Include more info about working with contours

Some readme examples for using functions on a Contours object
Examples detecting and playing with simple shapes and contours

README.md

@@ -129,6 +129,39 @@ Also:
         mat.drawContour
         mat.drawAllContours
 
+### Using Contours
+
+`findContours` returns a `Contours` collection object, not a native array. This object provides
+functions for accessing, computing with, and altering the contours contained in it.
+See [relevant source code](src/Contours.cc) and [examples](examples/)
+
+        var contours = im.findContours;
+
+        # Count of contours in the Contours object
+        contours.size();
+
+        # Count of corners(verticies) of contour `index`
+        contours.cornerCount(index);
+
+        # Access vertex data of contours
+        for(var c = 0; c < contours.size(); ++c) {
+          console.log("Contour " + c);
+          for(var i = 0; i < contours.cornerCount(c); ++i) {
+            var point = contours.point(c, i);
+            console.log("(" + point.x + "," + point.y + ")");"
+          }
+        }
+
+        # Computations of contour `index`
+        contours.area(index);
+        contours.arcLength(index, isClosed);
+        contours.boundingRect(index);
+        contours.minAreaRect(index);
+        contours.isConvex(index);
+
+        # Destructively alter contour `index`
+        contours.approxPolyDP(index, epsilon, isClosed);
+        contours.convexHull(index, clockwise);
 
 ## MIT License
 The library is distributed under the MIT License - if for some reason that 

examples/detect-shapes.js

@@ -0,0 +1,52 @@
+#!/usr/bin/env node
+
+//
+// Detects triangles and quadrilaterals
+//
+
+var cv = require('../lib/opencv');
+
+var lowThresh = 0;
+var highThresh = 100;
+var nIters = 2;
+var minArea = 2000;
+
+var BLUE = [0, 255, 0]; //B, G, R
+var RED   = [0, 0, 255]; //B, G, R
+var GREEN = [0, 255, 0]; //B, G, R
+var WHITE = [255, 255, 255]; //B, G, R
+
+
+cv.readImage('./shapes.jpg', function(err, im) {
+
+	var out = new cv.Matrix(im.height(), im.width());
+
+	im.convertGrayscale();
+	im_canny = im.copy();
+
+	im_canny.canny(lowThresh, highThresh);
+	im_canny.dilate(nIters);
+
+	contours = im_canny.findContours();
+
+	for(i = 0; i < contours.size(); i++) {
+
+		if(contours.area(i) < minArea) continue;
+
+		var arcLength = contours.arcLength(i, true);
+		contours.approxPolyDP(i, 0.01 * arcLength, true);
+
+		switch(contours.cornerCount(i)) {
+		case 3:
+			out.drawContour(contours, i, GREEN);
+			break;
+		case 4:
+			out.drawContour(contours, i, RED);
+			break;
+		default:
+			out.drawContour(contours, i, WHITE);
+		}
+	}
+
+	out.save('./out.png');
+});

examples/quad-crosses.js

@@ -0,0 +1,55 @@
+#!/usr/bin/env node
+
+//
+// Finds quadrilaterals and fills them with an X
+//
+
+var cv = require('../lib/opencv');
+
+var lowThresh = 0;
+var highThresh = 100;
+var nIters = 2;
+var minArea = 2000;
+var maxArea = 100000;
+
+var BLUE = [0, 255, 0]; //B, G, R
+var RED   = [0, 0, 255]; //B, G, R
+var GREEN = [0, 255, 0]; //B, G, R
+var WHITE = [255, 255, 255]; //B, G, R
+
+
+cv.readImage('./quads.jpg', function(err, im) {
+
+	var out = im.copy();
+
+	im.convertGrayscale();
+	im_canny = im.copy();
+
+	im_canny.canny(lowThresh, highThresh);
+	im_canny.dilate(nIters);
+
+	contours = im_canny.findContours();
+
+	for(i = 0; i < contours.size(); i++) {
+
+		var area = contours.area(i);
+		if(area < minArea || area > maxArea) continue;
+
+		var arcLength = contours.arcLength(i, true);
+		contours.approxPolyDP(i, 0.01 * arcLength, true);
+
+		if(contours.cornerCount(i) != 4) continue;
+
+		var points = [
+			contours.point(i, 0),
+			contours.point(i, 1),
+			contours.point(i, 2),
+			contours.point(i, 3)
+		]
+
+		out.line([points[0].x,points[0].y], [points[2].x, points[2].y], RED);
+		out.line([points[1].x,points[1].y], [points[3].x, points[3].y], RED);
+	}
+
+	out.save('./out.png');
+});