflectance, and the eighth reflectance, the fourth coordinates corresponding to a combination of a product of the fourth reflectance and the fifth reflectance, and the fifth reflectance, and first reflectance update means (S370) configured to calculate a reflectance of the unit region with a state where the inks of the first printing color to the (K+1)th printing color are sequentially overprinted on the base  material on the basis of the first reflectance and the fifth reflectance, using the second conversion equation, and to update the first reflectance with the calculated reflectance.']