Preprocessing

README.md

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+You'll need octave 3.8.1+ to run the included packages. They won't
+work on ohaton, since the server's missing some required libraries
+(well -- something's broken, I dunno).
+
+Run the the following once, since it will install the packages for
+you:
+
+> pkg install packages/*
+
+You can ensure it is all installed with:
+
+> pkg list
+

driver.m

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+function driver
+
+  pkg load image;
+
+  image = imread('smile.png');
+
+  preprocess(image);
+
+end

preprocess.m

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+function features = preprocess(image)
+  % PREPROCESS takes an image and produces a vector with
+  % found features
+
+  features = struct('width', {},
+		'height', {},
+		'pixels', {},
+		'midpoint', zeros(1,2),
+		'x', {},
+		'y', {});
+
+  % 1. Threshold the image
+  img = rgb2gray(image);
+  img = im2bw(img, graythresh(img));
+
+  % 2. Find boundaries
+  [B,L] = bwboundaries(img);
+
+  % 3. Extract features
+  for k=2:numel(B),
+    [features(k-1).width, features(k-1).height] = calcDim(B{k});
+    features(k-1).x = min(B{k}(:,1));
+    features(k-1).y = min(B{k}(:,2));
+    features(k-1).pixels = calcSize(B{k},L);
+    [features(k-1).midpoint(1), features(k-1).midpoint(2)] = calcMedian(B{k}, L);
+  endfor
+
+end
+
+function showImageBounds(img, B)
+  figure; imshow(img); hold on;
+  for k=2:numel(B),
+    plot (B{k}(:,2), B{k}(:,1), 'r', 'linewidth', 2);
+  endfor
+  hold off
+end
+
+function [width, height] = calcDim(bounds)
+  width = max(bounds(:,1))-min(bounds(:,1));
+  height = max(bounds(:,2))-min(bounds(:,2));
+end
+
+function pixels = calcSize(bounds, labels)
+  label = labels(bounds(1,1), bounds(1,2));
+  pixels = sum(sum(labels == label));
+end
+
+function [x,y] = calcMedian(bounds, labels)
+  label = labels(bounds(1,1), bounds(1,2));
+  y = findWeightCentre(sum(labels==label));
+  x = findWeightCentre(sum(labels'==label));
+end
+
+function index = findWeightCentre(array)
+   values = zeros(size(array));
+   for k=2:(length(array)-1),
+     values(k) = sum(array(1:k-1))-sum(array(k+1:end));
+   end
+  [tmp, index] = min(abs(values(2:end-1)));
+end