function J=regiongrowing(I,x,y,reg_maxdist)

% This function performs "region growing" in an image from a specified

% seedpoint (x,y)

%

% J = regiongrowing(I,x,y,t) 

% 

% I : input image 

% J : logical output image of region

% x,y : the position of the seedpoint (if not given uses function getpts)

% t : maximum intensity distance (defaults to 0.2)

%

% The region is iteratively grown by comparing all unallocated neighbouring pixels to the region. 

% The difference between a pixel's intensity value and the region's mean, 

% is used as a measure of similarity. The pixel with the smallest difference 

% measured this way is allocated to the respective region. 

% This process stops when the intensity difference between region mean and

% new pixel become larger than a certain treshold (t)

%

% Example:

%

% I = im2double(imread('medtest.png'));

% x=198; y=359;

% J = regiongrowing(I,x,y,0.2); 

% figure, imshow(I+J);

%

% Author: D. Kroon, University of Twente

if(exist('reg_maxdist','var')==0), reg_maxdist=0.2; end

if(exist('y','var')==0), figure, imshow(I,[]); [y,x]=getpts; y=round(y(1)); x=round(x(1)); end

J = zeros(size(I)); % Output 

Isizes = size(I); % Dimensions of input image

reg_mean = I(x,y); % The mean of the segmented region

reg_size = 1; % Number of pixels in region

% Free memory to store neighbours of the (segmented) region

neg_free = 10000; neg_pos=0;

neg_list = zeros(neg_free,3); 

pixdist=0; % Distance of the region newest pixel to the regio mean

% Neighbor locations (footprint)

neigb=[-1 0; 1 0; 0 -1;0 1];

% Start regiogrowing until distance between regio and posible new pixels become

% higher than a certain treshold

while(pixdist<reg_maxdist&&reg_size<numel(I))

    % Add new neighbors pixels

    for j=1:4,

        % Calculate the neighbour coordinate

        xn = x +neigb(j,1); yn = y +neigb(j,2);

        % Check if neighbour is inside or outside the image

        ins=(xn>=1)&&(yn>=1)&&(xn<=Isizes(1))&&(yn<=Isizes(2));

        % Add neighbor if inside and not already part of the segmented area

        if(ins&&(J(xn,yn)==0)) 

                neg_pos = neg_pos+1;

                neg_list(neg_pos,:) = [xn yn I(xn,yn)]; J(xn,yn)=1;

        end

    end

    % Add a new block of free memory

    if(neg_pos+10>neg_free), neg_free=neg_free+10000; neg_list((neg_pos+1):neg_free,:)=0; end

    % Add pixel with intensity nearest to the mean of the region, to the region

    dist = abs(neg_list(1:neg_pos,3)-reg_mean);

    [pixdist, index] = min(dist);

    J(x,y)=2; reg_size=reg_size+1;

    % Calculate the new mean of the region

    reg_mean= (reg_mean*reg_size + neg_list(index,3))/(reg_size+1);

    % Save the x and y coordinates of the pixel (for the neighbour add proccess)

    x = neg_list(index,1); y = neg_list(index,2);

    % Remove the pixel from the neighbour (check) list

    neg_list(index,:)=neg_list(neg_pos,:); neg_pos=neg_pos-1;

end

% Return the segmented area as logical matrix

J=J>1;