User Guide

GNU Image Manipulation Program
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You can find this filter through Filters → Colors → Value Invert
This filter inverts Value (luminosity) of the active layer or selection. Hue and Saturation will not be affected, although the
color will sometimes be slightly different because of round-off error. If you want to invert Hue and Saturation also, use Layers
→ Colors → Invert.
Note that hue and saturation can be distorted quite a bit when applying twice this filter for colors with a high luminosity ( for
instance, HSV 102,100%, 98%, a bright green, gives HSV 96, 100%, 2% after a first application of the filter , and 96, 100%,
98% after a second application) . Thus, you should not expect to be able to apply this filter twice in a row and get back the image
you started with.
Figure 15.66: Example of using this filter twice
(a) Original image (b) First application of the filter (c) Second application: the image is not exactly
the same as the original one.
15.4 Noise filters
15.4.1 Introduction
Noise filters add noise to the active layer or to the selection. To remove small defects from an image, see the Despeckle and
Selective Gaussian Blur filters.
15.4.2 Hurl
15.4.2.1 Overview
You can find this filter through Filters → Noise → Hurl.
The Hurl filter changes each affected pixel to a random color, so it produces real random noise. All color channels, including an
alpha channel (if it is present) are randomized. All possible values are assigned with the same probability. The original values
are not taken into account. All or only some pixels in an active layer or selection are affected, the percentage of affected pixels is
determined by the Randomization (%) option.