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white,grey and black point plugin

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I've got a plugin that does something similar to your idea.

The effect dialog gives a 'thumbnail' of the current layer; if you click the mouse on a point within the thumbnail, then the effect will try to make that point a gray color...

You can get it here White Balance Prototype Plugin.

IMPORTANT: It's still very much a prototype...

As always, I'd be interested to get some feedback.


Ed, this looks nice and your plugin gives fairly good results, except for areas that include channel clipping.

For example if there is severe blue shift with areas having B=255 then blue is not reduced there.

You will understand what I mean when you try to correct this image here (I have kept it as a good sample of really bad WB).

Take the "gray reading" from the sidewalk surface and whole picture becomes nicely balanced except restaurant wall, because it has clipped blue.

I agree a logic that clipped white should not be shifted, but I think that in case of just a single clipped channel the pixel needs to be adjusted.

Would it be possible to implement WB adjustment so that ONLY pixels having EVERY channel value over 250 (clipped white basically) will not be shifted?

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Yes, I used a 'quick-and-dirty' method as the plug-in I posted was just a proof-of-concept. Real WB correction is considerably more complex :(

I have since implemented a far more complex and perceptualy realistic method known as the Linear Bradford Chromatic Adaptation.

I am still testing this, and it's not yet ready for public release (lots of tuning still required), but preliminary results are quite promising; It's always nice when theoretical methods 'play nice' in real life :)

As an example, see my previous post or have a look here for a quick attempt at correcting your example...



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