ML-Kurs-SS2023/notebooks/01_intro_ex_1a_sol.ipynb

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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Exercise 1: Create numpy array and draw rgb color objects"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import numpy as np\n",
    "import matplotlib.pyplot as plt"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "create data array 2x2 as pixel position and 1x3 as rgb color data"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "width, height = 200, 200\n",
    "data = np.zeros((height, width, 3), dtype=np.uint8)\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "draw blue cross"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "x =  np.arange(width)\n",
    "x_1 = np.arange(width)\n",
    "x_2 = np.arange(width-1,-1,-1)\n",
    "y = np.arange(height)\n",
    "data[x_1,y] = [0,0,255]\n",
    "data[x_2,y] = [0,0,255]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    " draw a square "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "lower = 55\n",
    "upper = 75\n",
    "data[lower:upper,lower:upper] = [0,255,0]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "create a mask of a circle using indexing\n",
    "np.newaxis adds another dimension\n",
    "we create a row and column vector and fill it using the condition"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "x_center = 100\n",
    "y_center = 100\n",
    "radius = 10\n",
    "mask = (x[np.newaxis,:]-x_center)**2 + (y[:,np.newaxis]-y_center)**2 < radius**2\n",
    "data[mask] = [255,0,0]\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# plot image\n",
    "plt.figure(figsize=(4.,4.),dpi=100,facecolor='lightgrey')\n",
    "plt.imshow(data)\n",
    "plt.show()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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