US Patent 7837285 Inkjet printing using protective ink

A method for modifying an input digital image having one or more color channels corresponding to one or more color inks and a protective ink channel corresponding to a substantially clear protective ink, each channel having an (x,y) array of pixel values, to form a modified digital image including computing a first value responsive to corresponding pixel values of the one or more color channels; computing a second value responsive to the corresponding pixel value of the protective ink channel; and modifying the corresponding pixel value of the protective ink channel responsive to the first and second values.