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Bischofftep
09-25-2003, 09:11 PM
Hello!

Playing around with the demo for 2.1, and very interested in possibly picking up this package especially now that they've announced Combustion 3 will be available for the Mac.

One question I have involves what essentially is a "clean plate" against live footage whose lighting varies.

What I've got so far:
* Track the cleanplate to a feature on the background so that it follows the camera's motion.
* Mask the cleanplate so that the areas that need "cleaned" are the ones that show through.

So far this works beautifully. Now, when the lighting (an ourdoor scene with clouds moving across the sun... how inconsiderate...) changes in the live footage, the color of the cleanplate no longer matches up with the color of the live footage.

Is there a way to automate the color correction of the cleanplate so that it follows something on another layer?

Ideally, the "offset" feature of Discreet Basic CC could be used: the "source" point is identified on the live footage in the same frame as the cleanplate was taken from at a pixel that appears in both the original footage AND the cleanplate. The "target" pixel is this same pixel on the cleanplate.

If that would work on a frame-by-frame basis it would color correct the cleanplate on-the-fly to match the variations in the rest of the live footage. For relatively small areas of footage this works really well... but keyframing the CC isn't doing the trick. I need frame-by-frame control!

Is there a way to do this?

And... if I'm approaching the concept of removing an object from a scene all WRONG, any pointers would be very appreciated.

Thanks!

arvid
09-26-2003, 09:07 AM
I did something similar, a talent shot in front of a greenscreen traveling fast in a cg tunnel with lights in the roof, meaning the foreground would have to be "lit" as it passes under the light and become darker when it exits the light, every 5 frames or so :)
I made a small mask to sample a part of the wall where I wanted to take the brightness from then centered that little lightdot and scaled it way up to cover the entire foreground, making a big general colour representing the brightness.
I suppose that image can be used in different ways but I used the inverted RGB as a matte to constrain the brightness (I guess, as a selection in combustion-terms), after setting the drakest point in the brightness setting.
That means that when the little sample on the wall gets lighter, the brightness-effect has less influence (since its inverted) thus making the foreground lit, all in perfect sync with the background :)

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