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https://issues.apache.org/jira/browse/PDFBOX-3000?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15807569#comment-15807569
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Tilman Hausherr edited comment on PDFBOX-3000 at 1/7/17 2:24 PM:
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I found out from Boris Aronshtam and Dr. Paul Jones why the blending files
don't render properly:
http://www.pdfvt.com/PDFVT_TransparencyGuide.html
{quote}
It is wrong to treat the page background as a separate color. Page background
is not a color, but the unmarked space.
...
blending with the background ignores the blend mode, and is equivalent to
blending with BM=Normal against the opaque white color.
{quote}
We use a white page background, and we don't know about "unmarked space". Java
does not have such a concept AFAIK. Doing a "Screen" blend against white
background brings a white result.
The attached file gs-bugzilla689931_reduced-ScreenBlendPageBackground.pdf shows
a small white rectangle in a blue rectangle with Adobe Reader. The white area
is because I filled a white rectangle there; in the rest I did nothing thus the
difference. PDFBox treats all as white background so it displays the whole PDF
as white. Adobe treats the outside as "unmarked space" so it just copies and
the inside as "white" so the screen blend result is white.
Mitigation:
- most files have "Multiply" blend mode which doesn't bring this effect
- most files wouldn't use any "interesting" blend modes against the paper
background because it wouldn't make any difference
was (Author: tilman):
I found out why the blending files don't render properly:
http://www.pdfvt.com/PDFVT_TransparencyGuide.html
{quote}
It is wrong to treat the page background as a separate color. Page background
is not a color, but the unmarked space.
...
blending with the background ignores the blend mode, and is equivalent to
blending with BM=Normal against the opaque white color.
{quote}
We use a white page background, and we don't know about "untouched" space. Java
does not have such a concept AFAIK. Doing a "Screen" blend against white
background brings a white result.
The attached file gs-bugzilla689931_reduced-ScreenBlendPageBackground.pdf shows
a small white rectangle in a blue rectangle with Adobe Reader. The white area
is because I filled a white rectangle there; in the rest I did nothing thus the
difference. PDFBox treats all as white background so it displays the whole PDF
as white. Adobe treats the outside as "undefined" so it just copies and the
inside as "white" so the screen blend result is white.
Mitigation:
- most files have "Multiply" blend mode which doesn't bring this effect
- most files wouldn't use any "interesting" blend modes against the paper
background because it wouldn't make any difference
> Transparency Group issues
> -------------------------
>
> Key: PDFBOX-3000
> URL: https://issues.apache.org/jira/browse/PDFBOX-3000
> Project: PDFBox
> Issue Type: Bug
> Components: Rendering
> Affects Versions: 2.0.0
> Reporter: John Hewson
> Fix For: 2.1.0
>
> Attachments: 007087-payment-due-p58_reduced2.pdf, BlendModes-rgb.pdf,
> PDFBOX-1697-reduced-rotations.pdf, PDFBOX-2182_mod.pdf, PDFBOX-3400-RGB.pdf,
> PDFBOX-3494_reduced.pdf, PDFBOX-3494_reduced_cropX.pdf, PDFBOX-3564-Mask.pdf,
> PDFBox3359PanelTestEnhanced.java, PDFJS-2845-p1.pdf,
> PDFJS-5811-2-p3_reduced.pdf, PDFJS-5811-2-p3_reduced4.pdf,
> PDFJS-5811-2-p4_reduced-rotations.pdf, PDFJS-5811-2.pdf,
> PDFJS-5853_reduced.pdf, PDFJS-6967_reduced_outside_softmask.pdf,
> SoftMask-Clipped.pdf, SoftMask.pdf, blendmodes.pdf, circle-simple.pdf,
> ds-firewall-enterprise-p1_reduced.pdf, gs-bugzilla689309-reduced-bc0.pdf,
> gs-bugzilla689309-reduced-bc1.pdf, gs-bugzilla689309-reduced.pdf,
> gs-bugzilla689931_reduced-Multiply.pdf, gs-bugzilla689931_reduced-Screen.pdf,
> gs-bugzilla689931_reduced-ScreenBlendPageBackground.pdf,
> gs-bugzilla691157.pdf, gs-bugzilla691157_mod_unc.pdf,
> gs-bugzilla691157_mod_unc.png, gs-bugzilla691348.pdf,
> gs-bugzilla691650-2.pdf, gs-bugzilla692217_reduced.pdf,
> gs-bugzilla693322_reduced.pdf, gs-bugzilla694556-3.pdf,
> gs-bugzilla695354.pdf, gs-bugzilla695582-transparency-fill-stroke.pdf,
> gs-bugzilla695582-transparency-fill-stroke.pdf-1.png,
> samsung_galaxy_s_4_um-p1_reduced.pdf, snowman-nose-gradient-rgb.pdf,
> snowman-nose-gradient-rgb_reduced-0.6-bad2.pdf,
> snowman-nose-gradient-rgb_reduced-0.7-good2.pdf,
> snowman-nose-gradient-screenshot-comparison-11.12.2016.jpg,
> snowman-nose-gradient.pdf, snowmen-opacity-clipping-masks-2.0.3.png,
> snowmen-opacity-clipping-masks-2.1-SNAPSHOT-10.12.2016.png,
> snowmen-opacity-clipping-masks-2.1.0-SNAPSHOT-2016-12-07.png,
> snowmen-opacity-clipping-masks-adobe-illustrator.png,
> snowmen-opacity-clipping-masks.pdf, softmask-rewrite-alt1.patch,
> softmask-rewrite.patch
>
>
> This is a follow-up issue for transparency group issues from PDFBOX-2423.
> More details to come.
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