# Confusion related to an edge detection filter

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It's mentioned that this detector detects the edges in the east direction. I am confused how come the direction is east. It should have been north isn't it

It should detect something like | rather than - isn't it

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Yes, that mask detects edges oriented "|" rather than "—". By "edge in the east direction" they probably meant an edge whose normal points east (or west, for that matter). –  Rahul Sep 15 '12 at 0:42
I think you compute something like a dot product of this placed on a 3x3 part of your image. To me, this seems like a derivative in the east direction, so the edge is actually going north-south. –  Tunococ Sep 15 '12 at 0:49