Spiral transform : keeping the edges in place? as twirl / swirl effect

[pierrelabreche]

Is there a way to create a spiral variant (twirl), whereby central pixels along the image frame are un-twisted ?
In other words, the spiral effect is neutralized on the midpoint along the image sides.

For an example see Photoshop's twirl dialog box :
( as presented in from https://www.photoshopessentials.com/pho ... rt-effect/

[jsachs]

You can do this with the Displace transformation by creating a mask for the rotation angle the starts out white in the center and fades to black at the edges.

This Spiral transformation, if the radius stays in-bounds in the image, will leave the edges untwisted, but the effect is abrupt.

[pierrelabreche]

Very interesting use of the mask.

Could the displace transform accept other displacements such as spiral and its variants ( solid, linear, hyperbolic, logarithmic ) ?

[jsachs]

If the maximum amount of rotation in Displace were not limited, you could use a mask to simulate other types of spirals by playing with the rate of falloff from the center to the edge, but I don't think this is a good direction to try to go in since this would be hard to control.