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

hi,

Ah, you are the author of this code? If yes and if you agree to
relicense it to BSD for GD (the port), then everything is fine :). If
you are not the author, then we have to implement it from scratch
based on the specs.

Cheers,

On Tue, Jan 26, 2010 at 6:59 PM, Joe Lencioni <[email protected]> wrote:
> 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
>
>



-- 
Pierre

@pierrejoye | http://blog.thepimp.net | http://www.libgd.org