How I can do edge detection to almost white picture where are black lines/edges?

How I can do edge detection to almost white picture where are black lines/edges? So I want to do edge detection to black edges.

[Jan]

I've closed this question, because the body is empty. It is re-opened automatically, if you add the required details in the currently empty body of the question.

Answer 1

[ChristianW]

This demo might answer your question: http://www.mathworks.de/products/image/examples.html?file=/products/demos/shipping/images/ipexcell.html

[Teemu]

The demo was good, thanks!