Well, of course people's expression vary considerably according their mood - we are not statues, it is obvious, isn't it ? So, taken this into account I just think that the "spirit" of the painting is very different from that of taking a photo. If you take a photo you catch the moment - it is a snapshot recording reality as it is exactly there, but if you are a painter and you have to make a portrait I guess you have to go beyond what you are seeing just in front of you and try to grasp the essence of what you have to portray... I believe portraits are not realistic because of this, firstly ! (And then yes, there were rules and conventions about how to portray people and oh, people liked to be painted in a certain way rather than others...)

I imagine Saint-Just very severe, but not as Hamel's "German priest" XD XD-> this portrait features a kind of empty coldness I don't feel appropriate to the subject ! I rather imagine him as a mix between Prudhon's portrait (who looks severe too, but in a different way - not only this, it's much more mysterious and nuanced) and David's, which I am personally not fond of, I believe it is very realistic, though (if you read Charles Nodier accounts of Saint-Just's physical appearence you will find something very similar to David's version !). And you ? How do you imagine him ?

Really a pity they didn't have photos !! I imagine a photo reportage of Danton's trial... *gg* :D