User Guide

GNU Image Manipulation Program
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Dither Size Once all pixels displaced, this option scatters them randomly, giving grain to the image. The higher this value
(0.00-100.00), the thinner the grain.
Figure 15.223: 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 15.224: 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 15.225: 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.
MORE ADVANCED OPTIONS
The Gradient Map The gradient map is also a grayscaled map. Here, the displacement of pixels depends on the direction
of grayscale transitions. The Gradient scale option lets you set how much the grayscale variations will influence the
displacement of pixels. On every iteration, the filter works of the whole image, not only on the red object: this explains
burredness.