get the matrix values under a line

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Armindo
Armindo on 11 Oct 2015
Commented: Rahand Dalshad on 2 May 2021
Hi,
I have a matrix of data (120x90) that I plot and then I draw a diagonal line by doing something like:
plot([x1,x2],[Y1,Y2],'g.');
I need to be abe to determine all the matrix values under the line. Any idea about how to perform this efficiently?

Answers (3)

Image Analyst
Image Analyst on 12 Oct 2015
If you have the Image Processing Toolbox, you can get this information from the function improfile().
improfile(I,xi,yi,n) returns pixel intensity values, where n specifies the number of points to include.
c = improfile(___) returns the intensity values in c, an n-by-1 vector, if the input is a grayscale intensity image, or an n-by-1-by-3 array if the input is an RGB image.
[cx,cy,c] = improfile(I,xi,yi,n) additionally returns the spatial coordinates of the pixels, cx and cy, of length n.
  3 Comments
Image Analyst
Image Analyst on 13 Oct 2015
You're welcome. Can you go ahead and "Accept this answer" then? Thanks!
Rahand Dalshad
Rahand Dalshad on 2 May 2021
Dear Image Analyst,
I want to thank you personally for all your help, suggestions and solutions to Matlab issues and questions. Lately, I am doing much images post-processing of optical obtained images and data. Wherever I stuck and google for a proper solution, I find the best and easiest solution from you.
Thank you again and keep up the good work
Regards form Germany
Rahand

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Star Strider
Star Strider on 11 Oct 2015
You would have to define every (x,y) pair along the line, in terms of the row and column values of the matrix coordinates. That will likely be straightforward when you derive an equation for the line.
I am not certain what information you want from the matrix, but you might also consider using the interp2 function if you want to interpolate the values of the matrix.
  4 Comments
Armindo
Armindo on 12 Oct 2015
Your are completly right. I did not explain myself properly and I apologize for that. I belive that your suggestion (about determine the intersections of the line with a grid of coordinates) would work perfectly I will give it a try. Thank you very much for the help and code.
Star Strider
Star Strider on 12 Oct 2015
My pleasure.
I tested that code thoroughly so it should be robust. I’ll do my best to help you adapt it if necessary, but I wrote it years ago (and haven’t used it much since), so I’d have to remember what I did.

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William Chamberlain
William Chamberlain on 17 Oct 2018
  1 Comment
Image Analyst
Image Analyst on 17 Oct 2018
Using improfile() with the 'nearest' option would also do that, if he wanted to go to the nearest pixel instead of doing subpixel interpolation.

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