I’m posting this into the forum, these are Richard’s comments - we were still kind of figuring out the appropriate place for discussions and I think gitlab ain’t it so let’s try it here.
This discussion is in reference to:
@rbowman’s comments on the first version of the spinning-mask idea
I think this is potentially a really nice way to produce a single pixel imager. The most common way is to use a DLP chip (essentially a hacked micro projector, though most folk use the TI development board for convenience). This has impressive specs: patterns display at up to 1.4kHz or even 20kHz (depending on budget), timing is really good, and the masks can be arbitrary. However, it costs from £400 up to £20k, which is a bit steep for many applications!
Using a spinning disk has, to my mind, advantages and disadvantages. Good news first:
- Spinning a disk quickly is easy - can potentially get a very high pattern rate.
- Can be pretty cheap.
- Patterns get translated across the image - might be able to use this to improve resolution
- Patterns translate across the image - motion blur might be a problem for long exposures, or you’d have to stop the disk at each position (tricky to go fast).
- You’d need to encode the position of the disk very precisely, and account for any wobble in the rotation axis. I think that could be done though.
I am also not sure if simply rotating a mask about its centre would be able to give (enough) independent patterns; it constrains you to have some symmetry between all the patterns, which could be a problem. That can be simulated, though. I’d always assumed we’d use a strip near the edge - which also simplifies the optical design.
Lastly, bear in mind that the optical design needs to have an imaging system between the object and the mask - the one that’s shown in the PDF would work, but only as a pinhole camera - the efficiency would be frighteningly low. Using a lens in front of the mask to image the scene onto the mask should work much better…