Empty bins in surf2 plot option

ROOT
1

Hi everybody!
I have a 2D histogram with many empty bins. I would like them to appear white when using a rainbow colour palette. In the z scale I have positive and negative values.
If I use the colz option it is colz1, then I manage to make the empty bins appear white. But I would like to use the option surf2 to make maxima and minima more evident. Is there a way to plot the empty bins as white also in this case ?

Thanks

Andrea

2

In case of surface plot you cannot do that with an option. What you can do if to define your own palette with some specific color (white) at 0.

3

Thanks for the answer. Is there a tutorial on how to change the Palette ? I was trying this code:

UInt_t Number = 3;
Double_t Red[3] = { 0.00, 0.00, 1.00};
Double_t Green[3] = { 0.00, 1.00, 0.00};
Double_t Blue[3] = { 1.00, 0.00, 1.00};
Double_t Length[3] = { 0.00, 0.50, 1.00 };
Int_t nb=50;
TColor::CreateGradientColorTable(Number,Length,Red,Green,Blue,nb);
h2->SetContour(nb);
h2->Draw(“surf1z”);

But I could not figure out how to put in white a range of the palette around 0…

4

Hi! I found
something that works to make the empty point white:

const UInt_t Number = 5;
Double_t Red[Number] = {1.00, 0.00, 1.00, 1.00, 0.00};
Double_t Green[Number] = { 0.00, 1.00, 1.00, 0.00, 0.00};
Double_t Blue[Number] = { 0.00, 0.00, 1.00, 1.00, 1.00};
Double_t Length[Number] = { 0.00, 0.48, 0.52, 0.55, 1.00 };
Int_t nb=50;

TColor::CreateGradientColorTable(Number,Length,Blue,Green,Red,nb);
h4->SetContour(nb);
// hcol2->SetMaximum(6000);
// hcol2->SetMinimum(-6000);
h4->Draw(“surf2”);

However, I cannot understand the meaning of the command Double_t Red[Number] = {1.00, 0.00, 1.00, 1.00, 0.00}; Am I defining 5 colours? From the class documentation I cannot understand…

5

Yes in that case you define the 5 colors for each oh them you specify the value of Red Green and Blue.
And the position (in % on the palette length (Length vector)). You need to figure out when the 0 is. That can easily computed with the Min and Max of the histogram. CreateGradientColorTable then bail the palette for you

root.cern.ch/doc/master/classTColor.html#C05