Video editing objects from black and white to colour 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...
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.