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" <[EMAIL PROTECTED]> To: "Cesare Leonardi" <[EMAIL PROTECTED]> Cc: <image-sig@python.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@python.org > http://mail.python.org/mailman/listinfo/image-sig > > > _______________________________________________ Image-SIG maillist - Image-SIG@python.org http://mail.python.org/mailman/listinfo/image-sig
