Troubleshooting > Troubleshooting printing > Minimizing banding |
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Minimizing banding
Banding can occur when printing imported bitmap images, blends, and gradient fills.
To smooth a color transition, increase the printer resolution and decrease screen ruling; refer to the smoothness formulas that follow.
To print blends and gradient fills without banding, follow these guidelines:
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For imported bitmap images, resize them automatically in increments based on the selected printer's resolution by pressing Shift+Alt (Windows) or Shift+Option (Macintosh) while dragging the image's corner handle. |
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For a PostScript Level 2 output device, use a blend instead of a Gradient fill and specify the appropriate number of steps indicated by the N=(P/R)2 smoothness formula (see Smoothness formula for banding). |
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For a blend, before creating the blend, specify the resolution of the final output device or specify blend steps in the Object inspector. (Switching to a different output device or changing the printer resolution value doesn't change the number of tints in the blend.) |
You can also use the Find & Replace Graphics feature to automatically recalculate blends for different printer resolutions. |
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For spot-to-spot blends and spot-to-spot gradient fills, set appropriate halftone angles for each spot color in the blend or gradient fill in the Separations panel in the Print Setup dialog box. Undesirable moiré patterns will result if you overprint a spot color on top of another when the halftone angles are set incorrectly. |
Smoothness formula for banding
For process colors, up to four inks describe the color at the each end of a transition, and each ink has its own degree of banding. Calculate the tint band size for the most visible inkusually black or magenta. Narrower bands create smoother transitions. A size of 0.05 points or less is required for high quality output. For less exacting output, tint bands of 1 to 2 points may be acceptable.
Use these formulas to determine the optimum values to minimize banding when printing color transitions.
N= (P/R)2
where N is the number of tints the output device can produce, measured as P for the printer resolution (P) divided by R for the screen ruling, squared.
T= N * Z
where T is the actual number of tints available, measured as N for the printer's number of tints available, multiplied by Z for the percentage difference between colors expressed as a decimal value (for example, 5% = 0.05).
S= D/T
where S is the size of each tint band in a color transition, measured as D for the distance between colors, divided by T, the number of tints available.
For process colors, up to four inks describe the color at each end of a transition, and each ink has its own degree of banding. Calculate the tint band size (in points) for the most visible ink usually black or magenta. Narrower bands create smoother transitions. A size of 0.05 points or less is required for high quality output. For less exacting output, tint bands of 1 to 2 points may be acceptable.
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