Quote:
Originally Posted by rmuhlack
Using the approach suggested above, if using OSC could you shoot two sets of subs: one set without the filter that is used for RGB, and a second set of subs with the filter on that is then used just to produce the L signal. Then combine the L with the RGB as you would with a mono camera.
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Spot on!
To remove bias, yes, pixel math - create a model of the bias (ex. light pollution) and subtract that model from the rest of the image. For the Photoshop afficionados it's a simple matter of subtracting one layer (the bias) from the other (the light polluted image). You must do this while the image is still linear (e.g. unstretched) though, otherwise your colors will still be off.
The trick is of course to model the bias faithfully, but if it's really even across the whole image you could just use a dropper and sample a pixel (or bunch of pixels) that you're absolutely of that they are background pixels (e.g. pixels that should become completely neutral black once the model has been subtracted). Then use the RGB value that you found with the dropper and fill the whole layer with that RGB value. It's quick & dirty but could work reasonably well.
For the more serious work there is ofcourse GradientXTerminator (PS), DBE/ABE (PixInsight), Wipe (StarTools), etc.