When saving a CMYK file to JPG, PIL seems to invert the colors.  I've 
submitted a patch to Fredrik already for this, and it should be in the next 
major build.

Adding a simple invert to the image before saving will help.

Kevin.
----- Original Message ----- 
From: "abel deuring" <adeuring@[...].net> 
To: "Cesare Leonardi" <ced@[...].com> 
Cc: <image-sig@[...].org> 
Sent: Thursday, April 13, 2006 1:58 PM
Subject: Re: [Image-SIG] Problem with JPEG and CMYK color space


>  Cesare Leonardi wrote:
> > Berni CED ha scritto:
> >>I have encountered several images that are not managed well by PIL.
> >>Exactly as explainded by the following old mail (which had received no
> >>reply) colors are darker and, in general, different from the original:
> >>http://mail.python.org/pipermail/image-sig/2001-July/001514.html
> >>And like in that mail, my problematic images have one thing in common:
> >>they are JPEG using the CMYK color space. JPEG in RGB are elaborated
> >>correctly.
> >
> > No one can confirm or add some info? It's a known problem? Fredrik?
> 
>  Cesare,
> 
>  I can confirm the problems, though I have no idea, why the files
>  written by PIL have completely wrong colours.
> 
>  Regarding the altered colours of the image displayed by im.show()
>  [disclaimer: I'm writing this without actually having a look into
>  the PIL sources, so I can easily be wrong...]: The changes are
>  probably caused by a very simple conversion from CMYK to RGB, like
>  C = 1 - R, M = 1 - G, Y = 1 - B. Both CMYK and RGB are device
>  dependant color spaces, i.e., if you use two different monitors, and
>  let them display some pixels with identical RGB values, the
>  displayed colours are not exactly identical. The same holds for CMYK
>  colours: Two different ink jet printers will most likely show
>  slightly different colours for the same CMYK value. And offset
>  printing machines (for which most CYMK TIFF/JPEG files are intended)
>  will produce even other colours.
> 
>  For a decent RGB <-> CMYK conversion (which you simply need, if you
>  want to display a CMYK image on a CRT or LCD monitor), I'd recommend
>  to use ICC profiles. An ICC profile provides a kind of "colour
>  description" for a certain device, like a CRT monitor, an inkjet
>  printer, a scanner or a digital camera. You'll find more information
>  on ICC at http://www.color.org. A very good free implementation of
>  ICC based colour conversions is Littlecms
>  (http://www.littlecms.com). Aside from a library for ICC colour
>  conversions, littlecms also provides programs for RGB<->CMYK
>  conversions of JPEG and TIFF images. The littlecms web site has also
>  many useful links to other ICC resources.
> 
>  Abel
>  _______________________________________________
>  Image-SIG maillist  -  Image-SIG@[...].org
>  http://mail.python.org/mailman/listinfo/image-sig
> 
> 
>  


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