Hal Hinderliter

FM screens & Color Management
December 10, 2007

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Question: Our shop currently prints with halftone dots (AM screening) but would like to investigate using FM screening (stochastic). Do I need to recreate our color management profiles, or can I just adjust our RIP curves for the difference in dot gain?

For one expert’s view on this topic, we turn to Ken Elsman, senior color scientist for Global Graphics:

Your question indicates that your current halftone dot (AM) workflow has been color managed for a specific combination of press, ink, paper, and screening, such as a Euclidian dot pattern. Such color management can help assure the widest possible color gamut and promote color accurate printing. However, you’ve probably discovered that if an AM printed job is rerun using FM screens, the dot gain (also known as tone value increase, or TVI) will be different. This is true even if the LPI of your traditional AM screens and the resolution of your FM screens are similar, and is primarily due to differences in ink film thickness and dot patterns/clustering.

Different queues, different profiles
If your desire is to create independent workflows for each choice of screening (i.e., the screening choice is known before each job is printed, and separate RIP queues have been established for each variation of AM or FM screens) then it makes the most sense to go through the same process of press testing and profiling you once performed for your AM work (in other words, create additional color management profiles for FM). 

One queue, then a dot gain adjustment
Alternatively, if the screening determination is not made up front and the work is typically prepared for traditional screening but may be printed FM, a conversion process can be used. Print the project with FM screens, but include a set of tone curves so that you can judge what adjustments may be needed for differences in TVI (dot gain). Once the tone curve values are made to print similar to the values produced by AM screening, then the press sheets will look very close and in some applications may be acceptable color-wise, as this will likely achieve 85-90% of the conversion.

Profiling for the highlights
However, as noted in the first paragraph, differences in the ink film thickness of FM printing along with the randomized pattern of stochastic dots will result in color reproduction differences, most noticeably in highlight areas. These changes can be quantified in the form of a color management profile by profiling the press for FM screens after the TVI curves are applied.

Applying this profile requires an additional prepress step, but will show off the advantages of FM screening through improved visual detail and clean, crisp colors.      

Posted by Hal Hinderliter on December 10, 2007 | Comments (0)