Solid screening is a technique that reduces ink consumption (and associated costs) by punching holes – too small to be seen in the presswork – into graphics that normally would print as a solid 100% tone or color. This technique is best suited for newspaper printing where the combination of dot gain and absorbency of the paper hide the visibility of the holes in the final presswork.
In this example I've used the character "$" from the Bitstream "Vera" font**, however this technique can be used with any line/solid graphic. In order to create the holes, I've screened the letters from 100% solid to a 90% tone. The correct amount of screening back to use requires some experimentation as it is a function of the halftone screening and paper that is being used.
A - The original character (Bitstream Vera) at 10 pt.
B - The same character using the SPRANQ Ecofont*. This font is designed with holes within the letters to reduce inkjet ink consumption by approximately 15-20%. The font can also be used for offset printing, however, because of the size of the holes used, this font is limited to a maximum character size of about 12pt.
C - The same character but screened back to 90% using a 133 lpi AM halftone. Because the AM dot is quite coarse, this technique is best suited to sans serif sizes greater than 18 pt. otherwise the character become too broken up by the halftone screening.
D - The same letter but screened back to 90% using a 20 micron FM halftone. The high resolution FM dot allows this technique to be used with both serif and sans serif fonts ranging from about 9pt and larger.
For newspaper application, rather than using a halftone to screen back type, it may instead be worthwhile to develop a custom font or to modify the current publication font(s), and build holes directly into the characters in similar fashion to example "B" above.
* The SPRANQ Ecofont can be downloaded from: http://www.ecofont.eu/
** The Bitstream Vera font can be downloaded from: http://www.dafont.com/bitstream-vera-mono.font
Screening solid tone areas in order to reduce ink usage is not limited to flat tone areas or fonts (as described in part 1), the technique can also be used on halftones which are, after all made up of small areas of solid tone. Here is the original image of comedian Tony Hancock:Here is a close up of the original AM/XM halftone version of the image; (Click images to enlarge)
Here is the AM/XM halftone rescreened with a 2% AM halftone dot (applied to tones darker than 5%):A more sophisticated version of this method is used in Esko Concentric screening:
And here is the AM/XM halftone rescreened with a 2% FM dot (applied to tones darker than 5%):
Punching holes into halftones does add complexity in prepress and may not be possible with some workflows. However, it can be a useful strategy to reduce ink consumption in both black and white and color images for those systems that are able to screen bilevel halftones.