{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "686e3eeb",
   "metadata": {},
   "source": [
    "# FITS_tutorial1\n",
    "Open a FITS file and retrieve the first plane of the image array\n",
    "as a TImage object\n",
    "\n",
    "\n",
    "\n",
    "\n",
    "**Author:** Claudi Martinez  \n",
    "<i><small>This notebook tutorial was automatically generated with <a href= \"https://github.com/root-project/root/blob/master/documentation/doxygen/converttonotebook.py\">ROOTBOOK-izer</a> from the macro found in the ROOT repository  on Tuesday, May 19, 2026 at 08:13 PM.</small></i>"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "6cea9a05",
   "metadata": {},
   "source": [
    "Here we open a FITS file that contains only the primary HDU, consisting on an image.\n",
    "The object you will see is a snapshot of the NGC7662 nebula,\n",
    "which was taken by the author on November 2009 in Barcelona."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "22220430",
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "TString dir = gROOT->GetTutorialDir();"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "5f01a70e",
   "metadata": {},
   "source": [
    "Open primary HDU from file"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "3a60f45b",
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "TFITSHDU hdu(dir + \"/io/fitsio/sample1.fits\");"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "5bc8d020",
   "metadata": {},
   "source": [
    "Dump the HDUs within the FITS file\n",
    "and also their metadata\n",
    "printf(\"Press ENTER to see summary of all data stored in the file:\"); getchar();"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "3f64c954",
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "hdu.Print(\"F+\");"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "0c2423ec",
   "metadata": {},
   "source": [
    "Here we get the exposure time."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "278de740",
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "printf(\"Exposure time = %s\\n\", hdu.GetKeywordValue(\"EXPTIME\").Data());"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a8b90d81",
   "metadata": {},
   "source": [
    "Read the primary array as a matrix, selecting only layer 0.\n",
    "This function may be useful to do image processing, e.g. custom filtering"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "658166d0",
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "std::unique_ptr<TMatrixD> mat(hdu.ReadAsMatrix(0));\n",
    "mat->Print();"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9926667f",
   "metadata": {},
   "source": [
    "Read the primary array as an image, selecting only layer 0."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "4ddd8e1b",
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "TImage * im = (TImage *)hdu.ReadAsImage(0);"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "79ff2984",
   "metadata": {},
   "source": [
    "Read the primary array as a histogram. Depending on array dimensions, the returned\n",
    "histogram will be 1D, 2D or 3D."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "740637f9",
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "TH1 * hist = (TH1 *)hdu.ReadAsHistogram();\n",
    "\n",
    "auto c = new TCanvas(\"c1\", \"FITS tutorial #1\", 1400, 800);\n",
    "c->Divide(2, 1);\n",
    "c->cd(1);\n",
    "im->Draw();\n",
    "c->cd(2);\n",
    "hist->Draw(\"COL\");"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "423b3dda",
   "metadata": {},
   "source": [
    "Draw all canvases "
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "e3aacd8f",
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "gROOT->GetListOfCanvases()->Draw()"
   ]
  }
 ],
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