The IBK3D Keyer has a feature that can compensate for a non-pure green- or blue screen. Non-pure means that the backdrop (screen) color is not 100% green or 100% blue. The consequence is that the spill suppression algorithms will produce a slightly colorized result, leading to unnatural-looking edges.

Below is an example where the green screen looks very green, but the color is not pure green:

The RGB values of the image above are 0, 241, and 74. A more optimal pure green screen would have RGB values of 0, 241, and 0. The screen color is a bit blue, although this is hard to see using your eyes. In Composer, you can use the Color Picker tool to study the color of your backdrop (screen).

Using the Spill Suppression algorithm without Screen Color Compensation would produce a result similar to the image below:

As you can see, the spill-suppressed result is not neutral (or gray). The RGB values are 1, 38, and 75. This is a blue-ish color, and this will produce challenges when trying to create a perfect chroma key result. The edges of the image and the hair will become slightly blue.

The optimal RGB values are 0, 0, and 0. However, this is rarely possible in real life due to irregularities in the green screen and the complexity of the despill method. However, the result can be improved using the new Screen Color Compensation feature. 

Below is the same image, but in this case, we have activated the Screen Color Compensation feature:

As you can see, the spill-suppressed result is better. It is not perfect, but it is a significant improvement. The RGB values are 1, 7, and 14, a color close to neutral (or gray).

The final result depends on how well the spill suppression algorithm performs. Below is an example without Screen Color Compensation:

Activating the Screen color Compensation produces a more natural image where the edges blend more naturally with the background:

Activating the Screen Color Compensation feature will render a slightly higher load on your server. It is recommended only to activate the feature if your backdrop has a non-pure green or blue color.

Compensation Boost

To increase the amount of screen color correction, you can use the Compensation Boost setting. Increasing the boost will increase the compensation. Be careful not to overuse the Boost setting - it may cause your edges to become too dark.