void read_TH2D(){

  TFile *f = new TFile("TH2D.root");
  TH2D *h2 = (TH2D*)f->Get("PDM");
  
  Int_t x, y;
  Float_t photons;
  for (x=0; x<48; x++) {
    cout<<"----------" <<endl;
    cout<<"new x" <<endl;
    for (y=0; y<48; y++) { 
      cout<<"new y" <<endl;
      photons = h2->GetBinContent(x,y);
      cout<<"bin("<<x <<"," <<y <<") = " <<photons <<endl;
      if(photons>0)
	cout<<"bin("<<x <<"," <<y <<") with content =! 0 " <<endl;
    }
  }
  h2->Draw();

}