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Reassurance - PS CMYK and RGB images, latex document, PDF target
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| Colin Brough 2006-03-28, 7:01 pm |
| I'm trying to understand how 'convert' from ImageMagick encodes RGB
and CMYK images - and consequently how a LaTeX file that incorporates
such an image and is then translated into a PDF will end up...
I'm wanting to end up with a CMYK PDF I can send to a commercial
printer for printing. I understand I need to convert images to CMYK
PostScript before inclusion, and that latex/dvips/ps2pdf or whatever
toolchain should keep the final image CMYK. So far, so good.
However, when I looked at what:
convert file.jpg -colorspace CMYK file.ps
produces, I don't understand how a subsequent program can tell that
the data is in CMYK colorspace! The PS header for both RGB and CMYK
images is identical, just the data portion differs:
http://www.colinbrough.pwp.blueyond...Flame01-cmyk.ps
http://www.colinbrough.pwp.blueyond...eFlame01-rgb.ps
How can my printer's preflight tools check whether such images (or
PDFs produced using them) are CMYK or RGB? I'm  !
FU's set to comp.lang.postscript, in case anyone wants to follow this
having seen it in one of the other groups.
Cheers
Colin
--
----------------------------------------------------------------------
Colin Brough Colin.Brough@blueyonder.invalid
(Replace .invalid with .co.uk to reply)
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| Aandi Inston 2006-03-28, 7:01 pm |
| Colin Brough <Colin.Brough@blueyonder.invalid> wrote:
>I'm wanting to end up with a CMYK PDF I can send to a commercial
>printer for printing. I understand I need to convert images to CMYK
>PostScript before inclusion, and that latex/dvips/ps2pdf or whatever
>toolchain should keep the final image CMYK. So far, so good.
Well, not necessarily. Some printers, especially in the US, require
CMYK. Others prefer tagged RGB and some might require this, since it
is hard for you to do an accurate CMYK conversion without knowledge of
their press. Always ask what is required.
>
>However, when I looked at what:
>
> convert file.jpg -colorspace CMYK file.ps
>
>produces, I don't understand how a subsequent program can tell that
>the data is in CMYK colorspace! The PS header for both RGB and CMYK
>images is identical, just the data portion differs:
In general you can't tell the color space except by interpreting the
PostScript file. In this case, I have: both PostScript files contain
RGB images.
----------------------------------------
Aandi Inston quite@dial.pipex.com http://www.quite.com
Please support usenet! Post replies and follow-ups, don't e-mail them.
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| Helge Blischke 2006-03-28, 7:01 pm |
| Colin Brough wrote:
>
> I'm trying to understand how 'convert' from ImageMagick encodes RGB
> and CMYK images - and consequently how a LaTeX file that incorporates
> such an image and is then translated into a PDF will end up...
>
> I'm wanting to end up with a CMYK PDF I can send to a commercial
> printer for printing. I understand I need to convert images to CMYK
> PostScript before inclusion, and that latex/dvips/ps2pdf or whatever
> toolchain should keep the final image CMYK. So far, so good.
>
> However, when I looked at what:
>
> convert file.jpg -colorspace CMYK file.ps
>
> produces, I don't understand how a subsequent program can tell that
> the data is in CMYK colorspace! The PS header for both RGB and CMYK
> images is identical, just the data portion differs:
>
> http://www.colinbrough.pwp.blueyond...Flame01-cmyk.ps
> http://www.colinbrough.pwp.blueyond...eFlame01-rgb.ps
>
> How can my printer's preflight tools check whether such images (or
> PDFs produced using them) are CMYK or RGB? I'm !
>
> FU's set to comp.lang.postscript, in case anyone wants to follow this
> having seen it in one of the other groups.
>
> Cheers
>
> Colin
>
Searching ImageMagick's web site revealed the suggenstion:
convert source_image eps2:destination.eps
(or eps3 instead of eps2). But I haven't tried it.
Helge
--
Helge Blischke
Softwareentwicklung
SRZ Berlin | Firmengruppe besscom
http://www.srz.de
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| [jongware] 2006-03-28, 7:01 pm |
| "Colin Brough" <Colin.Brough@blueyonder.invalid> wrote in message
news:s13of3-r6e.ln1@brough.bd...
> I'm trying to understand how 'convert' from ImageMagick encodes RGB
> and CMYK images - and consequently how a LaTeX file that incorporates
> such an image and is then translated into a PDF will end up...
>
> I'm wanting to end up with a CMYK PDF I can send to a commercial
> printer for printing. I understand I need to convert images to CMYK
> PostScript before inclusion, and that latex/dvips/ps2pdf or whatever
> toolchain should keep the final image CMYK. So far, so good.
>
> However, when I looked at what:
>
> convert file.jpg -colorspace CMYK file.ps
>
> produces, I don't understand how a subsequent program can tell that
> the data is in CMYK colorspace! The PS header for both RGB and CMYK
> images is identical, just the data portion differs:
>
> http://www.colinbrough.pwp.blueyond...Flame01-cmyk.ps
> http://www.colinbrough.pwp.blueyond...eFlame01-rgb.ps
> How can my printer's preflight tools check whether such images (or
> PDFs produced using them) are CMYK or RGB? I'm !
Me too. I created PDFs of both, using Leave Color Unchanged. Both images are
reported to be RGB, although the one you call 'CMYK' lost some data in
translation.
Looking at the PS, both images have their data stored as RGB -- see the
definition of DirectClassImage, which uses DirectClassPacket to read; that
one reads red, green, blue.
I'd guess it gets translated *twice*, once RGB to CMYK, then again to RGB.
[Jongware]
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| Roger Willcocks 2006-03-29, 4:03 am |
| "Colin Brough" <Colin.Brough@blueyonder.invalid> wrote in message
news:s13of3-r6e.ln1@brough.bd...
> I'm trying to understand how 'convert' from ImageMagick encodes RGB
> and CMYK images - and consequently how a LaTeX file that incorporates
> such an image and is then translated into a PDF will end up...
>
> I'm wanting to end up with a CMYK PDF I can send to a commercial
> printer for printing. I understand I need to convert images to CMYK
> PostScript before inclusion, and that latex/dvips/ps2pdf or whatever
> toolchain should keep the final image CMYK. So far, so good.
If your source images really are RGB, you would do better to use a
CIEBasedABC colo(u)rspace with an sRGB profile (see PLRM III
p. 225). That way the print engine can do an accurate conversion
to CMYK, taking into account the press characteristics.
--
Roger
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| George N. White III 2006-04-02, 8:01 am |
| On Wed, 29 Mar 2006, Roger Willcocks wrote:
> "Colin Brough" <Colin.Brough@blueyonder.invalid> wrote in message
> news:s13of3-r6e.ln1@brough.bd...
The o.p. seems to be under a misconception that you have to go thru
EPS to get PDF's from LaTeX. There is a workflow that does not require
EPS files based on pdflatex.
[color=darkred]
> If your source images really are RGB, you would do better to use a
> CIEBasedABC colo(u)rspace with an sRGB profile (see PLRM III
> p. 225). That way the print engine can do an accurate conversion
> to CMYK, taking into account the press characteristics.
The printer we use was asking for sRGB PDF's a few years ago, but now they
want CMYK PDF's. The problems for a commercial printer with sRGB include
a) many customers who don't understand that a printer can't reproduce some
of the colors they can get on a screen and b) the large number of crappy
applications that don't support CMYK and do produce low quality output.
Requiring customer CMYK pdf's acts as a filter to weed out "difficult"
customers.
--
George N. White III <aa056@chebucto.ns.ca>
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