How does digital chroma key composting work?

Approximately 12 years ago, a photographer took a photo of me that was superimposed on a background scene. It was not done digitally. I believe it was done using slides. The photographer showed me various backgrounds and photos he had taken in his studio that appeared to me to have been taken at some other location.

I have several questions.

Is this a common practice and how do I do this?

Is everything done in Photoshop nowdays?

Is there a source for stock backgrounds availabe for purchase, or do photographers take their own background images.

-Jay

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2 thoughts on “How does digital chroma key composting work?

  1. StudioLighting.netStudioLighting.net

    Jay,

    Glad you enjoy the show!

    The process is called chroma-key and it is fairly common especially in video studios. It can certainly be done for still photography and offers some exciting potential in todays digital environment. I am not familiar with how this was done before digital processing became popular, but I think you are right about most digital composting happening in PhotoShop now.

    As for technique, you simply photograph your subject in front of a special blue or green background that is well lit. Try to avoid the reflected colored light spilling onto the outline of your subject as this is hard to clean up. A tip we received from Joel Svendsen in our latest episode of LightSource is to backlight your subject with a CTO filter to cancel out the color of the screen that hits your subjects hair and shoulders. He also said it is useful to light the background with filtered light to get a stronger color reflection – though he explained it better than me!

    Once the image is captured, you can use photoshop to select the background by color and remove it. Placing them on new backgrounds is as simple as importing another image as a new layer.

    The images can be taken by the photographer, or purchased at any stock photography outlet. If you take them yourself, be careful that the lighting matches (intensity, color, direction) the studio shot in order to have a believable final image.

    There are some professional chroma key software packages that can help with the keying process. One application is ULTRA 2 by Serious Magic.

    There are also some nice collapsable chroma backgrounds available by Westcott.

    Make sure you listen to Episode 010 of LightSource for more tips on chroma key lighting.

    -Bill

  2. Chuck

    Prior to digital work, it was usually done with a system referred to as “environment projection”. Essentially, the camera was pointed at the floor while a projector with the background slide on the floor was pointed directly into the lens. Between the two, a piece of silvered glass angled towards the subject who was standing in front of a black background. The studio flash was calibrated to generate enough light off the subject to overpower the projector — but where the light fell on the black background, the projector image hit the film. No special processing was necessary — just careful calibration of the lighting.

    It was very effective and actually very simple technology. Computers have just made it easier — especially since so much photography has a digital goal anyway!


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