[poppler] pdftops : issue with colorspaces with some printers (gray vs rgb)

[William Bader]

I think that the cause is a patch that I submitted in May 2011 around the time of poppler 0.17.0.
Search for isGray in poppler/PSOutputDev.cc
I use pdftops to make postscript files that will be printed on a newpaper press.
My application was being sent PDFs with embedded logos that looked gray but were actually in RGB color space, and they were not getting separated correctly on color pages.
I added a check in PSOutputDev that if every pixel of a RGB bitmap was equal R, G, B, it will be written as a grayscale bitmap, which fixed my separation problems and made the files smaller.
If that makes a problem for you, it should be possible to add a command line option to control the RGB to grayscale conversion, maybe similar to some of the distiller options in ghostscript http://ghostscript.com/doc/current/Ps2pdf.htm
William

Date: Wed, 4 Feb 2015 16:18:59 +0100
From: benjamin.lefevre at photobox.com
To: poppler at lists.freedesktop.org
Subject: [poppler] pdftops : issue with colorspaces with some printers (gray	vs rgb)

Hi everyone,
My name is Benjamin and I am french.
I'm new on this mailing list :)
 I come to you for a question or maybe for a feature request (at this stage, I'm not sure).
Please look at this pdf (dropbox: https://www.dropbox.com/s/yoj6h3o4irnlgun/source.pdf?dl=0 )
There are two monochrome images (in DeviceRGB in the pdf).
After executing 'pdftops', the images are cut in half, with the top part in DeviceRGB and the bottom in DeviceGray. This causes colorimetric issues on some of my printers (most of them in fact).
Is it possible to preserve DeviceRGB by executing pdftops? I did not manage to achieve it with the few available options provided by pdftops.....Or would it be possible to have a new option in poppler (pdftops in my case) to preserve colorspaces, and to not optimize the monochrome images in DeviceGray? 
Thank you in advance,
Benjamin.





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