Lecture 4.4 - Matching Contours Shape.ipynb

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    "## Shape Matching"
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    "**cv2.matchShapes(contour template, contour, method, method parameter)**\n",
    "\n",
    "**Output** – match value (lower values means a closer match)\n",
    "\n",
    "- Contour Template – This is our reference contour that we’re trying to find in the new image\n",
    "- Contour – The individual contour we are checking against\n",
    "- Method – Type of contour matching (1, 2, 3)\n",
    "- Method Parameter – leave alone as 0.0 (not fully utilized in python OpenCV)\n"
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      "0.168183165072\n",
      "0.199469102562\n",
      "0.189497606273\n",
      "0.111010582763\n"
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    "import cv2\n",
    "import numpy as np\n",
    "\n",
    "# Load the shape template or reference image\n",
    "template = cv2.imread('images/4star.jpg',0)\n",
    "cv2.imshow('Template', template)\n",
    "cv2.waitKey()\n",
    "\n",
    "# Load the target image with the shapes we're trying to match\n",
    "target = cv2.imread('images/shapestomatch.jpg')\n",
    "target_gray = cv2.cvtColor(target,cv2.COLOR_BGR2GRAY)\n",
    "\n",
    "# Threshold both images first before using cv2.findContours\n",
    "ret, thresh1 = cv2.threshold(template, 127, 255, 0)\n",
    "ret, thresh2 = cv2.threshold(target_gray, 127, 255, 0)\n",
    "\n",
    "# Find contours in template\n",
    "contours, hierarchy = cv2.findContours(thresh1, cv2.RETR_CCOMP, cv2.CHAIN_APPROX_SIMPLE)\n",
    "\n",
    "# We need to sort the contours by area so that we can remove the largest\n",
    "# contour which is the image outline\n",
    "sorted_contours = sorted(contours, key=cv2.contourArea, reverse=True)\n",
    "\n",
    "# We extract the second largest contour which will be our template contour\n",
    "template_contour = contours[1]\n",
    "\n",
    "# Extract contours from second target image\n",
    "contours, hierarchy = cv2.findContours(thresh2, cv2.RETR_CCOMP, cv2.CHAIN_APPROX_SIMPLE)\n",
    "\n",
    "for c in contours:\n",
    "    # Iterate through each contour in the target image and \n",
    "    # use cv2.matchShapes to compare contour shapes\n",
    "    match = cv2.matchShapes(template_contour, c, 1, 0.0)\n",
    "    print match\n",
    "    # If the match value is less than 0.15 we\n",
    "    if match < 0.15:\n",
    "        closest_contour = c\n",
    "    else:\n",
    "        closest_contour = [] \n",
    "                \n",
    "cv2.drawContours(target, [closest_contour], -1, (0,255,0), 3)\n",
    "cv2.imshow('Output', target)\n",
    "cv2.waitKey()\n",
    "cv2.destroyAllWindows()"
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    "http://docs.opencv.org/2.4/modules/imgproc/doc/structural_analysis_and_shape_descriptors.html"
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