Halftone Info

Halftones are made up of groups of spots, some larger and some smaller. Each spot is in a cell made up of printer dots.

Halftone cells are arranged in a pattern that has three primary attributes:

1. Frequency:
   In a halftone there are so many spots to count, it is simplified by counting lines or rows of spots per inch. Lines-per-inch or lpi: The lower the screen frequency, the coarser the screen. The cells are bigger and the image is rougher looking.
2. Angle: (or screen angle)
   The lines or rows of spots in the halftone screen is often turned to a 45 degree angle because that angle fools our eye best into seeing gray instead of a pattern of dots. Other angles are good for special effects and color separations.
3. Spot Shape:
   You almost never notice the shape of a halftone spot unless the screen frequency is really low ie. (10-lpi). In a 133-lpi screen each cell is so tiny (1/133 of an inch) you can barely see what it looks like but choosing the shape of the spot (for example, square or elliptical) can make a difference in the appearance of the halftone (contrast or smooth gradations).
   • Spot Size:
     Recently, many laser printers on the market can produce variable sized laser dots. Apple's PhotoGrade technology provides more gray levels at a given screen frequency and output resolution for example 91 gray levels with a 106-lpi screen frequency at 300-dpi.