{
 "metadata": {
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  {
   "cells": [
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# setup\n",
      "%matplotlib inline"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "# Introduction: images are numpy arrays\n",
      "\n",
      "A grayscale image is just a 2D array:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "import numpy as np\n",
      "r = np.random.rand(500, 500)\n",
      "from matplotlib import pyplot as plt, cm\n",
      "plt.imshow(r, cmap=cm.gray, interpolation='nearest')"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Trying that with a real picture:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "from skimage import data\n",
      "coins = data.coins()\n",
      "print(type(coins))\n",
      "print(coins.dtype)\n",
      "print(coins.shape)\n",
      "plt.imshow(coins, cmap=cm.gray, interpolation='nearest')"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "A color image is a 3D array, where the last dimension has size 3 and represents the red, green, and blue channels:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "lena = data.lena()\n",
      "print(lena.shape)\n",
      "plt.imshow(lena, interpolation='nearest')"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "These are *just numpy arrays*. Making a red square is easy using just array slicing and manipulation:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "lena[100:200, 100:200, :] = [255, 0, 0] # [red, green, blue]\n",
      "plt.imshow(lena)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "As we will see, this opens up many lines of analysis for free.\n",
      "\n",
      "## Exercise: draw an H\n",
      "\n",
      "Define a function that takes as input an RGB image and a pair of coordinates (row, column), and returns the image (optionally a copy) with green letter H overlaid at those coordinates. The coordinates should point to the top-left corner of the H.\n",
      "\n",
      "The arms and strut of the H should have a width of 3 pixels, and the H itself should have a height of 24 pixels and width of 20 pixels."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def draw_h(image, coords, in_place=True):\n",
      "    pass # code goes here"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Test your function like so:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "lena_h = draw_h(lena, (50, -50), in_place=False)\n",
      "plt.imshow(lena_h)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "## Bonus points: RGB intensity plot\n",
      "\n",
      "Plot the intensity of each channel of the image along some row."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def plot_intensity(image, row):\n",
      "    pass # code goes here"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Test your function here:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "plot_intensity(coins, 50)\n",
      "plot_intensity(lena, 250)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    }
   ],
   "metadata": {}
  }
 ]
}