Keying

Keying, also known as chroma keying or color keying, is the process of converting a specific range of colors into the alpha channel, to show the background footage when layered. The following screenshot shows an example of this concept:

Value and luminance

A clear understanding of the differences between value and luminance is very essential in compositing since the human eye is more sensitive to luminance than to colors. It turns out to be even more crucial while keying, since everything in keying is dependent on how you start the process, with respect to a specific channel in a specific color space. To explain this in detail, the following screenshot will be used, which contains different tones with at least one of the RGB components having a value of 1:

The desaturation of an image will result in displaying the value of the image. The value displays the maximum value in between the RGB components. Since the input image has the value as 1 in any one of the RGB channels, the result...