Modified Neugebauer model for halftone imaging systems
View Patent ↗A technique for profiling a color printing device employs a modified Neugebauer color mixing model. The modeling technique makes use of a variable dot gain value and “n factor.” The variable dot gain adjustment value may vary according to the particular tristimulus channel under evaluation. In addition, the variable dot gain value may vary according to the particular Neugebauer primary over which a halftone dot is printed. Accordingly, the technique may rely on an array of different dot gain values and n factors that correspond to different combinations of color channels and overprint conditions. As a further feature, the techniques may rely on a dot gain formula that relates halftone dot variation, i.e., fringe thickness, to the size of the halftone dot. This relationship tends to produce a dot gain model that more closely resembles the actual dot gain behavior on a printing press.
1. A method for transforming image data values associated with a halftone imaging device, the method comprising:
defining a mathematical model based on Neugebauer equations that converts dot size input values for a plurality of printing inks to tristimulus values;
defining a dot gain function that converts input dot sizes into adjusted output dot sizes based on a value of a dot gain parameter wherein the dot gain function is characterized by a dot gain parameter value representing a maximum gain for an intermediate input dot size and no gain for minimum and maximum input dot sizes;
adjusting dot size values for each dot size input value used in said Neugebauer calculations by means of said dot gain function and said dot gain parameter;
determining a single dot gain parameter value, for use in the dot gain function, for each single-colorant Neugebauer primary that characterizes the relationship of dot size input values to measured tristimulus values for each single colorant ink;
determining a unique correction value for a dot gain parameter for each single colorant Neugebauer primary associated with printing that single colorant Neugebauer primary on each of the remaining Neugebauer primaries that do not contain said single colorant Neugebauer primary;
calculating tristimulus color values as a function of the dot sizes of said plurality of printing inks and the dot gain function to characterize a color response of the halftone imaging device;
generating a profile based on the color response of the halftone imaging device;
performing one or more of the following steps:
adapting color values for use with the halftone imaging device based on the profile;
printing the adapted color values on the halftone imaging device; and
preparing color values for a different device based on the profile wherein the color values are converted from color values intended for the halftone imaging device.
2. The method of claim 1 , wherein generating the profile includes generating a mapping of device-dependent coordinates to device-independent coordinates.
3. The method of claim 2 , further comprising generating a link between the halftone color imaging device and another imaging device based at least in part on the profile.
4. The method of claim 1 , wherein determining the tristimulus color values includes determining XYZ tristimulus color values.
5. The method of claim 1 , wherein determining the tristimulus color channel values includes determining L*a*b* tristimulus color values.
6. The method of claim 1 , wherein determining the dot gain values includes determining the dot gain values as a function of the size of a halftone dot.
7. The method of claim 1 , wherein the colorant channels include cyan, magenta and yellow.
8. The method of claim 1 wherein converting image data with said profile for output on a display system or printing system.