In order to produce accurate color on a color printer, it is necessary to calibrate the printer. In essense, this involves printing a chart of known colors, then measuring the actual colors produced by the printer. The transformation from desired colors to actual colors can then be inverted to produce a transformation which can be used to compute the input colors which, when printed, will produce the desired output.
A further problem is that it is not physically possible to print all possible colors. For example, it might not be possible to exactly reproduce a bright shade of blue on a particular printer. Such colors are called "out-of-gamut" and it is necessary to handle them by mapping them into colors which can be produced by the printer. Algorithms for this mapping have been a subject of research.
Our group has received much assistance from the printer group at the IBM Almaden Research Laboratory in our printer efforts.
Recently we have also contributed halftoning algorithms to improve black and white printer outputs for the IBM Printer division. Some of this work is described in a 1997 IBM Research magazine article. Another talks about work done on descreening of halftone images in a 2000 IBM Research magazine article.
Here is a sample image that demonstrates descreening.
