[Scribus] RGB Images & Transparency in PDF 1.4

[PLinnell]

On Friday 29 April 2005 23:56, Asif Lodhi wrote:
> Hi
>
> The "Adobe Acrobat" section of the "DTP ToolBox" node (under the
> "Hints for Scribus Users") of the Scribus documentation (that comes
> bundled with the Scribus 1.2.2cvs) says:
>
> "We are aware of one color mismatches with RGB images and
> transparency in PDf 1.4. Yes, this has been duly reported as a bug
> to Adobe too."
>
> Would you elaborate more on it?

It is simple to demonstrate. When you use single colors in vector 
objects and then give them some transparency, not all colors look 
correct when exported in PDF.1.4. I've not tested every version of 
Acrobat, but Reader 7 on Linux does not display correctly. Reader 
5.0.10 on Linux does.
>
> Does it imply that embedding non-transparent RGB images in PDF 1.4
> will not cause problems?

Should not be an issue.
>
> Do _indexed_ PNG images also come in the "RGB image" category?
> Personally, I suppose not because in common graphics software
> "indexed" and "RGB" are treated as two different modes. Please
> clarify if I am wrong.
>
Correct, there are even Indexed colors in CMYK.

> Does it imply that exporting a PDF 1.4 with embedded "indexed PNG"
> (with no transparency) images won't cause problems?
>
Not tested.
> Somewhere in the same node/section, the documentation says:
>
> "If you are creating Scribus files with transparency effects and
> export PDF 1.4 (PDF 1.3 does not support transparency), you can
> enable Show Transparency Grid. "

That's a feature of the Acrobat Reader. Look in the preferences under 
display.

> Does it mean that exporting PDF 1.3 from Scribus with embedded
> images, transparent or otherwise, won't cause problems -
> considering the text quoted earlier? Does it also mean that
> exporting PDF 1.3 with embedded RGB images, with or without
> transparency effects, will get rid of the bugs, mentioned in the
> text quoted earlier, altogether?
>
> Further, it would be of great help if the bug mentioned in the text
> quoted above could also be clearly explained further so that the
> documentation can be traced back to the original problem (and the
> related (original) causes as well) in addition to correlating the
> problem with similar problems being discussed on other mailing
> lists.
>

Nothing more than the particular combination of RGB vector images + 
transparency in PDF 1.4 in Reader 7. It is not an issue with Scribus, 
but Acro Reader 7. I've tested output from other apps. The issue is 
the same.

> Please elaborate.
>
> TIA
>
> Asif

Peter