Persitifying Hex Colors

[quantiser]

I often use hexadecimal color codes and convert them to TColor using TColor::GetColor (const char *hexcolor) [1] for coloring TH1, TGraph, etc. However, when I store the histograms or graphs in a root file and try to draw them later, they appear invisible, i.e. the color is forgotten. How can I make sure that the color is also stored in the root file and used automatically?

ROOT Version: 6.14/09

[1] ROOT: TColor Class Reference

[couet]

Yes, colors are not stored in ROOT file. You should redefine them. Usually it is done in rootlogon.C.

[nmangane]

Is there a more flexible/portable/shareable/self-contained version of this? i.e. not sending everyone your rootlogon.C file so they can work with the same plots.

[couet]

Not really. The Colors are not stored on purpose. They might be a lot of them and we cannot afford storing them in the root file. Colors should be redefined.

[quantiser]

Thanks for the replies. If storing colors is not an option, could ROOT be updated to not make graphs/histograms invisible after storing to file?

[couet]

Invisible ? can you provide an example ?

[quantiser]

Sure.

Using ROOT 6.24/01, I make a histogram, create TColor from hex code, draw it (color works), and store it to a file.

root [0] TH1F h(“h”,“”,100,-5,5)
root [1] h.FillRandom(“gaus”,50000)
root [2] Int_t col = TColor::GetColor(“#c53a48”)
root [3] h.SetLineColor(col)
root [4] h.Draw(“hist”)
root [5] TFile f(“test_color_visibility.root”,“RECREATE”)
root [6] f.cd()
root [7] h.Write()
root [8] f.Close()

I close the ROOT session, start a new one, open the file, and draw the histogram: histogram is invisible.

HunterBidenLaptop@2019:~ root test_color_visibility.root
root [2] h->Draw(“hist”)

[couet]

with ROOT master (6.26) I get:

% root -l test_color_visibility.root
root [1] h->Draw()

[couet]

Indeed it depends if the color you get in the initial macro is defined (not white) or not.