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For school we came up with a cool concept, the video starts in black and white and when a person in the video touches an object it turns to colour.

Could you guys help us out here? Do you have any tutorials for us? Which programs do we have to use (the price of the software is not a problem).

Thanks!

PS.

I now understand that rotoscoping can be used for this. But how bout a gradual change from black and white to colour if a building has been touched for example? For it to change in one frame will look kinda terrible...

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  • You could keyframe the roto, so that it spreads over the building through the course of several frames.
    – Jason Conrad
    Commented Mar 14, 2013 at 0:42
  • @JasonConrad, how could I do do this if the camera is moving? I believe I can use a program such as Boujou for this, I just dont know exactly what to do.
    – Ilya Karnaukhov
    Commented Mar 18, 2013 at 19:14
  • Boujou is for motion tracking and match moving, which would work if your characters are interacting with CG elements (buildings built in maya, max, c4d, etc), but if you're talking about a VFX shot where you want color to spread over real world buildings, you probably need to take a more frame-by-frame, hand-painted approach. That's what rotoscoping is all about. Programs like mocha, bundled with AE, take a lot of the agony out of this process. It doesn't matter if the camera is moving.
    – Jason Conrad
    Commented Mar 19, 2013 at 14:04

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This will probably require a technique called rotoscoping, which involves painting a mask on each frame. You would need to have two layers of video, one which is desaturated (to make the image black and white) and one which is full color. You would then need to make a mask (a layer which effectively makes a hole in the black and white layer so that the color layer can be seen). Since the mask may change based on camera movement and actors moving around the scene, you have to update the mask periodically (possibly every frame).

You can simplify the process quite a bit if the objects are stationary in the scene and the camera is stationary on a tripod. You could also try using object tracking to maintain the placement of the mask roughly, but to get a satisfactory result, you will probably still need some rotoscoping.

After Effects can accomplish what you are looking for. Any tutorials on rotoscoping and masking in AE would work to demonstrate the finer points of what tools to use to accomplish it.

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