Forget the histogram. For that matter, forget imaging until you have mastered visual observation. For a beginner I would recommend going to the GONG H-alpha Network:
If there are any filaments on these images, try to observe them and tune to get them to be as dark as possible - then you are on band, and any prominences that are on the limb should then be visible as well. Seeing prominences is good, and you are near to on-band if you can currently see them. Be patient - solar minimum is a difficult time to cut your H alpha teeth...
Some granulations can be seen in white light, but, are better seen in H-Alpha.
What you are referring to as "granulations" are not the underlying convection cells of the photosphere (which would be very subtle at best - e.g. "invisible" - and would require excellent seeing with a hi-res single stack filter system so you can see them from the parasitic continuum leakage coming through the chromosphere lying above: http://www.astrosurf...-contrast-2.htm ). They are indeed more easily observed in white-light continuum (especially near the limb), if not narrow band non-H alpha wavelengths such as the G-band, CaK, etc:
The website you cite is completely erroneous in this instance for nomenclature. Instead, you are seeing what is referred to as the "chromospheric network" of spicules, mottles, fibrils, plage, and other features of the chromosphere:
Edited by BYoesle, 08 August 2018 - 06:34 AM.