how can i measure the longest point of my lightning image?

[darova]

What do you mean longest point

[Neptune16]

form the red point to any of these orange point maybe.

[Matt J]

Maybe? You don't know?

[Neptune16]

no, I mean is there any automatic methods that the code will find the longest point as I mark with orange colour above.

[Matt J]

The straight line distance from red to orange, or the distance when walking along the lightning fork? If the latter, there are several implementations of Dijkstra's algorithm on the file exchange

https://www.mathworks.com/matlabcentral/fileexchange?q=Dijkstra%27s+Shortest+Path

Answer 1

[Image Analyst]

One way to find the longest spine might be to compute the skeleton and endpoints with bwmorph(). Then compute distance between all identified endpoints with bwdistgeodesic(). See Steve's Image Processing blog

Then find out which pair of endpoints had the longest distance.

[Neptune16]

hello and good day, sir @imageanalyst. I have posted a new question 5 days ago. I would like to ask you a favour to help me with it. kindly please see the latest question I've asked in my profile. thank you for your time and consederation.

Answer 2

[darova]

Draw black (0,0,0) line you want to calculate the length

See attached script

[Neptune16]

I had tried your coding, sir. but the outcome is not the same as yours.

[darova]

Did you draw black line (0;0;0) ?

[Neptune16]

what do you mean "Draw black (0,0,0) line you want to calculate the length" , sir?

[darova]

When you draw black line (color - (0;0;0), look in paint for example) script takes only black pixels

Then imfil() function clears single pixels we dont want

From thick line we get thin with bwmorph()

Using again bwmorph() to get clear line

Find nonzero indices (coordinates) to get a curve

[Image Analyst]

If you're going to draw a black line with paint, then you might as well use imfreehand() in MATLAB. I think he was looking for an automatic way, like me (below) or Matt J (above in comments section) suggested. That said, sometimes it's more time effective to employ user-assisted image analysis than trying months or years to get an automatic method (luckily this application won't take anywhere near that long).

[darova]

thank you