Basic Options

Step Size

“Step” is displacement distance for every filter iteration. A 10 value is necessary to get a one pixel displacement. This value can be negative to invert displacement direction.

Iterations

Iteration is the number of repetitions of effect when applying filter.

On Edges

Because of displacement, a part of pixels are driven over the borders of layer or selection, and, on the opposite side, pixels places are emptying. Four following options allow you to fix this issue:

• Warp (default): What goes out on one side is going into the opposite side.

• Smear: Emptying places are filled with a spreading of the neighbouring image line.

• Black: Emptying places are filled with black color.

• FG Color: Emptying places are filled with the Foreground color of the color area in Toolbox.

Displacement Map

To be listed in this drop-down list, the displacement map, which is a grey-scaled image, must be present on your screen when you call filter and must have the same size as the original image. be

Advanced Options

Dither Size

Once all pixels displaced, this option scatters them randomly, giving grain to the image. The higher this value (0.00-1.00), the thinner the grain.

Figure 11.116.  With a 3.00 dither size:

Rotation Angle

This option sets displacement angle of pixels according to the slope direction of gradient. Previous examples have been created with a vertical gradient and a 90° angle: so, pixels were displaced horizontally and nothing went out of the image borders. Here is an example with a 10° angle and 6 iterations:

Figure 11.117.  With a 10° angle and 6 iterations:

Displacement is made according to a 10° angle against vertical. Pixels going out the lower border on every iteration are going into through the upper border (Wrap option checked), giving a dotted line.

Magnitude map

In addition to displacement map, you can add a Magnitude Map. This map is also a grey-scaled image, with the same size as the source image and which must be present on your screen when you call filter. This map gives more or less strength to filter on some parts of the image, according to the grey levels of this magnitude map. Image areas corresponding to white parts of this map will undergo all the strength of filter. Image areas corresponding to black parts of the map will be spared by filter. Intermediate grey levels will lessen filter action on corresponding areas of the image. Use magnitude map must be checked for that.

Figure 11.118.  Magnitude Map example:

From left to right: original image, displacement map, magnitude map, after applying “Warp” filter. You can see that the black areas of magnitude map prevent filter to take action.