KB73059536: FlexRip - How can I avoid broken dots in my screened output

Summary

Broken dots in screened output can result in bad prints and can be avoided in the design or by using the correct settings in the RIP.

Symptoms

Screened output sometimes show irregular shaped screening dots.

These irregular shapes are unwanted:

• Irregular dots have more dot gain than round dots with the same number of black pixels
• Sliced dots can be so small that they are washed away in plate making or worse, become unstable during printing.

Cause

Irregular dots occur when the original design contains too sharp or too small detail. This high-frequency detail can come from different sources:

• Too high detail in the design: Examples of this include
  • Screened text at 6pt
  • Screened hairy or noisy bitmaps
  • Very high resolution CT's with small and sharp detail
  • Screened hairlines, etc
• Sharp borders between neighboring pixels of a CT. If two neighboring pixels have a big difference in density, the border between them is a candidate for trouble.

Solution

Problems at pixel borders can be drastically improved by making the borders between pixels blurry instead of sharp. This is achieved by up-sampling the CT's with interpolation. This way big density-change is divided over several smaller steps. As a result the screening dots have a bigger tendency towards connected, round shapes.

In FlexRip 12, the Ripticket has options in the Expose panel (Advanced tab):

• Resample to automatic chosen resolution: reduces broken dot problems, by interpolating images to at least 1000 ppi.
• Resample to output resolution: calculate everything at output resolution, this gives the best results but is slower.

Workaround

For versions older than FlexRip 12, the same result from the above solution can be reached via the Contone Tuning tab in the FlexRip dispatcher (after switching on the tuning options):

• Enable contone scaling and set the CT resolution to a value of 100 dpi or higher. Using the output resolution will have the best result but is slow.