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What is the difference between edge detection and contour detection?

Apparently both techniques are used to detect boundaries of close shapes(whether oval shape or r rectangular shape)

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Contour is the edge closing an object. So you can think as higher level of edge detection.

So if an edge define an object it becomes a contour.

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  • $\begingroup$ Consider a rectangle, it will have 4 edges(each edge across one side) and one contour made up of 4 edges? Am i right? $\endgroup$
    – Man
    Apr 21 '20 at 11:45
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    $\begingroup$ Yep. This is the idea. $\endgroup$
    – Royi
    Apr 21 '20 at 11:46
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I would consider the notion of edge, with respect to that of contour, in the same relation as words to a sentence. An edge is a distinctive element of an image (a color change, a border cut, a shadow, an occlusion). Here, from top to bottom: surface normal, depeth, illumination, shadow.

Types of edges

But sometimes, this does not fully takes advantage of the whole concept of objects, which requires higher-order methods, semantics, viewpoints, etc. Look at the following 3D object, which is relatively homogeneous and isolated edges:

3D object, shadows and edges

While edges can be detected by relatively local tools (derivatives, Laplacien, thresholding, wavelets, Gabor functions etc.), contours often require more involved and global techniques: active contours, geodesic active gradients, etc.

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