Minor issues with a new plugin

[David_Tschumperle (G'MIC staff)]

@Philemo

If it weren’t the mere fact that most of the effects are actually working like a charm, I would think it’s because I send images coded with a value from 0 to 1 per channel and not 0 to 255.

That is certainly the cause of the issue. In G’MIC, RGB colors are expected to be in [0,255] (float-valued), so any color transformation formula assumes this range.