PCA OF AN IMAGE...

I want to find PCA of an image... but when i run the code i get following error..

Error using - Integers can only be combined with integers of the same class, or scalar doubles. Error in pca (line 26) data = data - repmat(mn,1,N);

here is the code....'

function [signals,PC,V] = pca()

 I = imread('C:\Users\div\Pictures\Picture1.png');

    I = rgb2gray( I);

    [irow, icol] = size(I);

   data = reshape(I',irow*icol,1);

% [sR ,sC ,eR ,eC] = deal(1, 3, 2, 4);

% Compute the sum over the region using the integral image.

% PCA1: Perform PCA using covariance.

% data - MxN matrix of input data

% (M dimensions, N trials)

% signals - MxN matrix of projected data

% PC - each column is a PC

% V - Mx1 matrix of variances

[M,N] = size(data);

% subtract off the mean for each dimension

mn = mean(data,2);

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

% calculate the covariance matrix

covariance = 1 / (N-1) * data * data;

% find the eigenvectors and eigenvalues

[PC, V] = eig(covariance);

% extract diagonal of matrix as vector

V = diag(V);

% sort the variances in decreasing order

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

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

% project the original data set

signals = PC * data;

Answer 1

[Image Analyst]

That is a dangerous way that you used size(). See Steve's blog: http://blogs.mathworks.com/steve/2011/03/29/even-more-information-about-the-size-function/

A common way to deal with your error is to just convert everything to double. But if you do then you need to use [] to see your images or else they will show up as all white because double images are expected to be in the range 0-1.

imshow(doubleImage, []);

The [] will adjust the display to handle whatever range your array may have, and not require it to be in the 0-1 range.

[divya]

function [signals,PC,V] = pca()

 I = imread('C:\Users\div\Pictures\Picture1.png');

    data = rgb2gray( I);

data=double(data);

    [irow, icol] = size(I);

   data = reshape(I,irow*icol,1);

imshow(data);

% [sR ,sC ,eR ,eC] = deal(1, 3, 2, 4);

% Compute the sum over the region using the integral image.

% imageArray = reshape(imageArray',9,1)

% PCA1: Perform PCA using covariance.

% data - MxN matrix of input data

% (M dimensions, N trials)

% signals - MxN matrix of projected data

% PC - each column is a PC

% V - Mx1 matrix of variances

[M,N] = size(data);

% subtract off the mean for each dimension

mn = mean(data,2);

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

% calculate the covariance matrix

covariance = 1 / (N-1) * (data) * (data);

% find the eigenvectors and eigenvalues

[PC, V] = eig(covariance);

% extract diagonal of matrix as vector

V = diag(V);

% sort the variances in decreasing order

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

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

% project the original data set

signals = PC * data; after resolving that i get another error

_*Error using * Inner matrix dimensions must agree.

Error in pca (line 33) covariance = 1 / (N-1) * (data) * (data);*_

please anybody can tell me how to exactly find the pca of image pixel data

[Image Analyst]

Maybe you mean

covariance = data .^2  ./ (N-1);

I'm not sure. Use the dot if you want element by element operations.

[divya]

Undefined function 'eig' for input arguments of type 'uint8'.

Error in pca (line 46) [PC, V] = eig(covariance);

still getting this error.....:(

[Image Analyst]

So cast it to double, or do

which eig

Answer 2

[yagnesh]

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

Answer 3

[farahnaz]

please use this cod :

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);

[Shaveta Arora]

how to show the image after this using principal components. Please answer!!

[Image Analyst]

With

imshow(pcimage, [])

Make sure you get your PC image as a 2D image.

[Shaveta Arora]

pls elaborate about the pcimage variable. how to get PC image as 2D

[Image Analyst]

I don't see how he's getting PC images. There aren't any. You can see my attached demo if you want.

Answer 4

[Shaveta Arora]

actually I want to recover the image using principal components after the following instruction:

% project the original data set

signals = PC * data;

pls help me in recovering the image.