Inner boundary tracing

edge_linking.m

function output = my_edgelinking(image, row, col)
    output = [row col;];
    image(row, col) = 0;
    dir = 7;
    while (1)
        
        [row, col, next_found, dir] = find_next_dir(row, col, dir, image);
        if (~next_found)
            break;
        end
        if (output(1, 1) == row && output(1, 2) == col)
            break;
        end
        image(row, col) = 0;
        output = [output; row col;];
    end
    
    
    function iimage = fill_image(ih, iw, iimage)
        [height, width] = size(iimage);
        il = iw > 2;
        ir = iw < width - 1;
        iu = ih > 2;
        id = ih < height - 1;
        if (il && iimage(ih, iw - 2) == 1)
            iimage(ih, iw - 1) = 1;
        end
        if (ir && iimage(ih, iw + 2) == 1)
            iimage(ih, iw + 1) = 1;
        end
        if (iu && iimage(ih - 2, iw) == 1)
            iimage(ih - 1, iw) = 1;
        end
        if (id && iimage(ih + 2, iw) == 1)
            iimage(ih + 1, iw) = 1;
        end
        if (il && iu && iimage(ih - 2, iw - 2) == 1)
            iimage(ih - 1, iw - 1) = 1;
        end
        if (il && id && iimage(ih + 2, iw - 2) == 1)
            iimage(ih + 1, iw - 1) = 1;
        end
        if (ir && iu && iimage(ih - 2, iw + 2) == 1)
            iimage(ih - 1, iw + 1) = 1;
        end
        if (ir && id && iimage(ih + 2, iw + 2) == 1)
            iimage(ih + 1, iw + 1) = 1;
        end
            
    function [frh, frw, frfound, frp] = find_next_dir(fh, fw, fdir, fimage)
        [height, width] = size(fimage);
        frw = fw;
        frh = fh;
        signs = zeros(1, 8);
        if (fw < width && fimage(fh, fw + 1))
            signs(1) = 1;
        end
        if (fw < width && fh > 1 && fimage(fh - 1, fw + 1))
            signs(2) = 1;
        end
        if (fh > 1 && fimage(fh - 1, fw))
            signs(3) = 1;
        end
        if (fh > 1 && fw > 1 && fimage(fh - 1, fw - 1))
            signs(4) = 1;
        end
        if (fw > 1 && fimage(fh, fw - 1))
            signs(5) = 1;
        end
        if (fw > 1 && fh < height && fimage(fh + 1, fw - 1))
            signs(6) = 1;
        end
        if (fh < height && fimage(fh + 1, fw))
            signs(7) = 1;
        end
        if (fh < height && fw < width && fimage(fh + 1, fw + 1))
            signs(8) = 1;
        end
        frfound = 0;
        frp = mod(fdir + 1, 8) + 1;
        while (1)
            if (signs(frp))
                frfound = 1;
                break;
            end
            frp = mod(frp, 8) + 1;
            if (frp == mod(fdir + 1, 8) + 1)
                break;
            end
        end
        switch (frp)
            case 1
                frw = frw + 1;
            case 2
                frw = frw + 1;
                frh = frh - 1;
            case 3
                frh = frh - 1;
            case 4
                frh = frh - 1;
                frw = frw - 1;
            case 5
                frw = frw - 1;
            case 6
                frw = frw - 1;
                frh = frh + 1;
            case 7
                frh = frh + 1;
            case 8
                frw = frw + 1;
                frh = frh + 1;
        end
        frp = frp - 1;
        if (mod(frp, 2) == 1)
            frp = mod(frp + 6, 8);
        else
            frp = mod(frp + 7, 8);
        end
        
    
    
    
    
%in this function, you should finish the edge linking utility.
%the input parameters are a matrix of a binary image containing the edge
%information and coordinates of one of the edge points of a obeject
%boundary, you should run this function multiple times to find different
%object boundaries
%the output parameter is a Q-by-2 matrix, where Q is the number of boundary 
%pixels. B holds the row and column coordinates of the boundary pixels.
%you can use different methods to complete the edge linking function
%the better the quality of object boundary and the more the object boundaries, you will get higher scores
% 1   1   1
%   1 1 1
% 1 1 1 1 1
%   1 1 1
% 1   1   1