Find array of edges with imageJ

Question

I have already found edges of an image thanks to imageJ library.

Now, I'd like to get an array which would contain these edges.

There is a topic about it here but i couldn't comment and there wasn't the answer: Find Edges with ImageJ Programmatically

Tactile

What will you do with the array of edges? – Bezel

My goal is listing these (horizontal) edges. Example: consider an image where I have found edges (with methods of ij you used in your post). If a line appears as an edge, I would like to list it: it would be a segment with a starting point and an end point. Do you understand what I mean? – Tactile

Yes. With ImageJ you can only get edge-detected version of the image, not the edges, as I know. First, get the edge-detected version of the image. Non-edge pixels will be black, edge pixels will be different. You need to find start and end points of these by yourself. – Bezel

I know but it seemed you did it in your post, not finding precisely start and end points, but array of edges. Thanks btw – Tactile

The title of my question mislead you, I see. I only found the edge-detected image. Sorry for that. – Bezel

Answer 1

As documented in §29.3 Find Edges, the command uses the Sobel operator. Each point of the final image is the magnitude of the gradient of the horizontal and vertical convolutions. A copy of the whole array is returned by the get*Array() methods of the chosen ImageProcessor; the individual elements of the array can be accessed using the various get*() methods.

Addendum: You say, "My aim is to get the edges. My problem is not getting each pixel value."

Edge detection is not trivial; it is typically a multi-stage process. The array of magnitudes is merely the initial result of applying the first-order Sobel operator. The next stages in the pipeline, e.g. thresholding, linking, thinning, depend on your goal.

Tace

True, but my aim is to get the edges. My problem is not getting each pixel value. Ismet Alkan user seems to hava managed this operation, but I don't know how to contact him and I can't comment his post. – Tactile

I've elaborated above; please edit your question to clarify what result you expect. – Tace

My goal is: find connex component. Each major edge would be a connex component which could be referenced. – Tactile

@Archos007: I don't understand connex component. Please edit your question to include a link and for others to see your clarification in the active queue. – Tace

In my first post, there is a link. And my goal is about what users talk in the last posts. One of them says he managed to find edge-found array, but he doesn't explain how. And I can't comment because I've just joined the site. – Tactile

Sorry, I don't think you'll get a different answer, but editing your question is a way to find out. – Tace

Answer 2

Yes, I know this is old, but this needs an answer. Using imageJ programatically

 float edgePixels[][];
 ImagePlus imp = null;
 Opener op = new Opener();
 imp =  op.openImage("lib/EP07-J.jpg");
 ImageProcessor improc = imp.getProcessor().duplicate();

 improc.medianFilter();
 improc.findEdges();
 edgePixels = improc.getFloatArray();

Congrats, you now have a multi-dimensional array representing the pixels after edge detection.

Pithecanthropus