Stochastic Printing Process Renders Larger CMYK Gamut

Stochastic Printing Process Renders Larger CMYK Gamut

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Stochastic Printing Process Renders Larger CMYK Gamut
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Stochastic printing process ability to produce a larger CMYK color gamut is one of the best secrets to producing high quality color on press.

Conventional halftones, often referred to as AM screens (amplitude modulated), distribute ink over a grid of dots that increase in size for darker tones. Throughout the tone scale, the frequency of dots remains the same, but the size or amplitude increases. The ink and water requirements vary greatly throughout the tonal range, causing a basic lithographic instability for which there are no on press controls.

An alternative to traditional halftone printing is stochastic printing process. The ink water requirements are more evenly distributed throughout the tonal range thereby overcoming the inherent instability of the AM screen. Stochastic printing is referred to as FM screening (frequency modulated), because the number and frequency of dots changes with tonality. Note that the average size of dot structures remains relatively constant through the tone scale. The dots are positioned in a pseudo random pattern to avoid moiré and patterning problems.

Many people are aware that stochastic printing (FM) brings certain quality benefits to print, but few have realized the true potential of stochastic printing to deliver more predictable and stable color to their presswork and a larger CMYK color gamut.

Let’s look at the comparison of primary colors (Red, Green, Blue) and how the screens compare in trapping/overprinting subtractive colors (Cyan, Magenta, Yellow).

Stochastic Printing vs Conventional Printing Halftone Dots

Primary Red

Solid Yellow ink trapping/overprinting Magenta tonal range
Observe how much finer stochastic printing process (bottom) appears over conventional printing (top)

 

Primary Green

Solid Yellow ink trapping/overprinting Cyan tonal range
Observe how much finer stochastic printing process (bottom) appears over conventional printing (top) 

 

Primary Blue

Magenta tonal range trapping/overprinting solid Cyan ink
Observe how much finer stochastic printing process (bottom) appears over conventional printing (top)

 

NOTE: the ink sequence on a printing press is black, cyan, magenta and yellow. Each ink gradually decreases in tack for overprinting efficiency to allow primary colors – red, green, blue – to be as bright as possible.

Notice the greater range of tones in all three primary colors with stochastic printing (FM) resulting in a larger CMYK color gamut.

This demonstration shows that stochastic printing (FM) prints cleaner, with greater vibrancy and a midtone color gamut that is not achievable with AM screens.

In the example above, you can see the effect in a number of areas. If you look in the Magenta patches you will see a distinct difference between the AM and stochastic printing (FM).

The tiny dots that make up a stochastic printing (FM) are actually more efficient at trapping and remitting light than AM screens. A small amount of light on the edge of every dot gets scattered through the paper and through the ink. This is what is called optical gain.

With stochastic printing process, a larger percentage of light that hits the printed sheet passes through the ink. This means that less ink is required for a given visual tone and the increased optical effect filters out a greater percentage of the complementary colors that are reflected from the paper surface. It is the complementary colors that contaminate the color we should be seeing and there is less of it getting through with stochastic printing.

True High Definition Color.

Which color would you prefer? Please leave your comments below…

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    8 Comments

  1. how can i separate colors by stockhastic dot in photoshop in screen printing

  2. Rick
    I print on metal substrate using two color presses would it be possible to change from conventional screening to FM screening using these presses

  3. Amazing post!
    How I make this Staccato in Photoshop for digital stuff (not for printing) ?

    • You can simulate an FM screen in photoshop by converting a grayscale image to bitmap and use the ‘diffusion dither’ option. This process will convert an 8-bit grayscale image to a 1-bit bitmap image. The 256 levels of gray will be simulated by a ‘dither’ pattern that will resemble an FM screen – very close. The important step is to make sure you render the bitmap to at a resolution evenly divisible of your output device’s resolution. Example: render the bitmap at resolution of 600 pixels per inch (ppi) for an output device of 2400 dots per inch (dpi) – evenly divisible by a factor of four.

      Very cool technique to try…

  4. I would like to know the how to measure / analyze the staccato screen. (SPARK) we already have analyzer / screen measuring scale for AM screen.

    This scale is to measure the LPI of AM screen.

    But now, we are printing staccato screening also, but i don’t have any analyzer / measuring scale to measure the micron of staccato.
    (we print books with different micro (20/25/36)).
    Thanks… and expecting your BIG help.

    • Hi Daniel,

      There is no true way to measure the frequency, in LPI (lines per inch) of stochastic/staccato screens because of the nature of the pseudo-random screening characteristic of stochastic/staccato. Conventional screening is fixed on a grid and the screen analyzer interferes with the grid pattern causing a moire pattern that ‘points’ to the appropriate screen frequency.

      This is not possible with a dithered, or stochastic, screen.

      The industry buzz is that a 20 micron second order stochastic ‘spot’ will render to approximately 480 lines per inch (lpi). 10 micron spot size will be approximately 600 lines per inch (lpi).

      Does this clear things up for you?

      Rick

      • I have seen copies of various print from printing companies and they will use the FM dot for their commercial type work , but then use an AM dot for their in house things such as a simple newspaper. Is there any particular reason for this that you know of? And/or is it ok to use the FM on newspaper applications as well? the reason i ask is because i have seen papers such as the USA Today newspaper and other newspapers still using the AM or a similar dot anyway…Thanks in advance..

        • It depends on the application.

          If it is a simple newsletter, they, most likely, are printing a smaller publication on a small press and do not have that press/ink combination profiled and neither would they want to go through the expense of doing that.

          Yes, FM screens can be used for newspapers, such as USA Today, however they would require a larger spot size such as 40-50 microns. The larger the spot size, the lower the apparent resolution.

          Unfortunately I rarely see the paper – go figure I’m a printer – but I have seen my local paper printing with what looks like a 200 line screen. This is possible with building accurate plate curves.

          It takes some work, but it looks great in the long run and we need to make printing more like art moving forward….

          Thanks for the note Phillip.

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