segmentation algorithm by region growth

Hi I need to complete the following assignement and im having issues. For a reason I don't understand my code is currently drawing the backgroup instead of the region i clicked on..

here is what i need to do : The goal of this practical work is to develop a semi-automatic segmentation algorithm by region growth of a medical image and to extract anatomical measurements of the segmented region.

I have attached a video of what my code should be doing and the image im working with.

img = imread('images\vertebre.png');

imshow(img);
[x, y] = ginput(1);

x = uint16(x);
y = uint16(y);

imgf = medfilt2(img, [7 7]);
imshow(imgf);
elemd2 = strel('disk', 2, 0);
seg = zeros(510,628,'logical');
seg(y,x)=1 ;
seg_precedent = zeros(510,628,'logical');
dispMat = zeros(size(img));

while (~isequal(seg, seg_precedent))
    seg_precedent = seg;
    intensite_region =  sum(seg(:) == 1);
    m_region = mean(intensite_region);
    std_region = std(intensite_region);
    seg_dilate = imdilate(seg, elemd2);
    contour = seg - seg_dilate;
    ind = find(contour==1);
    delta = 12;
    binf = m_region - (std_region + delta);
    bsup = m_region + (std_region + delta);
    contour =  seg_dilate - seg;
    inf_seg = binf < imgf;
    sup_seg = imgf < bsup;
    candidats = inf_seg &  sup_seg;
    seg = candidats;
    dispMat = img;
    dispMat(seg) = 0;
    RGB = cat(3,uint8(seg)*255+dispMat,dispMat,dispMat);
    imshow(RGB, [])
    drawnow
end

[Image Analyst]

What about simply thresholding?

[Julien Roussel]

Actually i have to do it this way... im pretty sure my problem is with this line :

intensite_region = sum(seg(:) == 1);

here what i was told about this line

using the seg variable as a mask, extract all of the elements from imgf that belong to the segmented region in seg (meaning all that elements equal to 1 in seg)