The frequency of the halftone dots - their density within a given area - is an important number. In the United States, we measure halftone screens in "lines per inch" or lpi. If the "linescreen" [a.k.a. "screen frequency"] is 100 lpi, then each square inch of a given color will contain 100x100=1,000 halftone dots. Different printing techniques and conditions require different halftone screens (note: these numbers are typical, not hard and fast)
- Newspapers: 85-100 lpi
- CDs (on-disc screen printing): 85-100 lpi
- Magazines: 133-175 lpi
- CD packaging (paper products): 150 lpi
- Art books: 175 lpi
Unfortunately, the computer monitor that you're reading this on is a low-resolution device, and is incapable of resolving the fine detail that would reveal the difference between typical printed linescreens. If you have a newspaper and a magazine handy, examine photographs in both of them closely. Use a magnifying glass, if one is available. This exaggerated illustration shows you what to look for. |
