From Synfig Studio :: Documentation
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About Clamp Layer
Clamp layer is used to limit colours to a certain range of component values.
The R, G, B and A (alpha) components of each pixel are forced to lie within the range Floor...Ceiling.
If "Clamp Ceiling" is off, then only the Floor is considered.
If "Invert Negative" is on, then a pixel with a value of A less than Floor is first negated (-R, -G, -B, -A) and then something funny happens to raise all the components to at least Floor. Any ideas what this is for?
Parameters of Clamp Layer
The parameters of the Clamp Layers are: