creating a mask matrix using matlab

[ashish]

Hi,
First how do i create a mask matrix with zeroes at four X*X corners and ones at the remaining corners?
Next,How do I multiply the mask matrix at the four corners with the input matrix so that it becomes zero at those specified X*X four corners and ones at the remaining corners?

Sounds simple but I am finding it little difficult to comprehend.
Thanks.

[Image Analyst]

"ashish " <ashi...@hotmail.com>

Try this:

clc;
close all;
% Create some arbitrary array for demo.
imageArray = magic(5)
[rows cols] = size(imageArray);
% Create a mask array the same size that is all 1's.
maskArray = ones(rows, cols);
% Zero out the corners.
maskArray(1, 1) = 0;
maskArray(1, cols) = 0;
maskArray(rows, 1) = 0;
maskArray(rows, cols) = 0
% Dot-multiply to mask the image.
maskedImageArray = imageArray .* maskArray

[Walter Roberson]

I'd be tempted to use sub2ind() to shorten that code.

maskArray = ones(rows, cols);
maskArray(sub2ind([rows, cols], [1 1 rows rows], [1 cols 1 cols])) = 0;

[ashish]

Hi Image Analyst
I understand your example but How do i get four corners i.e submatrices as zeroes rather than just four corner elements as zero?
Thanks a lot.

"Image Analyst" <imagea...@mailinator.com> wrote in message <gqbb4e$8an$1...@fred.mathworks.com>...

[Image Analyst]

"ashish " <ashi...@hotmail.com>
Just use normal, run-of-the-mill indexing:

clc;
close all;
% Create some arbitrary array for demo.

imageArray = magic(8)

[rows cols] = size(imageArray);
% Create a mask array the same size that is all 1's.
maskArray = ones(rows, cols);

% Zero out the corners in a 2x2 submatrix at each corner.
submatrixSize = 2;
maskArray(1:submatrixSize, 1:submatrixSize) = 0;
maskArray(1:submatrixSize, (cols - submatrixSize + 1):cols) = 0;
maskArray((rows - submatrixSize + 1):rows, 1:submatrixSize) = 0;
maskArray((rows - submatrixSize + 1):rows, (cols - submatrixSize + 1):cols) = 0

[Image Analyst]

Of course, just as I zeroed out the corners of the maskArray, you could do the same thing to the image array directly and skip the multiplication step. Why multiply a bunch of numbers in the middle when you don't need to (unless you need to save the mask or original image to use later for some reason)?

[ashish]

Thanks a lot Image Analyst. I was trying to do the same with the first submatrix but I was stuck with the other three submatrices and you replied by the time i was think about other ones.

Thanks once again, I learned something new today.

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