imagerotate.m

image = imread('lena512.bmp'); %reading image

figure(1), clf, hold on  % clears current figure window, hold on is the command to retain the 
                         % current plot and certain axes.
subplot(1,2,1) % plots the existing image
imshow(image); % shows image

degree = 35; % last 2 digits of ID number (2016B4A80535H)

switch mod(degree, 360)  % switch case for generalized rotations
    % Special cases
    case 0
        imagerot = image;
    case 90
        imagerot = rot90(image);
    case 180
        imagerot = image(end:-1:1, end:-1:1);
    case 270
        imagerot = rot90(image(end:-1:1, end:-1:1));

    % General rotations
    otherwise

       
        a = degree*pi/180;  % Convert to radians 
        R = [+cos(a) +sin(a); -sin(a) +cos(a)]; % create transformation matrix

        % Figure out the size of the transformed image
        [m,n,p] = size(image);
        dest = round( [1 1; 1 n; m 1; m n]*R );  
        dest = bsxfun(@minus, dest, min(dest)) + 1;  % bsxfun applies the element wise binary operation specified by function handle fun
        imagerot = zeros([max(dest) p],class(image));

        % Map all pixels of the transformed image to the original image
        for ii = 1:size(imagerot,1)
            for jj = 1:size(imagerot,2)
                source = ([ii jj]-dest(1,:))*R.';
                if all(source >= 1) && all(source <= [m n])

                    % Get all 4 surrounding pixels
                    C = ceil(source);
                    F = floor(source);

                    % Compute the relative areas
                    A = [...
                        ((C(2)-source(2))*(C(1)-source(1))),...
                        ((source(2)-F(2))*(source(1)-F(1)));
                        ((C(2)-source(2))*(source(1)-F(1))),...
                        ((source(2)-F(2))*(C(1)-source(1)))];

                    % Extract colors and re-scale them relative to area
                    cols = bsxfun(@times, A, double(image(F(1):C(1),F(2):C(2),:)));

                    % Assign colors to transformed image                   
                    imagerot(ii,jj,:) = sum(sum(cols),2);

                end
            end
        end        
end

subplot(1,2,2)  % Add transformed image to plot
imshow(imagerot);  % Show plot