If the chromakey-matting result has flaws, you can use the following parameters to refine the result:

Feather Brush
Adds individual pixels to the mask and ensures a softer transition
from the foreground to the background.

Optimize Edge
Optimizes the mask around the edges of the cropped object.

Reduce Reflected Color
Sometimes, the background reflects its colors into the foreground. This may happen when a person wears white clothes and stands in front of a blue background, which can result in the clothing being semi-transparent. With this option it is possible to reduce this effect.

But now to the practice: Let us take, as an example, the following picture, which shows a landscape with a blue sky, but crossed by some white-grey clouds. From this image, you would like to remove the entire sky including clouds. The different functions of the chromakey-matting menu will be gone through step by step with the help of this picture and, finally, it will be explained how the clouds can be removed

If you apply chromakey-matting to this image by clicking on an area of the blue sky with the pipette-tool as described in the Quick Start chapter, the following result will be shown: The blue areas of the sky were successfully removed, but the clouds were not. These still shine through because they are not blue, but white-grey.

Sensitivity

In the sensitivity-bar, you can increase or decrease the sensitivity of the selected color tone. If you move the left slider in the following example further to the left, the color-range that is displayed transparently expands by the displayed hue-range. To remove the clouds from the image, it might be helpful to move the left slider to the left, as even brighter blue-tones will then become transparent in the image. Then click "Apply" to see the result. With closer examination, this procedure seems to have yielded slight improvements: