User Guide

GNU Image Manipulation Program
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Smoothing parameters Radius 1 and Radius 2 are the blurring radii for the two Gaussian blurs. The only constraints on them
is that they cannot be equal, or else the result will be a blank image. If you want to produce something that looks like a
sketch, in most cases setting Radius 2 smaller than Radius 1 will give better results.
Normalize Checking this box causes the brightness range in the result to be stretched as much as possible, increasing contrast.
Note that in the preview, only the part of the image that is shown is taken into account, so with Normalize checked the
preview is not completely accurate. (It is accurate except in terms of global contrast, though.)
Invert Checking this box inverts the result, so that you see dark edges on a white background, giving something that looks more
like a drawing.
15.5.3 Edge
15.5.3.1 Overview
You can find this filter through Filters → Edge Detect → Edge....
Figure 15.80: Applying example for the Edge filter
(a) Original image (b) After applying the filter (Sobel option)
Figure 15.81: Applying examples for the Edge filter
(a) After applying the filter (Prewitt option) (b) After applying the filter (Gradient option)