How should I shoot a stop-motion subject so the background can be replaced automatically in post?

Question

I’m shooting a stop-motion sequence of a small subject (a banana peel) on a Canon 550D with an 18–55mm lens. I need to replace the background later with a separately animated background, so I want the subject to be easy to isolate automatically across many frames.

My setup is limited: the camera can be about 1.5 m from the subject, the subject is about 0.5 m from the wall, and I only have continuous household lighting. I also have a black cardboard backdrop, but I don’t have a safely syncable flash setup.

What background and lighting approach will make automatic background removal easiest while keeping edge quality usable over many frames?

user2481 · Accepted Answer

Here are all the ways I know of for removing the background (in order of my preference):

White Background

This is done by using a white-ish background and lighting the background about 3 stops brighter than the subjects (exact lighting depending on your camera).

There's no way you can do this with household lights but a flash aimed at the wall behind the subject does this easily, you can do it by shooting your subject with a very slow shutter speed and using your flash's test button or you can get a $40 flash from ebay (plus about $10 for adapters and cables to sync it off-camera).

Note: you will want to get the subject as far from the background as possible to minimize light bouncing from the background hitting the subject.
Chroma-key

Use a solid color background (most commonly green), make sure the background is lighted evenly and that there are no shadows falling on the background.

You can sort of do it with household lights but here it is even more important to not have light from the background hitting the subject (because it will cause a green color cast) so you will need some distance between the background and subject.
Black background

This is done by simply placing the lights very close to the subject and letting the light falloff turn the background black, the more powerful the light the easier it is to get a black background.

Here distance to background is also important but you can manage without it if the light is powerful and very close (but a powerful light very close will create very dramatic hard light - so if you want even soft lighting this is not for you).
Masking in software

If you just carefully paint the mark for each photo you don't care what the original background is - and you don't need any special lights, however, this is obviously very tedious.

You can make an almost-white or almost-black background, use automatic selection and then just refine the mask to save some time.

Whatever you do all of those will confuse the camera's auto mode, don't forget to meter for the subject and use manual mode and manual white balance - and to take test shots and watch them on the computer before starting with the stop motion animation.

How should I shoot a stop-motion subject so the background can be replaced automatically in post?

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