How to add multiple gray images without getting white output?

Hello.

So, i've written short Matlab code which should take all photos from folder, and merge them.

Problem is, i don't know how to add multiple gray images without getting white output.

Currently i'm trying with multiplying images by alpha, but i need to rescale it everytime i change amount of images... Is there any other way to deal with this problem?

My code below:

clc

clear all

folder = ('C:\Users\Kerak\Desktop\MATLAB\lfw');

S = dir;

A = zeros(250, 250);

A = im2uint8(A);

ile = numel(S);

alpha = .01;

for i = 3:50

    if(S(i).isdir)
        cd (S(i).name);
            Foty = dir;
            ilefot = numel(Foty);
            for j = 3:ilefot
                image = imread(fullfile(folder, S(i).name, Foty(j).name));
                image = rgb2gray(image);
                A = A + image*alpha;
            end
        cd ('..');
    end
end

imshow(A);

Any ideas? Thanks

Answer 1

[Image Analyst]

Don't use image for a variable name since it's the name of a very important built in function. That could be one reason why it doesn't work (but it's not). The reason it doesn't work is that A is a double matrix and all the values are > 1. If imshow() gets a double matrix, it expects it (rightly or wrongly) to be in the range 0-1. To fix, add [] after the (badly-named) A in imshow(). Call A "sumImage" to be more descriptive. To fix:

fullFileName = fullfile(folder, S(i).name, Foty(j).name);
thisImage = double(imread(fullFileName));
[rows, columns, numberOfColorChannels] = size(thisImage);
if numberOfColorChannels > 1 % Only call rgb2gray if it's really RGB, otherwise you'll get an error.
    thisImage = rgb2gray(image);
end
if rows == size(sumImage, 1) && columns == size(sumImage, 2)
    sumImage = sumImage + thisImage*alpha;
else
    message = 'Size mismatch';
    uiwait(errordlg(message));
end

After the loop, use

imshow(sumImage, []);

[Luq Ops]

Thanks for fast answer.

Yes, these variable names are poor, sorry for that.

Unfortunately, i've wrongly described problem. What i meant is that when i'm adding gray images, the output IMAGE is white, because addition. That's why there's alpha variable, to nullify that problem, and it's working.

But now, i need to manually change alpha variable everytime when i'm changing loop range.

For example alpha = 0.01 works for loop of range 3:50, but when i increase loop range to 3:150 i need alpha = 0.005.

Is there any way to merge many gray images without getting white image as a output?

I've forgotten mention that i'm using "Faces in the wild", which is database of face images and this code is creating face template from these.