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

Posted: October 14th, 2022, 1:03 pm
by 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/

Image

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

Posted: October 14th, 2022, 1:31 pm
by 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.

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

Posted: October 15th, 2022, 8:36 pm
by pierrelabreche
Very interesting use of the mask.

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

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

Posted: October 15th, 2022, 9:10 pm
by 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.