How can I access a submatrix as an array inline?

I am trying to avoid adding extra/unneeded variables and code to my matlab scripts.

I have noticed that when I access a submatrix inline, I will get a different result than if I make a separate variable of the submatrix beforehand and use the colon operator in my reference.

For Example: -Let A be a 576x720x3 matrix. B=A(50:100,50:100,1); [a1,b1]=histc(A(50:100,50:100,1),0:255); [a2,b2]=histc(B(:),0:255);

This results in a case where a1 != a2 and b1 != b2. They have the same basic values, but a1 & b1 appear to be groups of histograms of smaller data sets (51x51 matrix input), while a2 & b2 are a single histogram of the full submatrix dataset (51x51=2601 elements).

Does anyone know how to get the [a2,b2] result without using the extra variable B? (i.e. is there a way to use an inline reference to a submatrix of A that returns the data as a single column?)

Thanks, Sean

Answer 1

[Sean de Wolski]

The problem is that B(:) is not the same shape as B which is equal to A(..).

To fix:

A = imread('peppers.png');
B=A(50:100,50:100,1); 
[a1,b1]=histc(reshape(A(50:100,50:100,1),[],1),0:255); 
[a2,b2]=histc(B(:),0:255);

isequal(a1,a2)
isequal(b1,b2)

reshape A(..) before the call to histc