Ed #3 Stochastic / Conventional

Small Things Considered

Small dots are both a blessing and a curse. Stochastic screens can bring out all of the details in the image, including those that may not always be wanted. Sometimes, for example, you can see the grain of the film in flesh tones.

There are production hurdles too. Capturing—and holding—a tiny dot of ink on a rapidly moving piece of paper is the greatest challenge in printing. And the smaller the dot, the smaller the margin for error, every step of the way. That makes stochastic screens very unforgiving when they are on the press.

Virtually everyone who has used it says that doing stochastic printing right requires tighter controls than conventional screening.

Dot gain—the tendency for the size of the dot to become larger when it is printed—is another concern. While more dots equal more detail, more dots also equal less space between the dots and thus, less room to spare. Stochastic screens can experience as much as 20% more dot gain than traditional screens. To help control dot gain, it may be necessary to use a different reproduction curve than the one used with conventional screening techniques when the printer makes the plate. Different blankets and higher tack inks also may be required to control dot gain when the job is on-press.

Proofing remains something of a problem too. It’s important to start with good scans and calibrate the imager to ensure that the scan reproduces properly on press. Then the calibration must be changed for different press conditions or paper stocks. And remember that because the dots are so small, corrections can’t be made while the job is on-press. As some printers say, with stochastic, “the proof is the press check.” If any changes are required, so is a new plate.

Although some people think that stochastic is more forgiving when it comes to registration, that may not be entirely true. Stochastic printing can help to eliminate concerns about the misregistration of rosettes as well as lines hang-ing out, but maintaining good register is still important. Stochastic or not, misregistration will still blur the edges of fine lines and shift the color.

Printers also note that the quality of the paper stock is especially important. Ed thinks that is true for any project, but it may be especially important with stochastic screens. Smoothness counts more than ever, because even small imperfections in the surface can swallow the tiny dots. For those reasons some printers counsel against using stochastic methods with uncoated, or even matte coated, paper. A gloss coated paper will yield the best results.

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