Spiral

This transformation warps a circular region of an image by twisting it into a spiral.

Several different types of spirals are supported. When you start up the Spiral transformation, it displays an overlay over the input image window to show you the circular region of the image that will be twisted. A control point is displayed at the center of the circle. Clicking and dragging this point repositions the circular region. The radius of the circle is adjusted with the Radius slider in the Spiral dialog box.

Type

Linear -- the twist angle increases proportionally to the radius.

Logarithmic --the twist angle increases as the logarithm of the radius.

Hyperbolic --the twist angle increases as the reciprocal of the radius -- this type of spiral is very tightly wound near the center.

Solid -- the entire interior of the circular region to be rotated as a unit.

Radius

The radius slider lets you select the size of the region to be twisted. As you vary the radius, the circle displayed over the input image changes size to show you what part of the input image will be affected.

Spin

The spin slider lets you select the amount of twist to be applied to the input image. The lower the value you select, the less the input image will be distorted. Negative values twist in the opposite direction.

Antialias

Certain spiral settings result in images that have slightly jagged edges. For example, when computing a solid spiral, the boundary between the rotated and unrotated portions of the image may be a little rough. Or, the center region of a hyperbolic spiral may also degrade into individual pixels. To counter this phenomenon called aliasing, you can increase the antialias setting. Doing so will reduce the aliasing artifacts at the expense of increased time to compute the transformation.