[Poppler-bugs] [Bug 46600] [patch] pdftops git 25Feb12 restore deleted binary code and level2sep fixed

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=46600

--- Comment #4 from William Bader <williambader at hotmail.com> 2012-02-25 09:20:04 PST ---
Thomas,

>As far as I can see the detection, if a cmyk image is contains only gray
values, is wrong

It is necessary for my application.
I sometimes get PDFs that contain embedded images which are meant to be gray
but for some reason (I suspect being copied from an RGB logo meant for the
web), pdftops -level1sep generates gray with C=M=Y=gray level, K=0 instead of
C=M=Y=0, K=gray level.  When I separate it for printing on a press, it makes C,
M and Y plates instead of a single K plate.  Often no one notices until almost
the print deadline, and then they have to rush to rebuild the PDF and push it
back through the application to generate a new page.
My CMYK to gray change solves that problem.  It is necessary for my application
and probably useful for anyone else who will need to do color separations on
output from pdftops.
If you think that it is wrong for overprinting, then I can add a command line
option to enable it, or I can disable it when -overprinting is specified.
Do you have a PDF with overprinting that doesn't work with my change?
I think that printing gray images a K instead of as a mix of CMY should improve
the overprinting situation because adjacent C, M or Y can be overprinted onto K
if necessary, and printing K as a combination of CMY creates registration
issues, especially with small text, and ink coverage levels at dark shades of
gray.

>But probably we never will run in a situation where a CMYK image will contain
only values where C = M = Y

That is one of the reasons why I think that the change is relatively safe.  The
image probably comes from a gray or black web image like a gif for a company
logo that was created in RGB and then embedded into a PDF.  The image really
should be black or gray.

William

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