I am aware of what Bayer Drizzle is. PI supports it as well. Interpolation is avoided in bayer drizzle because it is still drizzling. It's just drizzling in a color-aware manner. I have tried DSS's drizzle features...however they seem to be very unstable. I was never able to drizzle full 5D III frames no matter what I did. To actually get it to work well, I usually had to choose an ROI less than 50% of the field, which was certainly not ideal. DSS is also 32-bit, and doesn't seem to implement LBA, so it would never use over 2GB of memory either, which limited the amount of information it would work with anyway. I don't know if DSS really has a superior implementation of bayer drizzle or not...given how basic DSS seems to be in general, I'm a bit skeptical. (Also, IIRC, DSS development has been abandoned, and it's definitely got some bugs that haven't been fixed in the last few years...and if development has been abandoned, it won't be updated to add compatibility for new DSLRs in years to come.)
I don't think it is really safe to say that you wouldn't have any difference with bayer drizzle vs. a mono sensor. The problem is the signal information from a bayer sensor is sparse. It does not have a truly full constituent of information across all the color channels. It IS possible to recover a lot of the missing information with drizzling, however, with bayer drizzle, you are effectively actually drizzling three images, not from data with a 100% fill factor...but from data with 50% and 25% fill factors.
You really need a LOT of subs to effectively recover enough information for bayer drizzle to work well because you have to fill in so much information, and with that many longer subs, information will still spread out more, same as with normal stacking of many, many subs. Resolution is favored by stacking carefully culled subs that only contain the best information/smallest stars...which is really easy to do when your mono LRGB subs can be 10-15s at a high gain setting.
Thing is, I am still undersampled with the ASI1600, at a 1.3"/px image scale. I can drizzle even that data fairly effectively...and improve resolution even more. FWHMs around 1.8-1.9". So even with drizzling, that can be employed with both types of cameras.
The pixels on the ASI1600 are about 1/3 the area of a 6D or 5D III, 1/10th the area of an A7s, a little over 1/2 the area of a D810's pixels. I've never seen a 50% FWHM improvement from any kind of drizzling... I do get some decent improvements...but I find it is a lot more useful for rounding up stars:
The low pass filter is really the primary issue. I always knew it was an issue, however I wasn't quite aware of how significant until I used the ASI1600. Even on a night of bad seeing, my FWHMs are still around 2.3" with the ASI....a night of average seeing and I would easily be 5-6" on the 5D III. In part I'm sure some of that blur is from seeing over longer subs, but with nights of excellent seeing my FWHMs never go much below 4"...about the best individual sub I might have seen was over 3.8".
If you really want a resolution benefit with a DSLR, I think one of the current generation APS-C cameras with an astro mod, to remove that darn low pass filter, is probably the best way to do it. However, you lose the large FoV, and an APS-C is marginally larger than 4/3...a 2x1 mosaic with a 4/3 sensor will produce a larger FoV.
Anyway. This is just the beginning of the mono cmos astro cam age. It won't be long before APS-C sized sensors, possibly even Sony Exmor Rs, find their way into one of these new cameras. We may even see a full frame Exmor sensor in one of them someday in the not so distant future. ZWO has a distinct mission to keep their equipment in the "affordable" range, which I think they have done a great job of so far...so I consider it all to be quite game changing. Outside of the rare individual who has easy access to a good dark site, I don't know if I can continue to recommend DSLRs to very many people...not even beginners...given how effective NB imaging can be with these modern CMOS cameras with very, very short exposures. Short enough to be done unguided on beginner-grade equipment. That is totally a game changer for city-bound beginners...with just the camera and a single Ha filter screwed directly into the 1.25" filter holder that comes with the camera, a beginner could get started with high quality data even in a white zone with an AVX and a fast refractor, or even a small 6" newt. That is unheard of, and would actually be easier to do, and the data would be easier to process, than fighting all the LP with a DSLR. I think that is really exciting.
Edited by Jon Rista, 24 September 2016 - 01:10 AM.