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   "cell_type": "markdown",
   "id": "coral-wright",
   "metadata": {},
   "source": [
    "# Source : from FITS images\n",
    "\n",
    "We can use a FITS image as the Source object for a ScopeSim Simulation\n",
    "\n",
    "**Warning: The simulation output is only as good as the input**\n",
    "   \n",
    "   If the pixel scale of the input (`CDELTn`) is bigger than the pixel scale of the instrument, ScopeSim will simply interpolate the image.\n",
    "   \n",
    "   Please don't expect wonders if the input image WCS information is not appropriate for the instrument you are using.\n",
    "   \n",
    "ScopeSim Source objects can be generated from fits.ImageHDU object in the following ways:  \n",
    "  \n",
    "1. Just an Image and scaling flux value  \n",
    "2. An Image and the associated synphot Spectrum\n",
    "3. An Image and arrays for wavelength and flux\n",
    "  \n",
    "- ``image_hdu=<fits.ImageHDU>`` + ``flux=<astropy.Quantity>``\n",
    "- ``image_hdu=<fits.ImageHDU>`` + ``spectra=<list of synphot.SourceSpectrum>``\n",
    "- ``image_hdu=<fits.ImageHDU>`` + ``lam=<array>`` + ``spectra=<list of arrays>``\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "armed-tampa",
   "metadata": {},
   "outputs": [],
   "source": [
    "import numpy as np\n",
    "import scipy\n",
    "import astropy.io.fits as fits\n",
    "from astropy import units as u\n",
    "import matplotlib.pyplot as plt\n",
    "%matplotlib inline\n",
    "\n",
    "import scopesim\n",
    "\n",
    "# Make an ImageHDU with some pixel data\n",
    "hdu = fits.ImageHDU(data=scipy.misc.face(gray=True))\n",
    "\n",
    "# Give the header some proper WCS info\n",
    "hdu.header.update({\"CDELT1\": 1, \"CUNIT1\": \"arcsec\", \"CRPIX1\": 0, \"CRVAL1\": 0,\n",
    "                   \"CDELT2\": 1, \"CUNIT2\": \"arcsec\", \"CRPIX2\": 0, \"CRVAL2\": 0,})\n",
    "\n",
    "\n",
    "# plotting function for later\n",
    "def plot(src):\n",
    "    plt.figure(figsize=(12, 5))\n",
    "    plt.subplot(121)\n",
    "    wave = range(3000, 25000)\n",
    "    plt.plot(wave, image_source.spectra[0](wave))\n",
    "    plt.xlabel(\"Wavelength [Angstrom]\")\n",
    "    plt.ylabel(\"Flux [ph/s/cm2/Angstrom]\")\n",
    "    plt.subplot(122)\n",
    "    plt.imshow(image_source.fields[0].data)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "abstract-medication",
   "metadata": {},
   "source": [
    "## 1. Just an Image and scaling flux value \n",
    "\n",
    "``image_hdu=<fits.ImageHDU>`` + ``flux=<astropy.Quantity>``\n",
    "\n",
    "It is assumed that the flux definied here is **integrated** flux and is the total flux contained in the image.\n",
    "\n",
    "**Note: In future version, header keywords like `BUNIT` etc will also be accepted. This functionality is not yet implemented though (April 2022).**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "viral-holly",
   "metadata": {},
   "outputs": [],
   "source": [
    "image_source = scopesim.Source(image_hdu=hdu, flux=10*u.ABmag)\n",
    "\n",
    "plot(image_source)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "agreed-stock",
   "metadata": {},
   "source": [
    "## 2. An Image and the associated synphot Spectrum\n",
    "\n",
    "``image_hdu=<fits.ImageHDU>`` + ``spectra=<list of synphot.SourceSpectrum>``\n",
    "\n",
    "In this case, the image pixel values are seen as multipiers for the spectrum at a given coordinate.\n",
    "\n",
    "**Note: It is the users responsibility to make sure the total flux of the \"cube\" (image * spectrum) is scaled appropriately.**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "moral-messaging",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Alternatively, see the SpeXtra and Pyckles libraries for more spectra\n",
    "vega_spec = scopesim.source.source_templates.vega_spectrum(mag=20)\n",
    "\n",
    "image_source = scopesim.Source(image_hdu=hdu, spectra=[vega_spec])\n",
    "\n",
    "plot(image_source)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "convinced-biography",
   "metadata": {},
   "source": [
    "## 3. An Image and arrays for wavelength and flux\n",
    "\n",
    "``image_hdu=<fits.ImageHDU>`` + ``lam=<array>`` + ``spectra=<array of arrays>``"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "center-latex",
   "metadata": {},
   "outputs": [],
   "source": [
    "n = 100\n",
    "wavelengths = np.geomspace(0.3, 2.5, n) * u.um\n",
    "flux = np.ones(n)\n",
    "\n",
    "image_source = scopesim.Source(image_hdu=hdu, lam=wavelengths, spectra=np.array([flux]))\n",
    "\n",
    "plot(image_source)"
   ]
  }
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