Chroma Key

Chroma Key is a process that is used in still and video productions that allow a subject to look like they are in a different location. One would look at the following image and assume the man is in front of a window.

In reality the man was shot in a studio and later dropped into a background. This is often called a green screen (blue is used also) and it has been around for some time. Did you ever wonder how the weatherman appears to be standing in front of the weather map not knowing where to point or missing the thunderstorm when they do point at something. That is chroma key. This process starts out with a photo of a subject in front of a green screen. This requires specific lighting because you want a good separation between the screen and the subject. If this is no accomplished, the green will bleed to the subject. Especially in women's hair.

With a good consistent background you can just use the color range command in the Select menu. If there is some variance in the background holding the shift key while clicking the differing gradations of the background will select the whole color range. I do this on a copy of the original image so I can just delete the selection after I have expanded the selection by one pixel (Select-Modify-Expand).

Once the subject is isolated, drop the background in and its onto blending. The image in this example was done somewhat quickly from stock so the lighting is off just a bid but you get the idea. Below is the layer stack from this project.

Two adjustment layers were added to the subject to better blend him with he background. Both are clipping masks as designated by the down arrows to the left of the layer. The first was a levels adjustment to set the light quality as close as I could given the lighting pattern. The second was a cooling filter to match the background.

That's Chroma key.

Take care all... Doug