Sobel filter

Use the Process > Edge Detection Filters > Sobel... command to highlight the edges of objects.

The dialog box that is opened when you use an image processing operation is made up in the same way for every operation. Click here to switch to a description of this dialog box.

Exactly what happens?

The Sobel filter is a genuine edge-detector and does not react so sensitively to noise effects. This is because differentiation is conducted using the image lines and columns beyond the next-immediate ones. Thus - any interference in image lines and columns directly next to your central pixel cannot influence the results.

The Sobel filter is a non-linear method for highlighting edges. This filter is comprised of a set of derivative filters. Intensity modulations that are either horizontal or vertical will be especially enhanced. The Sobel filter generally yields the amount of the difference and the direction of the most significant change.

Filter matrix

The filter uses two matrixes, by means of which the values a and b are calculated. The resulting intensity value is: √ (a²+b²)

	a			b
-1	-2	-1	-1	0	+1
0	0	0	-2	0	+2
+1	+2	+1	-1	0	+1

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