calculate_inliers.m

function [num_of_inliers, matched_x_coordinate] = calculate_inliers(input1, input2)
    %input1 = 'uttower_left.jpg';
    %input2= 'uttower_right.jpg';
    %input1 = 'assignment3_data/hill/1.JPG';
    %input2 = 'assignment3_data/hill/2.JPG';
    neighbor_size = 5; % (2x+1)*(2x+1) pixels total
    iterations = 2000;
    top = 200;
    input_rgb_left = imread(input1, 'jpg');
    input_rgb_right = imread(input2, 'jpg');
    input_left = rgb2gray(input_rgb_left);
    input_right = rgb2gray(input_rgb_right);
    input_left = im2double(input_left);
    input_right = im2double(input_right);
    [left_height, left_width] = size(input_left);
    [right_height, right_width] = size(input_right);
    %Compute Harris corners
    [output_left, row_left, col_left] = harris(input_left, 3, 0.05, 3, 1); 
    [output_right, row_right, col_right] = harris(input_right, 3, 0.05, 3, 1);

    [num_of_corners_left, tmp] = size(row_left);
    [num_of_corners_right, tmp] = size(row_right);
    %Compute Descriptors
    new_row_left = [];
    new_col_left = [];
    for i = 1:num_of_corners_left
        if((row_left(i) > neighbor_size) && (col_left(i) > neighbor_size) && (row_left(i) < left_height-neighbor_size-1) && (col_left(i) < left_width-neighbor_size-1))
            new_row_left = [new_row_left; row_left(i)];
            new_col_left = [new_col_left; col_left(i)];
        end
    end
    row_left = new_row_left;
    col_left = new_col_left;

    new_row_right = [];
    new_col_right = [];
    for i = 1:num_of_corners_right
        if((row_right(i) > neighbor_size) && (col_right(i) > neighbor_size) && (row_right(i) < right_height-neighbor_size-1) && (col_right(i) < right_width-neighbor_size-1))
            new_row_right = [new_row_right; row_right(i)];
            new_col_right = [new_col_right; col_right(i)];
        end
    end
    row_right = new_row_right;
    col_right = new_col_right;
    [number_of_corners_left, tmp] = size(row_left);
    [number_of_corners_right, tmp] = size(row_right);

    descriptor_left = zeros(number_of_corners_left, (2*neighbor_size+1)^2);
    descriptor_right = zeros(number_of_corners_right, (2*neighbor_size+1)^2);

    for i = 1:number_of_corners_left
        descriptor_left(i,:) = reshape(input_left(row_left(i)-neighbor_size:row_left(i)+neighbor_size, col_left(i)-neighbor_size:col_left(i)+neighbor_size), 1, (2*neighbor_size+1)^2);
    end

    for i = 1:number_of_corners_right
        descriptor_right(i,:) = reshape(input_right(row_right(i)-neighbor_size:row_right(i)+neighbor_size, col_right(i)-neighbor_size:col_right(i)+neighbor_size), 1, (2*neighbor_size+1)^2);
    end
    %Select descriptor pairs by selecting the top hundered pairs with
    %smallest pairwise distances.
    distance = zeros(number_of_corners_left, number_of_corners_right);

    for i = 1:number_of_corners_left
        for j = 1:number_of_corners_right
            distance(i, j) = dist2(descriptor_left(i, :), descriptor_right(j, :));
        end
    end

    top = min([top, num_of_corners_left, num_of_corners_right]);
    matches = [];%index_left, row_left, col_left, index_right, row_right, col_right, distance
    for i = 1:top
        [r, c] = find(distance == min(min(distance)));
        if(length(r) == 1)
            matches = [matches; r, row_left(r), col_left(r), c, row_right(c), col_right(c), min(min(distance))];
            distance(r,:) = 100;
            distance(:,c) = 100;
        end
    end
    %RANSAC
    top = size(matches, 1);
    current_match_num = 4;
    n = 1;
    while(n < iterations)
        if current_match_num == 4
            inliers = randsample(top, current_match_num);
        end
        %Homography Estimation
        A = [];
        for i = 1:current_match_num
            current_match = matches(inliers(i), :);
            xT = [current_match(3), current_match(2), 1];
            A = [A; xT*0, xT, xT*(-current_match(5))];
            A = [A; xT, xT*0, xT*(-current_match(6))];
        end
        [U, S, V] = svd(A);
        H = V(:, end);
        H1 = reshape(H, 3, 3);
        num_of_inliers = 0;
        inliers = [];
        matched_x_coordinate = [];
        for i = 1:top
            X =  H1'* [matches(i, 3); matches(i, 2); 1];
            x = X(1)/X(3);
            y = X(2)/X(3);
            if(dist2([x,y], [matches(i, 6),matches(i, 5)]) < 2)
                inliers = [inliers; i];
                matched_x_coordinate = [matched_x_coordinate; matches(i, 3), matches(i, 6)];
                num_of_inliers = num_of_inliers+1;
            end
        end
        if(num_of_inliers < 10)
            current_match_num = 4;
        else
           current_match_num = num_of_inliers;
        end
        n = n+1;
    end

    
end