For Protogenes see in brief OCD4 s.v.; more fully (e.g.) J.J. Pollitt, The Art of Ancient Greece: sources and documents (Cambridge 1990) 171-3 and passim.
[1] An alternative tradition (Pliny, Plutarch: see n.3) said Kaunos, which is near Lykia but actually in Karia.
[2] Given the other sources on the episode (see n.3) there seems to be something wrong with the text here. Bernhardy postulated a lacuna; Leopardi took the direct route and emended "Dionysos" to "Ialysos".
[3] An absurd figure, but otherwise this is recognizably the episode mentioned by the two principal sources on Protogenes: Pliny, Natural History 35.101-6, and Plutarch, Life of Demetrios 22. King Demetrios Poliorketes famously besieged Rhodes in 305/4 BCE (i.e. c.one full year, not two). At the time Protogenes was there, working on his painting of Ialysos, the eponymous hero of the Rhodian city of that name. Both writers assert, with variations of detail, that Demetrios was reluctant to do anything to damage either picture or artist; and Pliny goes as far as to identify this aesthetically-driven act of restraint (cf. Alexander the Great and the house of Pindar in Thebes) as the reason why the siege failed.