This filter can be used to keep RGB pixel values inside a specific range. Most of the time this filter seems to work best if you have both the low and high limit between 0 and 1. However, you can get some cool effects when selecting a high close to 0 and and low greater than 1.
« Presets » are a common feature for several Colors commands. You can find its description in Section 8.1.1, « Fonctions communes aux couleurs ».
When checked, low pixel values will be clipped.
Pixel values lower than this limit will be set to it.
When checked, high pixel values will be clipped.
Pixel values higher than this limit will be set to it.
These are common features described in Section 8.1.1, « Fonctions communes aux couleurs ».