Thread Subject: Populating a matrix with pixel values

Hello everyone.

I have a question, and I hope that someone out there can help me out. I am trying to use for loops to populate a matrix with pixel values from a given image.

Given an image, and an x and y coordinate, I want to generate a 5x5 matrix centered on (x,y), populated by pixel intensity values from the image.

A sample of my code:

for a = 0:6
   matrix(r,:)=image((y+2)-a, (x-2):(x+2));
   a=a+1;
end

Where matrix is the 5x5 matrix that I am trying to generate.

As you can see from the above code, I want to generate a 5x5 matrix, populating each matrix row wise, with the pixel intensity of the image based upon changing the coordinates. However, whenever I run this section of code in MatLab, the error i receive says:

??? Error using ==> image
Incorrect number of arguments specified.

Error in ==> generatematrix at 21
    clutter7(r,:)=image((y+3)-a,(x-3):(x+3));

I'm assuming that this message means that MatLab does not allow the image(x,y) command to retrieve information using the ':' operator. Am I wrong in this assumption? Does anybody knows if there is another way to automatically generate this matrix through the use of a for loop or some other operator?

m. k:
<SNIP extracting data from an image...

one of the solutions

% the image
     img=reshape(1:25,[5,5]);
     rc=2; % submat center: row
     cc=4; % submat center: col
     ms=3; % submat size: 3x3 == odd
% the engine
     ns=floor(ms/2);
% ...error checking comes here!
     m=img(rc-ns:rc+ns,cc-ns:cc+ns);
% the result
     img
     m

us

thanks for the help. i have another question though. how do i reshape the matrix if in your code, the '1:25' values were placed with pixel intensity values pulled from specific x and y coordinates from an image? Would you know how to pull those pixel values from an image and reshape them?

thanks,

m.k.

"us " <us@neurol.unizh.ch> wrote in message <f8nqrp$g01$1@fred.mathworks.com>...
> m. k:
> <SNIP extracting data from an image...
>
> one of the solutions
>
> % the image
> img=reshape(1:25,[5,5]);
> rc=2; % submat center: row
> cc=4; % submat center: col
> ms=3; % submat size: 3x3 == odd
> % the engine
> ns=floor(ms/2);
> % ...error checking comes here!
> m=img(rc-ns:rc+ns,cc-ns:cc+ns);
> % the result
> img
> m
>
> us