USING ALPHA CHANNELS

An Alpha channel is a black and white image that tells the program which areas to make invisible. For Carrara- black is invisible and white is visible. In this example, I filmed a person in front of a blue screen and made a duplicate film where the blue was made black and everything else was made white. This black and white film was imported into the alpha channel. A second way of doing this is to import the film into a compositing program like After Effects which can make the blue invisible (a process called KEYING). After Effects can thenadd an alpha channel to the film and Carrara automatically recognizes the alpha. I put the footage into the glow channel (not color) because the footage is already lit and you probably don't want the lights affecting your image. Make sure the color channel is NONE or BLACK

A single flat polygon is all you need

Put the color image or film in the color or glow channel. If it contains an alpha channel, Carrara automatically uses it...

...otherwise put your greyscale map into ALPHA. Check Light throgh Transparency in the render room.

Add a POINT AT modifier to the plane polygon so it always points at the camera.

To create a KEY or MATTE, use a background color that is not found in the foreground like blue or green. The poor-man's way is to use a black background and light the subject brightly.

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Carrara can also render images and movies with alpha channels so the object is separated from the background and imported into Photoshop etc.

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