[Image-SIG] RGB conversion to CMKY gives strange results

[kevin at cazabon.com]

FYI, you can also do color space conversions using ICC profiles - in the end
the best method, assuming you have good profiles for the specific
application.  I wrote an ICC module for PIL called pyCMS.  See:

http://www.cazabon.com/pyCMS/

Fredrik - there's still a standing offer if you're interested in
incorporating the usm / gausian blur, or even pyCMS into the standard
library.  However it sounds like you're hands are full these days too!  (My
little one has limited my spare time significantly, otherwise I'd just send
you diffs)

Kevin.
----- Original Message ----- 
From: "Ray Pasco" <pascor at hotpop.com>
To: "image-sig PIL" <image-sig at python.org>
Sent: Thursday, March 10, 2005 5:30 AM
Subject: [Image-SIG] RGB conversion to CMKY gives strange results


> I'm using the im.convert() from RGB to CMYK and am getting very strange
> results.
> First, the K value is stuck at zero no matter what the RGB values are.
> Next, the C, M and Y values are integers and not in the value range 0.0
> - 1.0.
> I have no idea what they mean. They seem to bear no relationship at all
> to the
> proper CMYK values.
>
> I coded an RGB to CMY to CMYK algorithm derived from the formulas
> found at http://www.easyrgb.com/math.php?MATH=M2#text2 , which
> seem to be correct.
>
> Is im.convert ('CMYK') broken ? I'd like to use it since this is the only
> colorspace conversion available in PIL.
>
> Is there any particular reason why conversions to HSV and/or HSL don't
> exist ?
> It would really useful to work with brightness or luminosity directly.
>
> (1.1.5b1 on XP)
>
>
> _______________________________________________
> Image-SIG maillist  -  Image-SIG at python.org
> http://mail.python.org/mailman/listinfo/image-sig
>
>
>