How i can scale an image using scalle matrix that i determined?

I think if i scale/shear a image matrix, it calculate the position of (x,y) not the value of (x,y) - is it true? I want scale an image using :

scaleMatrix = [0,0; 0,0.5];
a = imread('rectangle.bmp');
a = rgb2gray(a);
b = im2bw(a);
newImage = zeros(size(b));

My problem is how can i scale the matrix image using scaleMatrix that i determine before? and the result is store in newImage. I confused how i can calculate the location of each matrix image with the scaleMatrix.

Standar formula for scale that i know is (x',y') = (x,y).(Sx,0; 0,Sy).

thx.

Answer 1

[Walter Roberson]

The formula (x',y') = (x,y).(Sx,0; 0,Sy) is to work on coordinate pairs such as for a vector geometry.

To rescale y by 1/2, consider using

 newImage = imresize(b, size(b) .* [1 1/2]);

[Cahaya]

Hmmm..,ok i'll try it..

And, how if i want to shear a an image with 45 degrees, can i do that? is there any example code?

[Image Analyst]

http://blogs.mathworks.com/steve/2006/08/04/spatial-transformations-defining-and-applying-custom-transforms/