Image is 4K.
- Blender Render
- Ortho camera with perfectly matched plane
- Shadeless material
- All kinds of interpolation in texture settings are disabled
- Filter size is lowest possible
There is difference, even in full resolution:
Without Gamma node it is barely visible, but I am not sure which resolution will be final 4K or 1080P, so I put 50% of 4K in render settings. And at half-sized render original image is obviously sharper.
Full oversampling also doesn't do anything with that.