Consider adding a 2D interactor
If an image is 2D, it can be useful to have a 2D interactor (I'm thinking of DXF or medical images).
And tbh, if we implement it, then it makes sense to supports JPG/PNG/TIFF/HDR/TGA/... too since it is basically free.
I know this is not the main purpose of f3d but since f3d is GPU accelerated, it may outperform other image previewers with large images.