From a136c6faa5991fbfc60c64998da50e26a8f6660c Mon Sep 17 00:00:00 2001
From: Jeremias Maerki
+ Since Apache FOP supports the collapsed border model, every border segment consists + of two separate shapes. This is due to the fact that each side of the border + segment can have a different color. Now, Adobe Acrobat may display thin (1 pixel wide) + lines inside the border segment or sometimes even between to adjacent + colored rectangles making up the background of a block or table cell. + This effect is due to the way Adobe Acrobat does anti-aliasing. Adobe's algorithm + seems to cause these artifacts. Other PDF viewers don't have that problem. Or at least + we haven't had any reports in that direction. +
++ First of all, these artifacts do not appear in print since no anti-aliasing is done + by Adobe Acrobat in this case (except maybe if you tell Acrobat to print the page + as a bitmap in which case Adobe fully composes the page itself). So, if the artifacts appear + on screen, it doesn't mean they have to appear in print, too. +
++ To get rid of the artifacts, you can call up the "Preferences" dialog of + Adobe Acrobat and select the tab "Page display". Enabling "Enhance thin lines" + may help in some situations. Otherwise, you can disable "Smooth line art". + You may have to disable "Use 2D graphics acceleration", too, so you can disable + "Smooth line art" in the first place. +
++ Here an example of how the effect can look like (left: anti-aliasing on, right: anti-aliasing off): +
+ ++ Unfortunately, it is not possible to control the above settings from within the PDF file. + The user has to change these settings himself. Improving FOP to avoid this kind of problem + would be possible although rather hard to achieve because we'd need to add a considerable + amount of code to combine the various line segments. Something like that has been tried already + years ago showing that this is a tricky task. Also, the improvement may not justify the amount + of effort required. +
+