Filling blobs (shapes) with unique colors based on area

Question

I have some shapes on an image that i've attempted to label according to their Area using a solution provided to me:

stats = regionprops(BW,'Area')
stats2 = regionprops(BW,'Centroid')

figure,imshow(BW)
for k = 1:numel(stats)
    xy = stats2(k).Centroid
    if (stats(k).Area>TH)
        text(xy(1),xy(2),'L') %// Large Shape
    else
        text(xy(1),xy(2),'S') %// Small Shape
    end
end

But it turns out the shapes are too small for the letters ( which would be too small even if I changed the font), I'm wondering if there's a way to do the thresholding to produce a colour code i.e change the filling of the shapes based on their area?

Answer 1

See if this is inspiring enough for you -

%// Input image. This one is chosen as it is available in MATLAB image library
img = imread('coins.png'); 

%// Convert to binary image
BW = im2bw(img,0.4); %// 0.4 as binary thresehold worked for this specific image

%// Get area and pixel-list stats
stats = regionprops(BW,'Area');
stats2 = regionprops(BW,'PixelIdxList');

s1 = struct2array(stats);
[v1,v2,v3] = unique(s1);
num_colors = numel(v1);

%// Pixel values per channel for creating color codes
pix_per_ch = linspace(0,255,ceil(power(num_colors,1/3)));

%// Unique 3 color codes
all_color_codes = allcomb(pix_per_ch,pix_per_ch,pix_per_ch);
%// allcomb is a MATLAB File-exchange tool avaiialble at -
%// http://www.mathworks.in/matlabcentral/fileexchange/10064-allcomb

%// Unique 3 color codes for the number of shapes available
color_codes = all_color_codes(randi(size(all_color_codes,1),num_colors,1),:);

%// Sort these uniques colors based on their grayscale intensities
[~,ind]=sort(rgb2gray(uint8(permute(color_codes,[1 3 2]))));
sorted_color_codes = color_codes(ind,:);

%// Pre-allocate for the ouput image
out = uint8(255.*BW(:,:,ones(1,3)));

%// Assign each shape a unique color based on their areas
for k = 1:numel(stats)
    ind1 = stats2(k).PixelIdxList;
    indx = bsxfun(@plus,ind1,[0:2].*size(img,1)*size(img,2));
    color_code = sorted_color_codes(v3(k),:);
    color_code_ext = color_code(ones(1,numel(ind1)),:);
    out(indx) = color_code_ext;
end

%// Display input, output results
figure,
subplot(211),imshow(img),
title('Input Image')
subplot(212),imshow(out),
title('Output Image (Brighter colors represent larger shapes)')

Output -