I have a simple fix for this, but the larger problem is that offscreen images do not follow the same assumptions as the norns screen (ARGB32 with the color planes all equal and quantized to 16 levels) so peek()-ing generically would require that peek() create a processed bitmap to return that matches format assumptions, or else provide an additional API to get the image format of the offscreen buffer.
I have a simple fix for this, but the larger problem is that offscreen images do not follow the same assumptions as the norns screen (ARGB32 with the color planes all equal and quantized to 16 levels) so peek()-ing generically would require that peek() create a processed bitmap to return that matches format assumptions, or else provide an additional API to get the image format of the offscreen buffer.