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I was reading this article related to edge detection and here is a edge detection mask

-1 0 1
-1 0 1
-1 0 1

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

This mask is one part of Prewitt operator. Please have a look at :

It detects vertical edges, while its transpose detects the horizontal ones. Prewitt operator is the aplication of both masks, one after the other.

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