As the colour varies continuously across a vignette, it may change from a lighter to darker hue than the colour on the opposite side of the boundary. This would cause the trap to jump suddenly from one side of the boundary to the other at the point of the transition (as shown in the figure below).
StudioRIP avoids this undesirable effect by creating a sliding trap that shifts gradually, rather than abruptly, from one side of the boundary to the other, as in the figure on the right.
