Halftone Screens; Attributes; Screen Frequency - Lexmark Optra C710 User Manual

Halftone screens

Note: When printing color, you
cannot change the screen angle
settings. The reason for this is the
angles have been set to prevent
one color from over printing
another color.
Frequency
(cells per inch)

Screen frequency

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Chapter 4: Using color
The term halftone screen, refers to the pattern of dots applied to
an image. If you look closely at a black and white photograph in
a magazine, it appears to contain many shades of gray. If you
place the same picture under a magnifying glass, you see that it
is actually composed of a number of dots. These dots, also
known as pels, may be of varying sizes or varying tones. They
may also be the same sized dots applied to a tint of color. With-
out halftoning, it would not be possible to produce quality pho-
tographic images on a page printer. This process of representing
an image as a series of halftones, is known as halftone screen-
ing.
You can control the attributes for halftone screens by changing
the values to your halftone screen frequency and screen angle
settings. You can change these settings through the graphics tab
on your printer driver.

Attributes

Halftone screens have three main attributes. They are: screen
frequency, screen angle, and spot function. The halftone screen
is further divided into halftone cells. These cells contain the
Spot function
individual pel spaces. The screen frequency and angle attributes
determine both the number of halftone cells that make up a half-
tone screen and the orientation of the cell.
The spot function determines which of the individual pels in the
halftone cell is turned on to represent a particular gray level or
color tone. The illustration shows a halftone screen and halftone
cells rotated 45 degrees.
Angle
The screen frequency is the number of halftone cells per inch. A
larger number in the screen frequency increases the number of
halftone cells per inch. Increasing the number of halftone cells
per inch will not necessarily give you better quality. The reason
for this is the higher settings may make the colors or halftones
seem to run together or bleed.