Tilman Hausherr created PDFBOX-3897:
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Summary: Avoid sRGB self-conversions
Key: PDFBOX-3897
URL: https://issues.apache.org/jira/browse/PDFBOX-3897
Project: PDFBox
Issue Type: Improvement
Components: Rendering
Affects Versions: 2.0.7
Reporter: Tilman Hausherr
Assignee: Tilman Hausherr
Fix For: 2.0.8, 3.0.0
Attachments: PDFJS-6737-veryslow.pdf, PDFJS-8446-p1-slow.pdf
1)
PDICCBased.java detects if the colorspace is sRGB, but does not use this
advantage fully. {{toRGB()}} should return its argument when the colorspace is
sRGB.
The files from PDF.js issues 8446 and 6737 are much faster now. The speed
improvement can be experienced with files that use such pseudo ICC colorspaces
for shading, because there a large number of colors have to be converted.
2)
PDDeviceRGB.java also converts colors to itself. {{awtColorSpace}} is the sRGB
color space and so is {{/DeviceRGB}}, yet {{toRGB()}} calls
{{awtColorSpace.toRGB()}} instead of just returning its argument.
This second change does not have much influence on the speed of rendering on my
old computer (4 cores). But on the new computer (8 cores, 16 threads) the
complete rendering tests are now done in 300 instead of 400 seconds.
Rendering regression tests show a lot of small differences. I assume that
differences of 1/255 in a color somehow propagate and worsen, e.g. through
transparency layers. I looked at a few, the differences are detected by the
rendering tests but are invisible to my eye (in the diff file, the difference
can be made visible by setting Gamma to minimum). I've therefore increased the
tolerance to 3 units to avoid the work of analyzing hundreds of file
differences. Those that remain are still invisible to my eye, except
PDFBOX-3693-656282-p1-p8.pdf, which is very different but was different than
Adobe before (the whole file is very broken and the first page logs over 3000
errors). I suspect it is an incorrect RGB value that isn't clipped anymore now.
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