4.18. Gira i contrau

4.18. Gira i contrau
	4. Filtres Distorsions

4.18.1. Overview

Figura 17.84. Example for the Whirl and Pinch filter

Original image

Filter applied

“Whirl and Pinch” distorts your image in a concentric way.

“Whirl” (applying a non-zero Whirl angle) distorts the image much like the little whirlpool that appears when you empty your bath.

“Pinch”, with a nil rotation, can be compared to applying your image to a soft rubber surface and squeezing the edges or corners. If the Pinch amount slider is set to a negative value, it will look as if someone tried to push a round object up toward you from behind the rubber skin. If the Pinch amount is set to a positive value, it looks like someone is dragging or sucking on the surface from behind, and away from you.

	Suggeriment
	The “pinch” effect can sometimes be used to compensate for image distortion produced by telephoto or fish-eye lenses (“barrel distortion”).

Figura 17.85. Illustration

Original

Whirled

Pinched

4.18.2. Activating the filter

You can find this filter through Filters → Distorts → Whirl and Pinch…

4.18.3. Parameter Settings

Figura 17.86. “Whirl and Pinch” filter options

Previsualitza: Changes to parameters are immediately displayed into the Preview. The whirlpool is focused around the center of the current layer or selection.
Angle de gir de cada volta: Clockwise or counter clockwise (-360 to +360). Controls how many degrees the affected part of the image is rotated.
Pinch amount: Whirlpool depth(-1 to +1). Determines how strongly the affected part of the image is pinched.
Radi: Whirlpool width (0.0-2.0). Determines how much of the image is affected by the distortion. If you set Radius to 2, the entire image will be affected. If you set Radius to 1, half the image will be affected. If Radius is set to 0, nothing will be affected (think of it as the radius in a circle with 0 in the center and 1 halfway out).