“Presets” are a common feature for several Colors commands. You can find its description in Odjeljak 8.1.1, “Colors Common Features”.

Component to extract. Default is RGB Red: all layer pixels that have the red component in their color will be extracted to create gray pixels; gray pixel value is that of the red channel (e.g a 153;70;17 RGB pixel will give a 153;153;153 gray pixel).

Invert the extracted component.

Use linear input instead of gamma corrected.

These are common features described in Odjeljak 8.1.1, “Colors Common Features”.