MATLAB: How to compare two 3D matrices element-wise

comparisonmatrix

I have two RGB images (3D matrix: x, y, z) of the same size, and I wanted to compare the corresponding values.

Suppose there are two matrices A and B, both have size (4,5,3).

I want a 2D mask (logical image) that represents the (x,y) points where matrix A is less than matrix B in all 3 values of the third (z) dimension.

So for example the mask(4,4) = 1 if:

A(4,4,1) < B(4,4,1)
A(4,4,2) < B(4,4,2)
A(4,4,3) < B(4,4,3)

I tried this but it doesn't work, because the resulting matrix (ALessThanB) is 3D logical:

ALessThanB = A < B;

How can I make this comparison only along the third dimension?

Best Answer

Use the all function. You'll want to specify the optional dim input argument as well as the required A input argument (the data.)

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squeeze()

transpose()

MATLAB: Is there an alternative to “find” for non-integer values

Check if it's within a tolerance, as recommended by the FAQ. Try this:

targetValue = 4.443;
tolerance = 0.01;
M = [2.334 3.554
     4.443 4.554
     3.245 5.332
     4.443 2.443]
   diffM = abs(M(:, 1) - targetValue)
   % Find rows within tolerance of the target value in row 1.
   rowsToExtract = diffM < tolerance
   % Extract only those rows:
   extractedRows = M(rowsToExtract, :)

In the command window you'll see:

M =
                   2.334                     3.554
                   4.443                     4.554
                   3.245                     5.332
                   4.443                     2.443
diffM =
                   2.109
                       0
                   1.198
                       0
rowsToExtract =
   0
   1
   0
   1
extractedRows =
                   4.443                     4.554
                   4.443                     2.443

Best Answer

Related Solutions

MATLAB: Reshape 3d to 2d array

MATLAB: Is there an alternative to “find” for non-integer values

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