>Can anybody chime in regarding the resolution limit (640x64)
Light exposure on the sensor, the faster the frame rate, the darker the image as its a fixed aperture. Photographic buffs could explain it better, but my take is the faster the exposure the bigger the aperture that is needed to let more light in to make the photo look well lit. I don't know if parts of the sensor also work faster due to its circuit design but I would imagine this is also a factor just like its possible to read more data form the outside of a spin disk than the tracks close to the centre.
Light exposure on the sensor, the faster the frame rate, the darker the image as its a fixed aperture. Photographic buffs could explain it better, but my take is the faster the exposure the bigger the aperture that is needed to let more light in to make the photo look well lit. I don't know if parts of the sensor also work faster due to its circuit design but I would imagine this is also a factor just like its possible to read more data form the outside of a spin disk than the tracks close to the centre.