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
