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[hist] clip color to minimum if below with COLZ TH2 #19441

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[hist] clip color to minimum if below with COLZ TH2 #19441

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8b5da2f
[hist] clip color to minimum if below
ferdymercury Jul 23, 2025
5c0c142
[nfc][hist] improve documentation and example
ferdymercury Jul 23, 2025
3ce5822
[nfc] clarify condition
ferdymercury Jul 23, 2025
c460faf
[nfc] fix typo
ferdymercury Jul 25, 2025
ba7af67
[hist] fix TEXT with Logz use
ferdymercury Jul 25, 2025
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21 changes: 18 additions & 3 deletions hist/histpainter/src/THistPainter.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -1110,6 +1110,11 @@ painted with the color corresponding to the new maximum.
When the minimum of the histogram is set to a greater value than the real minimum,
the bins having a value between the real minimum and the new minimum are not drawn
unless the option `0` is set.
In other words, option `COLZ0` forces the painting of bins with content < set minimum with
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Why adding this note ? it repeats what is already said

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It does not specify that it depends on whether minimum is negative or positive, right?

a color corresponding to the set minimum. In contrast, option `COLZ` would not draw values
smaller than the specified minimum. Note that both `COLZ` and `COLZ0` still do not draw
empty bins, ie bins with `content == error == 0`, if the set min is not negative.
(Note that option `COLZ0` for TH2Poly has a different behavior than for TH2.)

The following example illustrates the option `0` combined with the option `COL`.

Expand All @@ -1129,11 +1134,18 @@ Begin_Macro(source)
hcol22->SetBit(TH1::kNoStats);
c1->cd(1); hcol21->Draw("COLZ");
c1->cd(2); hcol22->Draw("COLZ0");
hcol21->SetMaximum(100);
hcol21->SetMinimum(40);
hcol22->SetMaximum(100);
hcol22->SetMinimum(40);
}
End_Macro

Note that the behavior of `COLZ` is not symmetric: it does not draw values below the specified minimum,
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Same comment. The original doc says it already.

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I did not find specified in the original doc what happens with empty bins, nor what happens with values above maximum.

but does draw values above the specified maximum by clipping them to the maximum color. In contrast, `COLZ0`
clips color on both lower and upper sides. Both `COLZ0` and `COLZ` exclude drawing empty bins (`content == error == 0`),
if the set minimum is not negative.

\since **ROOT version 6.09/01:**

When the option SAME (or "SAMES") is used with the option COL, the boxes' color
Expand Down Expand Up @@ -2457,7 +2469,7 @@ the option "GLLEGO".
\since **ROOT version 6.09/01**

In some cases it can be useful to not draw the empty bins. the option "0"
combined with the option "COL" et COLZ allows to do that.
combined with the option "COL" and "COLZ" allows to do that.

Begin_Macro(source)
{
Expand Down Expand Up @@ -5903,7 +5915,7 @@ void THistPainter::PaintColorLevels(Option_t*)
}
}
} else {
color = Int_t(0.01+(z-zmin)*scale);
color = Hoption.Zero ? Int_t(0.01+(std::max(z, zmin)-zmin)*scale) : Int_t(0.01+(z-zmin)*scale);
}

Int_t theColor = Int_t((color+0.99)*Float_t(ncolors)/Float_t(ndivz));
Expand Down Expand Up @@ -10126,6 +10138,9 @@ void THistPainter::PaintText(Option_t *)

// 2D histograms
} else {
Double_t zmin = Hparam.zmin;
if (Hoption.Logz) zmin = TMath::Power(10,Hparam.zmin);

text.SetTextAlign(22);
if (Hoption.Text == 1) angle = 0;
text.SetTextAngle(angle);
Expand All @@ -10145,7 +10160,7 @@ void THistPainter::PaintText(Option_t *)
}
if (!IsInside(x,y)) continue;
z = fH->GetBinContent(bin);
if (z < Hparam.zmin || (z == 0 && !Hoption.MinimumZero)) continue;
if (z < zmin || (z == 0 && !Hoption.MinimumZero)) continue;
if (Hoption.Text>2000) {
e = fH->GetBinError(bin);
tf.Form("#splitline{%s%s}{#pm %s%s}",
Expand Down
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