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Why Color Looks so Good – FM Screens Explained

FM, AM, XM, Hybrid, Staccatto, Segundo, stochastic, conventional, 200 lpi, 175 lpi, 20 micron, 10 micron, first order, second order…What does this all mean?

NOTE: Screening is the process after rasterizing PDF files in the RIP (raster image processor) during prepress. Halftone screening is done through software and creates very small dots, or cells, that are imaged onto a printing plate. The tiny dots create the illusion of continuous tone photographs when printed on press.

FM Screening comparison to AM screening - stochastic versus conventional screening
Top: 200 lpi conventional (AM) halftone screen magnified 200x.
Bottom: 20 micron (FM) stochastic screen magnified 200x.
Image: Gordon Pritchard

Advantages to printing with FM screening versus AM screening:

  • Continuous tone photograph reproduction
  • Produces a larger CMYK color gamut on press
  • Renders greater detail
  • Eliminates moire patterns
  • Reduces ink consumption by as much as 10% – notice the ‘pooling’ of ink in conventional dot
  • Produces smoother gradients
  • More consistency in color throughout pressrun
  • Faster ink drying

Conventional screening (150 lpi, 175 lpi, 200 lpi) refers to AM screens, or amplitude modulation. This refers to halftone dots that are fixed on a grid, angled in 30 degree increments (except yellow: 15 degrees) and grow in size based on tonal value.

LPI = lines per inch

Stochastic screening (Staccato) refers to FM screens, or frequency modulation. This refers to micro-dots (20 micron, 10 micron) that are FIXED in size and tone values increase by adding more dots. The dots are rendered in a psuedo-random algorithm making them ideal for high definition details in photography and artwork. The micro-dots are rendered in a ‘weave’ to create very smooth tonal transitions.

Micron =1/1,000,000 of a meter

It’s important to note that FM screens produce a larger CMYK color gamut than AM screens. This occurs because light reflecting off the paper is filtered more efficiently, resulting in less ‘whiteness’ from the paper reflecting into the eye.

Also, reprints are less likely because of the stability in controlling color on press. FM screens are much less likely to be impacted by ink density variations on press. The ink film on press is much thinner and less likely to be affected. Notice in the enlargement photo above the ‘pooling’ of ink in the conventional halftone dots. This causes the press to use more ink than is necessary.

HiDefColor.com utilizes 20 micron Staccato screening for all color printing.

Have you ever seen printing with FM/stochastic screening? Please leave your comments below…

 

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Number One Reason for Reprinting a Print Order

According to a recent survey from GATF (Graphics Arts Technical Foundation), the number one reason for printers’ reprints was due to unacceptable color in print. There has been a general lack of communication, and knowledge, in the print industry that’s been the main cause. Surprisingly, there are many printers that do not have color profiles for their printing conditions. These printers should be avoided due to the lack of being able to produce consistent color off their press.