Need help identifying shape on image

Hello, I need a little help with identifying shape of the edges on multiple images like this:

The goal: Is to obtain a binary image highlighting only the edges something like this:

My gratitude to anyone who is smarter than my and can figure it out.

Answer 1

[Image Analyst]

Did you try edge() on the green channel?

[r, g, b] = imsplit(rgbImage);
edgeImage = edge(g);
imshow(edgeImage);

[Oscar Loch]

Gonna try this out right now, thanks, I'll tell you what I obtained

[Oscar Loch]

Used your suggestion, this is what I got:

It kinda leaves with less white dots in the area where we need to get the edges.

[Image Analyst]

Yeah, there are tons of edges. What did you try? Did you try to vary the input options, like the filter window width, and other things? Maybe try imgradient(). Or try imbinarize(), maybe with the 'adaptive' option and then try thresholding and using bwmorph().

[Oscar Loch]

Yes, this is what I tried:

This is the input image I used:

This was the result :

And the code I used is down on this comment, as you can see on the result image it doesn´t accomplish the goal, maybe there is another way that is more effective than the one I'm using but I haven't been able to come up with it. (PD: thank you so much for your interest and help)

   Input_img = imread('laser_shot468.JPG');

    Input_img =255-Input_img   %negative

    Input_img = imadjust(im2gray(Input_img));  %grey and adjust
   
    Input_img = imbinarize(Input_img);   %binary

    Input_img = bwareaopen(Input_img,14400); %removes small objects
    
    Input_img =edge(Input_img,'Canny',0.76);    %edges of binary

    Input_img = bwareaopen(Input_img,10);  %removes small objects again
    
    imshow(Input_img);
    
    imwrite(Input_img,'Imagen.png')

[Image Analyst]

Those look like edges to me. Why do you say they are not edges? Do you actually want dark regions instead of edges?

[Oscar Loch]

Exactly, maybe I explained my self wrong. But what I need is a white line as it appears on the original question goal , where it highlights the edge of the dark regions, I tought maybe using the areas where is black would be useful but as you can see on the original post there is also dark regions inside

[Image Analyst]

You are getting the edges of the dark regions. If you want the centerlines of the dark regions, instead of the edges of the bight/dark boundary, you should threshold, say with imbinarize(), and then use bwskel() instead.