The Good, The Bad and the 4 Uglys of Stochastic Screening
By Howie Fenton
Since its introduction nearly two years ago, stochastic screening has received a lot of interest. But what is stochastic screening and what are the advantages and disadvantages of this technology?
"Stochastic" is derived from a Greek work meaning to predict and has been used in mathematics to analyze and predict the movement of particles through a liquid. One way to think about stochastic is as a way of utilizing aspects of screening technology from both flat tints as well as halftones. Flat tints use fixed dot sizes and fixed dot spacing. In contrast screened halftones use variable dot sizes with fixed dot spacing determined by the line screen. Stochastic technology use fixed dot sizing with variable dot spacing.
Imagine a graph measuring the radio wave patterns known as AM and FM. The AM waves represent the older PostScript screening technologies such as Rational tangent (RT) and Supercell (HQS, ABS), while FM stands for frequency modulation which is another term for stochastic.
The height of the wave represents the dot size, so that the higher the wave the greater the dot size. The distance between the wave peaks represents the dot spacing. The AM waves are different in height but equally spaced, giving you variable dot sizes that are unequally spaced. The FM waves are equally high but spaced differently with resulting equal size dots that are variable spaced (it helps to draw it).
The Good News
There are a number of benefits of FM technology. Since stochastic screening does not employ screen angles, moires due to the interfaces of patterns from screening are eliminated. Particularly, subject moires, which occur most frequently in certain images such as woodwork and fabrics. Many versions of stochastic use very small dots which result in greater detail rendition which results in enhanced image quality.
Not using screen angles also reduces the need for the precise press registration. Since frequency modulated screening does not use lines screens it will make 5,6,7 or more color printing more accessible.
Make-ready times, or the time needed to get a press up to speed and ready to produce accurate color, can be reduced because stochastic screening is faster to register and provides more consistent color on press.
In addition, FM technology can utilize scans with lower resolution. Using lower resolution scans can reduce the amount of time spent in manipulated the image, time to send it over a network or RIPed to an imagesetter.
However certain images may require higher input resolutions due to the specific image detail or customer requirements. For jobs that require very high quality, increasing the scan resolution resulting in significantly improved quality.
The Bad News
Stochastic screening is unforgiving. Conventional screening is more tolerant of press deviations and any changes in film and chemical processing are not noticeable in the final result.
FM technology amplifies dot gain. Print production professionals are currently geared for 18 percent dot gain. Films created with stochastic screening will produce 25-35 percent on standard coated stock.
Proofing is one area that requires special attention The cleanliness of the proofing environment is critical because small tiny dust particles or cigarette smoke can cause a pattern on the proof.
Only a few proofing systems can proof stochastic films. The early users report that photographic proofing systems have performed better than Diazo-based systems.
The 4 Uglys
If your considering stochastic screening here a few final points to consider.
While aggressive marketers will say that if you wait for the demand you'll too late, you have to create the demand. For example, Tim Poole, Vice President of Dome Printing in Sacramento was an early adopter of Linotype-Hell's stochastic screening and found that none of the agencies or design firms in his area were asking for it. Poole created the demand.
Poole says, "We produced three jobs: a flyer for the Northern California Chapter of the PIA, a poster for a local charity, and a self-promotional piece that used both stochastic screening and HiFi color. Then we held an open house to show off the new technology, and discuss how best to use it. We had about 600 attendees, and there was tremendous excitement. In the future, Im sure our customers will be asking for it and it will become a standard."