How do i use pca on image?

is this code correct? ...................................................

function [signals,PC,V] = pca() I=imread('G:\Users\farahnaz\Downloads\018.jpg'); b= im2double(I); imshow(b, []); [irow, icol] = size(b); data = reshape(b',irow*icol,1);

[M,N] = size(data);

mn = mean(data,2);

data = data - repmat(mn,1,N);

covariance = cov(data)';

[PC, V] = eig(covariance);

V = diag(V);

[junk, rindices] = sort(-1*V);

V = V(rindices); PC = PC(:,rindices);

[Image Analyst]

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup