Question:

How can I avoid banding in graduated fills?

Answer:

Visable banding can be caused by several factors. Since we cannot control outside hardware related factors, we will address only the software factors. Realizing both hardware and software limitations, there will probably always be banding. The goal is to make any banding too small to see.

Postscript levels 1 and 2, the software environment many are still in, can only describe 256 shades of gray, so blends can only have 256 or fewer steps. If you divide the length of the blend by the number of steps you will get the size of each step. Steps of 1 point or less are usually too small to be noticed. At coarser line screens (85 line or lower) even 2 point steps will probably not cause noticeable banding.

If a gradation does not use the full range of 256 shades or levels of gray, you increase the likelihood of visible banding. There are several reasons you might not get 256 shades of gray.

First, you get the maximum 256 shades from 0% to 100%, so if the blend is from 30% to 50%, you only get 51 shates. This applies to each color in a CMYK blend, so if you blend from 100C-50M-30Y-20K to white only Cyan will get the full range. Fortunately, one smooth dominant process color is aften enough to hide banding in the other three colors.

Second, the resolution must be 16 times the final line screen or there are not enough dots to create the 256 levels of halftone dots. (A square 16 dots by 16 dots has 256 possible dots in it, thus 256 levels of gray).

Finally, the settings for the target printer resolution in the software application you are using (Illustrator, Freehand, etc.) can affect the number of steps in the blend when you save the EPS file.

You may have heard that Photoshop blends are "smoother" than some other applications. This may be true because there is an option to "dither" the rows of dots via blurring tools to make them appear smoother. These files are, however, significantly larger.

With the advent of Postscript level 3, we can now create vector based gradations and blends directly in programs like Quark and Illustrator, and the results will be almost perfectly smooth, provided the output devise and all related software are Postscript level 3 compatible

Where possible, we recommend Postscript level 3 as the best solution for banding.

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