MATLAB: Problem with cumsum

cumsum

Hi guys,
I am trying to write a code to correct the background for an image. I used the formula given in the paper "Methods of Digital Video Microscopy for Colloidal Studies" by Crocker and Grier.
The formula is
Ib(x,y)=(constant)*[?I(x+i,y+j)] %the summation goes from i,j= -w to +w; w is predefined. 'I' is the original image and 'Ib' the background corrected image.
I thought of using "cumsum" since we need to sum up the components of the rows and columns of a matrix basically to decrease the computation time. However I am getting an error and I am clueless about what I am doing wrong.
The code is given below
I=imread('*.tif');
I=rgb2gray(I);
sizeim=size(I);                     %computes size of image
Iback=zeros(sizeim(1),sizeim(2));   %Iback same size as I but with zeros
B=1/((2*w+1)^2);                    %constant used for division
w=5;
for i=w+1:sizeim(1)-w
      for j=w+1:sizeim(2)-w
          temp=cumsum(cumsum(I(i-w:i+w,j-w:j+w),1),2);
          Iback(i,j)=temp(2*w+1,2*w+1)/B;
      end
  end
I get the error message "??? Undefined function or method 'cumsum' for input arguments of type 'uint8'"
Can anyone tell me what I am doing wrong? Your help is truly appreciated.
NS

Best Answer

CUMSUM does not work for data that isn't single or double. You can write your own function to do this, or cast the data to single before passing to CUMSUM. Note however, that you will have to figure out what to do with overflow! The cumulative sum in uint8 may easily go over 255.
intmax('uint8')
You could also convert your image to have a datatype which has a larger range...
Related Question