How to write a .bmp format file?

Hi, all

I am using Principal Component Analysis (PCA) to analyze a 2D facial image database (ORL database). Here is my code

-----------------------------------------

    data = zeros(400, 10304);

    for i = 1:400

        name = ['face' num2str(i) '.bmp'];
        temp = imread(name);
        temp = reshape(temp, 1, 10304);
        data(i, :) = temp;
    end

    meanface = mean(data, 1);

    data = data - repmat(meanface, 400, 1);

    intermat = (data * data') / (400-1);
    [intervec, val] = eig(intermat);

    pc = data'*intervec;
    pc = pc';

for i = 1:400
    pc(i,:) = pc(i,:) / sqrt(dot(pc(i,:), pc(i,:)));
    sd(i) = sqrt(val(i,i));
    eigenvalue(i) = val(i,i);
end

pc = flipud(pc);
sd = fliplr(sd);
eigenvalue = fliplr(eigenvalue);

---------------------------------------

After PCA, I try to write an eigenface in a .bmp image

face = meanface + sd(1) * pc(1,:);
face = reshape(face, 112, 92);
imwrite(face, 'eigenface.bmp');

However, what I get is a pure white image. Then I try to write meanface alone, and the result is all the same, a white plane. Till I try to write a principal component alone, the contour of a human face reveals.

Can anyone help me to find my mistake?

Many thanks in advance.

Sincerely Wenlong

[Jan]

While the PCA part of the code is not relevant for the actual problem, it would be more helpful if you explain 1. the range and type of the variable "face" and 2. how you determine that the image is white.

Perhaps there is a confusion with UINT8 and DOUBLE types of the image? Or the re-import fails.

Answer 1

[Image Analyst]

Try this:

face_uint8 = uint8(255 * mat2gray(face));
fullFileName = fullfile(folder, 'eigenface.bmp'); % Or call uiputfile() if you want.
imwrite(face_uint8, fullFileName);