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Best practice: Compositing

Compositing 3D objects into a photo or film/ video footage is a common task in post-production. There are a number of ways to do it effectively, such as using image-based lighting and radiosity techniques, which are all fairly common in today's 3D applications. However, making a custom HDRI image for your lighting scheme actually requires a great deal of fiddling about to capture the lighting and environment correctly during your initial shoot.

Before HDRI you could still composite 3D objects into footage pretty convincingly, it just needed a bit of skill and experience. In this example we'll show you how you can use your lights to recreate the illumination by hand. There's no voodoo at work here, just a little common sense and patience. Just about any 3D program that you work with will have the tools to enable you to do this, so there's no financial outlay involved.

Often you may only have the background image to work from but, if at all possible, try to obtain a second reference image of the scene that contains a roughly spherical diffuse white object (a fist-sized ball of white cotton wool works well, or even a white coffee cup or bowl). You can use this object to take colour samples so that you can gauge the colour and depth of the light that's coming into the scene at different angles. This can help to eliminate some of the annoying guesswork from the task. Though as you'll see from this tutorial it's not always necessary.

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