DOT GAIN

Dot gain on our coldset open web press varies between 15-20%. On some types of paper dots often appear larger than they should, causing loss of detail and darker tones than desired. This dot gain can be compensated for in the film stage by reducing the size of the film dot. Dot compensation may be varied in different areas of the image, with less compensation in highlight areas and greater compensation in shadow areas.

A Common Question:
Why are we getting color variation during a press run?

Answer:
Lots of things!
Dot gain is the primary cause as a result of variation in ink feed or printing pressure. Ink trap can be a culprit when the ink film thickness of the second down ink varies. On longer press runs, changes in pressroom humidity will change ink/water balance thus affecting color. Ink absorption by the paper can also vary, ( and with it the color) if the paper was sheeted from multiple rolls. Absorption differences are also seen from the felt to the wire side of the sheet which produce variation on backup.

Controlling Dot Gain
Dot gain can be controlled halftones by varying dot size reduction in different image areas. Often a dot no longer than a pinpoint is called for in highlight areas. Be sure to adequately compensate for dot gain...if dot size is not reduced sufficiently, dots run together and a condition known as plugging occurs. This results in overly dark, muddy shadow areas. Overcompensation for dot gain (reducing the dot size too much) must also be avoided. Overcompensation causes gray-out - a condition in which the image appears weak and washed out.