Re: [GD-DEVEL] RGB to Lab colorspace conversion

The links to the functions that I sent were all written by me (based off of
the math on the Wikipedia articles
http://en.wikipedia.org/wiki/Lab_color_space
http://en.wikipedia.org/wiki/Color_difference and the EasyRGB website
http://www.easyrgb.com/index.php?X=MATH
http://www.easyrgb.com/index.php?X=DELT).

If you are concerned about the GPL license on the code from Google Code, I
would be happy to let you port that code for GD. Please let me know if there
is anything that I can do to help make this happen.

Joe

On Tue, Jan 26, 2010 at 11:42 AM, Pierre Joye <[email protected]> wrote:

> hi,
>
> Color conversions would rock. If you can find implementation under a
> BSD license (or similar but not GPL), we will happy to port them.
>
> Cheers,
>
> On Mon, Jan 25, 2010 at 11:41 PM, Joe Lencioni <[email protected]>
> wrote:
> > First of all, thank you for developing GD. It is an indispensable tool
> for
> > working with images in PHP.
> >
> > I am working on an image resizing and cropping script that attempts to
> > detect which areas of an image are more important when making cropping
> > decisions--essentially asking the computer to determine perceptual color
> > differences. To accomplish this, I convert pixels from the RGB colorspace
> > into Lab colorspace and compare the differences. (
> > http://en.wikipedia.org/wiki/Lab_color_space#Advantages_of_Lab). While I
> can
> > make this happen in PHP, it is slow and uses too much memory. I would
> love
> > to see functions to facilitate this conversion and comparison directly in
> > GD.
> >
> > To convert from RGB to Lab, you first need to convert from RGB to XYZ
> > colorspace and then from XYZ to Lab colorspace. Here are the functions
> that
> > I use for conversion in PHP (which have been derived from the formulas on
> > the EasyRGB website http://www.easyrgb.com/index.php?X=MATH):
> >
> > GD color index to RGB:
> >
> http://code.google.com/p/smart-lencioni-image-resizer/source/browse/trunk/slirimage.class.php?spec=svn59&r=46#755
> > RGB to XYZ:
> >
> http://code.google.com/p/smart-lencioni-image-resizer/source/browse/trunk/slirimage.class.php?spec=svn59&r=46#770
> >
> > XYZ to CIE-L*a*b* (more complex):
> >
> http://code.google.com/p/smart-lencioni-image-resizer/source/browse/trunk/slirimage.class.php?spec=svn59&r=46#825
> > or
> > XYZ to Hunter-Lab (less complex):
> >
> http://code.google.com/p/smart-lencioni-image-resizer/source/browse/trunk/slirimage.class.php?spec=svn59&r=46#806
> >
> > And comparing the colors (more info at
> > http://en.wikipedia.org/wiki/Color_difference):
> >
> > deltaE 2000 (complex):
> >
> http://code.google.com/p/smart-lencioni-image-resizer/source/browse/trunk/slirimage.class.php?spec=svn59&r=46#874
> > or
> > deltaE 76 (simple):
> >
> http://code.google.com/p/smart-lencioni-image-resizer/source/browse/trunk/slirimage.class.php?spec=svn59&r=46#857
> > or
> > deltaE CMC:
> >
> http://code.google.com/p/smart-lencioni-image-resizer/source/browse/trunk/slirimage.class.php?spec=svn59&r=46#967
> >
> > For accuracy purposes, I would prefer to be able to use the more complex
> > equations. However, if they prove to be too slow, it would be nice to
> fall
> > back on the simpler versions.
> >
> > So my question is this: does this kind of functionality make sense to
> > include in GD (I hope so)? If so, will you add it? I am unfamiliar with
> C,
> > otherwise I would submit the code, but hopefully it won't be too much
> work
> > to convert the PHP functions I have provided here.
> >
> > Thanks!
> > Joe
> >
>
>
>
> --
> Pierre
>
> @pierrejoye | http://blog.thepimp.net | http://www.libgd.org
>