Double_t transfer_function(Double_t *x, Double_t * /*param*/)
{
   //This function is required to suppress
   //boxes for empty bins - make them transparent.
   if (x)
      return *x > 0 ? 1. : 0.;
   
   return 0.;
}


void DoItThisWay(){

  gStyle->SetCanvasPreferGL(kTRUE);
  gStyle->SetPalette(1);


  TFile* file = new TFile("file.root","READ");

  TH3F* hist = (TH3F*) file->Get("hist");
  hist->SetName("hist");

  TCanvas* c1 = new TCanvas("c1","3D",600,600);
  hist->Draw("glcolz");


  TFile* file2 = new TFile("file2.root","RECREATE");
  hist->Write();
  file2->Close();
  
  TFile* file3 = new TFile("file2.root","READ");
  TH3F* hist2 = (TH3F*) file3->Get("hist");
  hist2->SetName("hist2");

   TList * lof = hist2->GetListOfFunctions();
   if (!lof) {
      std::cout<<"List of functions is null\n";
      delete hist2;
      return;
   }
   lof->Add(new TF1("TransferFunction", transfer_function, 0., 1000., 0));

  
  TCanvas* c2 = new TCanvas("c2","3D modified",600,600);
  hist2->Draw("glcolz");

  
  
}