load_face_images.m

function [image_stack, scriptV] = load_face_images(image_dir)
% LOAD_FACE_IMAGES Load the set of face images.  
%   image_dir: path to the image directory
%
%   image_stack: all images stacked along the 3rd channel
%   scriptV: light directions
%
% Source: Marc Pollefeys, 2006

num_images = 64;

% get ambient image
filename = [image_dir 'yaleB02_P00_Ambient.pgm'];
ambient_image = getpgmraw(filename);
[h, w] = size(ambient_image);

% get list of all other image files
d = dir([image_dir 'yaleB02_P00A*.pgm']);

% randomly select num_images number of images
filenames = {d(:).name};
total_images = numel(filenames);

if num_images <= total_images
    filenames = {d(randperm(numel(d), num_images)).name};
else
    fprintf('Total available images is less than specified.\nProceeding with %d images.\n', total_images)
end

Nimages = numel(filenames);

% arrays to store the angles of light sources
Ang = zeros(2, Nimages);

% create array of illuminated images
image_stack = zeros(h, w, Nimages);

for j = 1 : Nimages
	m = strfind(filenames{j},'A')+1;
	Ang(1,j) = str2double(filenames{j}(m:(m+3)));
	m = strfind(filenames{j},'E')+1;
	Ang(2,j) = str2double(filenames{j}(m:(m+2)));
	image_stack(:,:,j) = getpgmraw([image_dir filenames{j}]);
end

[X,Y,Z]= sph2cart(pi*Ang(1,:)/180,pi*Ang(2,:)/180,1);
scriptV = [Y;Z;X];
scriptV = scriptV';


%% preprocess the data: 

% subtract ambient_image from each image in imarray
image_stack = bsxfun(@minus, image_stack, ambient_image);

% make sure no pixel is less than zero
image_stack(image_stack < 0) = 0;

% rescale values in imarray to be between 0 and 1
minVal = min(image_stack(:));
maxVal = max(image_stack(:));
image_stack = (image_stack - minVal) / (maxVal - minVal);

end