Create a new matrix that contains indices for values that are larger than X

Lets say I have a matrix D and I ask the user to input a number into X. Now I need a new matrix which contains indices for values that are larger than X, what do I do to do this?

Answer 1

[Image Analyst]

[rows, columns] = find(D > X);

[Jhangir]

What is my new matrix though, I need a new matrix

[Matt Kindig]

What is the expected size of your new matrix?

[Jhangir]

“number of pixels” x “number of pixels”.

[Image Analyst]

rows and columns are your new matrices. So row(1) and column(1) are the row and column of the first element that is more than x.

If you want a binary "map" of where it's greater than just threshold:

binaryImage = D > X;

That will be a matrix of true and false (1 & 0) the same size as D. If you want just a long 1D list of values, you can do

bigValues = D(binaryImage);

But you said "new matrix which contains indices" so I gave you that. rows and columns contain the indices. To say that you want a matrix “number of pixels” x “number of pixels” shows that you don't really understand what you're asking for because that makes no sense whatsoever. If your matrix is 100 by 100 = 10000 pixels, you're not going to want a matrix that's 10000 by 10000 pixels = 100 million elements. A hundred million elements for a 100 by 100 tiny image just makes no sense.