Well I have no idea if this has ever been considered but:

Would it be a nice idea to add a few settings to the camera? The settings I am thinking of are sensitivity sliders for color for instance. Say similar to the colorband sliders. Where you can set a sensitivity and perhaps a threshold for each of the 3 colours. That way you could easily do lots of effects without needing a lot of other post production software.

We have quite a few options where lights and materials are concerned, but with the camera itself we can do very little.

The kind of effect you describe you probably be more suited for a sequence plugin.

Martin
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