In Photivo several filters rely internally on a luminance mask to restrict the effect of a filter to a certain tonal range. These masks are modelled after the common workflow in Gimp: Get a luminance representation of the image and mask the desired parts.

Parameters:

• MaskType
• Lower Limit (Range: 0 to 1)
• Upper Limit (Range: 0 to 1)
• Softness (Range: -2 to 2)

Behaviour

• All values: It is a full mask, so all parts get the same full intensity. The other three sliders have no impact at this setting.
• Shadows: The darker values get more impact as the brighter ones. By increasing Lower Limit it will get even stronger in the darker areas. By decreasing Upper Limit one can mask out the bright areas of the image.
• Midtones: Only the midtones of the image are selected. Lower Limit to min and Upper Limit to max result in an even effect all over the image (same as all values). By increasing Lower Limit one can mask out the dark areas and by decreasing Upper Limit the bright areas can be masked out.
• Highlights: The effect is stronger in the brighter areas. By increasing Lower Limit the darker areas can be masked out, by decreasing Upper Limit the effect gets even stronger in the brighter areas.

The Softness slider brightens or darkens the layermask, which additionally controls the strength of the effect. The strength of the effect decreases with increasing softness values, which means the softness of the transition areas increases with increasing softness values.