[Rivet] Problem executing rivet-mkhtml on MACBook Pro

[MICHELE GROSSI]

Dear Rivet Team,
I have a problem executing a bash script with the following output:

ERROR: required program 'convert' (for PNG output) could not be found.
Exiting..

The Macro is:
#! /bin/sh


rivet-mkhtml \
  VBFNLO/VBFNLO-NLO.yoda\
:"Title=NLO"\
:"ErrorBands=1"\
:"ErrorBandColor=red"\
:"RatioPlotErrorBandColor=red"\
:"ErrorBandOpacity=0.3"\
  Powheg/Powheg.yoda\
:"Title=Powheg+Pythia 8"\
:"LineColor=green"\
:"ErrorBands=1"\
:"ErrorBandColor=green"\
:"RatioPlotErrorBandColor=green"\
:"ErrorBandOpacity=0.3"\
  VBFNLO/Herwig-MCatNLO-DipoleShower.yoda\
:"Title=VBFNLO 3+Herwig 7"\
:"LineColor=brown"\
:"ErrorBands=1"\
:"ErrorBandColor=brown"\
:"RatioPlotErrorBandColor=brown"\
:"ErrorBandOpacity=0.3"\
  Powheg/lhef.yoda\
:"Title=Powheg-lhef"\
:"LineColor=blue"\
:"ErrorBands=1"\
:"ErrorBandColor=blue"\
:"RatioPlotErrorBandColor=blue"\
:"ErrorBandOpacity=0.3"\

Can you kindly help me?
Thank you in advance
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