Adobe Illustrator CS4 - Manual (Page 426)

419 USING ADOBE ILLUSTRATOR CS4
Printing
Setting the proper screen frequency for printing gradients, meshes, and
blends
When printing your file, you may find that the resolution of your printer, when combined with the chosen screen
frequency, allows fewer than 256 levels of gray. A higher screen frequency decreases the levels of gray available to the
printer. For example, if you are printing at a resolution of 2400 dpi, using a line screen higher than 150 results in fewer
than 256 levels of gray. The following table lists the maximum line-screen setting you can use with printers to maintain
all 256 levels of gray:
See also
“ Change the printer resolution and screen frequency ” on page 408
Calculate the maximum blend length for gradients
Illustrator calculates the number of steps in a gradient based on the percentage of change between the colors in the
gradient. The number of steps, in turn, determines the maximum length of the blend before banding occurs.
1 Select the Measure tool , and click the beginning point and the endpoint of the gradient.
2 Note the distance displayed in the Info panel on a piece of paper. This distance represents the length of the gradient
or color blend.
3 Calculate the number of steps in the blend using this formula:
Number of steps = 256 (number of grays) X Percentage change in color
To figure out the percentage change in color, subtract the lower color value from the higher color value. For example,
a blend between 20% black and 100% black is an 80%—or 0.8—change in color.
Final Imagesetter Resolution Maximum Line Screen to Use
300 19
400 25
600 38
900 56
1000 63
1270 79
1446 90
1524 95
1693 106
2000 125
2400 150
2540 159
3000 188
3252 203
3600 225
4000 250