[pdftex] Decode issue

Thanh Han The hanthethanh at gmail.com
Sat May 5 09:26:23 CEST 2007

I had problem sending this mail and try it again, so my
apologize to people who receive this mail twice.



I looked into the sources. The Decode array insertion is
hardcoded whenever a jpeg image with colorspace CMYK is included.
The support of additional colorspace was added by request of Hans
Hagen IIRC, he needed a mean to change the default colorspace of
images. So it was done with this assumption: if someone supplies his
own colorspace, he is responsible for everything related.

I am not sure what can be done with this, since it's hard to define
the right behaviour of pdftex in this situation. My vote is to leave
things as they are, and document relevant issues in the manual.


PS: I uploaded the test files here: http://www.sendspace.com/file/rc04al

On Thu, May 03, 2007 at 08:48:10PM +0200, Pawel Jackowski wrote:
> Hi!
> While making a sample for Jano in BachoTeX I've found the following
> issue. Please consider the attached example.
> pdfTeX automatically recognizes embedded JPEG colorspace. I guess it
> also reads decoding parameters from the image and (re)inserts them to
> PDF if necessary; in the first case one may see
> 	/ColorSpace /DeviceCMYK
> 	/Decode [1 0 1 0 1 0 1 0]
> key in XObject dictionary. Once the user povides 'colorspace' keyword,
> no /Decode is inserted, that (may) result in negative output, as in
> example. Obviously one can insert decoding as a custom image attribute,
> but one cannot control what is the proper decoding.
> This happens for all cmyk jpegs from photoshop.
> Cheers,
> --
> Pawe/l Jackowski
> GUST, Poland
> P.Jackowski at gust.org.pl
> www.pawcoo.com
> www.acchsh.com

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