% Stitch two images together with a multiresolution spline,
% using Laplacian pyramids.
clear all
close all

n = 8;  % Number of levels in pyramid

% First image (image A)
IA = imread('apple_real.jpg');
IA = rgb2gray(IA);

% Create a Laplacian pyramid (a cell array of images)
G{1} = double(IA);  % Lowest level of Gaussian pyramid
for i=2:n
    G{i} = imresize(G{i-1}, 0.5); % apply lowpass, then scale by 0.5
    Gs = imresize(G{i}, 2,'bicubic');  % scale up by factor of 2
    LA{i-1} = G{i-1} - Gs;      % Laplacian pyramid
end
LA{n} = G{n};   % Highest level is just the coarsest resolution image

for i=1:n
    figure, imshow(LA{i}, []);
end
pause


% Second image (image B)
IB = imread('apple_logo.jpg');
IB = rgb2gray(IB);

% Create a Laplacian pyramid (a cell array of images)
G{1} = double(IB);      % Lowest level of Gaussian pyramid
for i=2:n
    G{i} = imresize(G{i-1}, 0.5); % apply lowpass, then scale by 0.5
    Gs = imresize(G{i}, 2,'bicubic');  % scale up by factor of 2
    LB{i-1} = G{i-1} - Gs;  % Laplacian pyramid
end
LB{n} = G{n};   % Highest level is just the coarsest resolution image

for i=1:n
    figure, imshow(LB{i}, []);
end
pause


% Merge pyramids.  At each level, use the left half from image A, and the
% right half from image B.  For the center column, average them.
for i=1:n
    A = LA{i};
    B = LB{i};
    w = size(A,2);      % Image width at this level
    w2 = round(w/2);    % Center column
    LS{i}(:,1:w2-1) = A(:,1:w2-1);  % Use left half from image A
    LS{i}(:,w2+1:w) = B(:,w2+1:w);  % Use right half from image B
    LS{i}(:,w2) = (A(:,w2) + B(:,w2))/2;    % Average the center columns
end

% Reconstruct image from Laplacian pyramid
Ireconstructed = LS{1};
for i=2:n
    I = imresize(LS{i}, 2^(i-1), 'bicubic');
    Ireconstructed = Ireconstructed + I;
end

figure, imshow(Ireconstructed,[]);