A “Perceptual” colormap explicitly identifies a fixed value in the data
On geographical plot this fixed point can, for instance, the "sea level". A perceptual colormap provides a monotonic luminance variations above and below this fixed value. Unlike the rainbow colormap, this colormap provides a faithful representation of the structures in the data.
This macro demonstrates how to produce the perceptual colormap shown on the figure 2 in this article.
The function Perceptual_Colormap
takes two parameters as input:
h
, the TH2D
to be drawnval_cut
, the Z value defining the "sea level"Having these parameters this function defines two color maps: one above val_cut
and one
below.
Author: Olivier Couet
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Wednesday, April 17, 2024 at 11:11 AM.
Definition of a helper function:
%%cpp -d
void Perceptual_Colormap(TH2D *h, Double_t val_cut) {
Double_t max = h->GetMaximum(); // Histogram's maximum
Double_t min = h->GetMinimum(); // Histogram's minimum
Double_t per_cut = (val_cut-min)/(max-min); // normalized value of val_cut
Double_t eps = (max-min)*0.00001; // epsilon
// Definition of the two palettes below and above val_cut
const Int_t Number = 4;
Double_t Red[Number] = { 0.11, 0.19 , 0.30, 0.89};
Double_t Green[Number] = { 0.03, 0.304, 0.60, 0.91};
Double_t Blue[Number] = { 0.18, 0.827, 0.50, 0.70};
Double_t Stops[Number] = { 0., per_cut, per_cut+eps, 1. };
Int_t nb= 256;
h->SetContour(nb);
TColor::CreateGradientColorTable(Number,Stops,Red,Green,Blue,nb);
// Histogram drawing
h->Draw("colz");
}
TH2D *h = new TH2D("h","Perceptual Colormap",200,-4,4,200,-4,4);
h->SetStats(0);
Double_t a,b;
for (Int_t i=0;i<1000000;i++) {
gRandom->Rannor(a,b);
h->Fill(a-1.5,b-1.5,0.1);
h->Fill(a+2.,b-3.,0.07);
h->Fill(a-3.,b+3.,0.05);
gRandom->Rannor(a,b);
h->Fill(a+1.5,b+1.5,-0.08);
}
Perceptual_Colormap(h, 0.);
Info in <TCanvas::MakeDefCanvas>: created default TCanvas with name c1
Draw all canvases
gROOT->GetListOfCanvases()->Draw()