Lecture 2.4 - Reading, writing and displaying images.ipynb

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    "## Hi and welcome to your first code along lesson!\n",
    "\n",
    "#### Reading, writing and displaying images with OpenCV"
   ]
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   "source": [
    "Let's start by importing the OpenCV libary "
   ]
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   "source": [
    "# Press CTRL + ENTER to run this line\n",
    "# You should see an * between the [ ] on the left\n",
    "# OpenCV takes a couple seconds to import the first time\n",
    "\n",
    "import cv2"
   ]
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    "# Now let's import numpy\n",
    "# We use as np, so that everything we call on numpy, we can type np instead\n",
    "# It's short and looks neater\n",
    "\n",
    "import numpy as np "
   ]
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   "source": [
    "Let's now load our first image"
   ]
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    "# We don't need to do this again, but it's a good habit\n",
    "import cv2 \n",
    "\n",
    "# Load an image using 'imread' specifying the path to image\n",
    "input = cv2.imread('./images/input.jpg')\n",
    "\n",
    "# Our file 'input.jpg' is now loaded and stored in python \n",
    "# as a varaible we named 'image'\n",
    "\n",
    "# To display our image variable, we use 'imshow'\n",
    "# The first parameter will be title shown on image window\n",
    "# The second parameter is the image varialbe\n",
    "cv2.imshow('Hello World', input)\n",
    "\n",
    "# 'waitKey' allows us to input information when a image window is open\n",
    "# By leaving it blank it just waits for anykey to be pressed before \n",
    "# continuing. By placing numbers (except 0), we can specify a delay for\n",
    "# how long you keep the window open (time is in milliseconds here)\n",
    "cv2.waitKey()\n",
    "\n",
    "# This closes all open windows \n",
    "# Failure to place this will cause your program to hang\n",
    "cv2.destroyAllWindows()"
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    "# Same as above without the extraneous comments\n",
    "\n",
    "import cv2 \n",
    "\n",
    "input = cv2.imread('./images/input.jpg')\n",
    "\n",
    "cv2.imshow('Hello World', input)\n",
    "cv2.waitKey(0)\n",
    "cv2.destroyAllWindows()"
   ]
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   "source": [
    "### Let's take a closer look at how images are stored"
   ]
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   "source": [
    "# Import numpy\n",
    "import numpy as np"
   ]
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     "text": [
      "(830L, 1245L, 3L)\n"
     ]
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   "source": [
    "print input.shape"
   ]
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   "source": [
    "#### Shape gives the dimensions of the image array\n",
    "\n",
    "The 2D dimensions are 830 pixels in high bv 1245 pixels wide.\n",
    "The '3L' means that there are 3 other components (RGB) that make up this image."
   ]
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     "text": [
      "Height of Image: 830 pixels\n",
      "Width of Image:  1245 pixels\n",
      "No of RGB elements:  3 values\n"
     ]
    }
   ],
   "source": [
    "# Let's print each dimension of the image\n",
    "\n",
    "print 'Height of Image:', int(input.shape[0]), 'pixels'\n",
    "print 'Width of Image: ', int(input.shape[1]), 'pixels'\n",
    "print 'No of RGB elements: ', int(input.shape[2]), 'values'"
   ]
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   "source": [
    "### How do we save images we edit in OpenCV?"
   ]
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    "# Simply use 'imwrite' specificing the file name and the image to be saved\n",
    "cv2.imwrite('output.jpg', input)\n",
    "cv2.imwrite('output.png', input)"
   ]
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