[Gimp-developer] Automatic white balance

[Stephane Chauveau]

Øyvind Kolås wrote:
> On Nov 27, 2007 7:00 PM, Stephane Chauveau
> <stephane at chauveau-central.net> wrote:
>   
>> Øyvind Kolås wrote:
>>     
>>> You could start out by studying the following paper, as well as it's references:
>>> http://www.ivl.disco.unimib.it/papers2003/WB%20Combining%20%20EI%206502-12.pdf
>>>
>>> /Øyvind K.
>>>
>>>       
>> Nice article. The following Wikipedia pages does not describe so many
>> methods but are probably easier to start with:
>>
>>  http://en.wikipedia.org/wiki/White_balance
>>  http://en.wikipedia.org/wiki/Color_temperature
>>
>> The following article is even less technical but is also a nice read and
>> it explains the most common issues with automatic WB.
>>
>>  http://www.cambridgeincolour.com/tutorials/white-balance.htm
>>
>> Anyways, a plug-in providing several WB methods would be cool but, in
>> most cases, I believe that it would be even better to extend the Color
>> Balance tool with the ability to manually pick the grey point in the
>> image. The easiest way to implement that feature could be to add a 'Set
>> White Point' button to the Color Picker tool.
>>     
>
> This functionality exists in the levels tool already.
>
>   
Nice! I never noticed that the grey point picker in the level tool could 
be used to adjust the  WB.  It is  unfortunately limited to the mid-tones.

The behavior I have in mind is quite different and is more like the one 
found in most cameras and described in the paper you mentionned (the Von 
Kries hypothesis): figure out a grey point to compute a set of 3 
coefficients (for red,green and blue) and multiply each channel by its 
respective coefficient (with clipping). See for example how WB can be 
done in UFraw by selecting a grey area with the mouse.
> Personally I'd prefer a gui similar to:
>
> http://pippin.gimp.org/plug-ins/color_correct/
>
> for a combined levels (on luminance) and white point/gray point/black
> point offset. Since I don't find it entirely natural to modify the
> white point using levels.
>
>   
Me neither. The grey/white point in white balance (the illuminant tint) 
and the grey point in levels (the average brightness) are very different 
concepts.
> /Øyvind K. (Doing full quote and replying to the list since the
> message I reply to didn't seem
> to be sent to the list.)
>