[NTG-pdftex] [ pdftex-Bugs-723 ] Pale colors when using transparency in PNG graphics

noreply at sarovar.org noreply at sarovar.org
Fri Jan 26 07:07:02 CET 2007


Bugs item #723, was opened at 2007-01-25 06:27
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Category: Image inclusion
Group: v1.40.1
Status: Open
Resolution: Accepted
Priority: 5
Submitted By: Mark Henning (markhe)
Assigned to: Martin Schröder (oneiros)
Summary: Pale colors when using transparency in PNG graphics

Initial Comment:
Hi at all!

I hope this is the right place to report this problem:

If there is any transparency definition in a PNG file 
(e.g. transparency by a certain color or given by a 
mask), then all graphics on the page show pale colors. 
Graphics on pages before or after this page show normal 
colors. This is confirmed in several versions of Adobe 
Acrobat Reader. Ghostview/Ghostscript does not show 
this behaviour. The reason for this viewer-dependency 
might be a missing transparency-definition in the PDF 
file which makes it ambiguous, as reported by Andreas 
Lobinger in de.comp.text.tex; thread "Blasse Farben bei 
transparentem PNG in pdftex".


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>Comment By: Mark Henning (markhe)
Date: 2007-01-26 06:07

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O.K., there are readers showing the problem and readers not 
showing the prob. There are two possibilities for that:

a) The generated PDF is O.K. and there is a bug in the Adobe 
Reader.

b) The generated PDF is ambiguous (as mentioned by Andres 
Lobinger; I previously told) and it depends on "internal 
defaults" of the reader whether the bug shows up or not.

Finally, the answer can only be found within the generated 
PDF and a comparison with the PDF specs. Unfortunately, I 
have absolutely no idea about the internals of PDF.

In the usenet post <ep7at4$d87$1 at daniel-new.mch.sbs.de> from 
Andreas Lobinger he told how he looked into the PDF (maybe 
this helps):

Basis: http://sourceforge.net/projects/pdfplayground/

Script:
#!/usr/bin/env python
import sys
sys.path.append("/homes/lobingera/Sources/PostPdf/
pdf031205")

import pdftool
import pdfo

x,t,r = pdftool.pfile(sys.argv[1])

print "trailer"
print pdftool.printall(t)

for a in x.allused():
    n1 = pdfo.pdfo(a,x.getgen(a))
    n1.content,n1.stream = pdftool.pxobj(r,x,a)

    print n1.show('toscreen')


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Comment By: Martin Schröder (oneiros)
Date: 2007-01-25 17:05

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Attached the results of rendering this with two professional
RIPs (Jaws and Harlequin). I don't see it there...

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Comment By: Martin Schröder (oneiros)
Date: 2007-01-25 15:15

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Ah, now I see it. Inded, AR7.0.9 shows a difference.
The problem also shows with files generated by pdftex 1.40.1

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Comment By: Mark Henning (markhe)
Date: 2007-01-25 15:08

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Sorry; I forgot to check the checkbox for uploading the 
file.

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Comment By: Mark Henning (markhe)
Date: 2007-01-25 15:06

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I rechecked with Adobe Acrobat 7.0 and Adobe Acrobat 7.0.9 
on Win2000 SP4, both showed the color differences (see the 
PNG file I uploaded. It shows a direct comparison.). If you 
checked the PDF and say that it is O.K., then there must be 
a bug in Adobe Reader. I will contact Adobe then.


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Comment By: Martin Schröder (oneiros)
Date: 2007-01-25 13:53

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I see no problems with AR 7.0.9, kpdf 0.5.1 and gs 8.54 on
SUSE 10.1.

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Comment By: Martin Schröder (oneiros)
Date: 2007-01-25 13:51

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Pointer to the threat on dctt:
http://groups.google.de/group/de.comp.text.tex/browse_thread/thread/758dcc47273b4e7d/

An example:
http://www.homolog.de/temp/PNGTransparencyBug.zip

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