valerybokov commented on PR #491:
URL: https://github.com/apache/pdfbox/pull/491#issuecomment-5128009305

   > This change produces a white line in the rendering of the file from 
PDFBOX-5403, in the text "Enzian Immobilien".
   > 
   > update: I tried "fix 1" alone and had just that.
   
   Root cause: the alpha-combine fix (fix 1) correctly exposes any place where 
the pattern's own alpha isn't fully opaque — but TilingPaint has hairline 
(1-pixel), fully-transparent seams at tile boundaries from sub-pixel rounding, 
which used to be invisible (the old code just overwrote alpha with the mask's, 
ignoring the paint's). In the PDFBOX-5403 file, a pattern is tiled across many 
repeated ~14pt-tall bands (one per text line), and the seam lands right in the 
middle of each line, showing as a light gray/white streak through the text.
   
   Fix: before combining, widen the paint's own alpha to the max of its 
4-neighbors (a 1px dilate) — absorbs hairline seams while leaving genuinely 
large gaps (many pixels wide, like the original PDFBOX-6077 case) untouched.


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