Dithering with shorter subs


#1

When taking shorter subs, being able to dither after a specified numer of subs would a big time saver as dithering chews up a lot of time. My backyard is bortle 8+ which limits my broadband sub lengths.


#2

Time saver, yes, but defeats the purpose of dithering to a large degree.


#3

Not when taking hundreds of subs.


#4

Does not matter how many you take. You still lose something by not dithering every one. More dithered frames = more quality. Fewer dithered frames = less quality. It just takes more time dithering when you have hundreds of subs. Quality always trumps speed for me but if the authors think this is a worthwhile feature, that is up to them. I would never use it, that is all I can say.


#5

There are a couple of different methods to reduce noise (which is the purpose of dithering).

  1. Dither between frames to randomize the noise distribution throughout your image stack. That means that hot and dark pixels get distributed rather than sitting on top of each other and get stacked out. If you do not dither every frame then the “noise” starts to become more prevalent and winsorized sigma clipping doesn’t work as well since the noise is now more like signal.
  2. Use a bad pixel map. This allows you to remove most all of the hot/cold pixels prior to stacking, thus dithering is not needed.

If you’re doing hundreds of subs a night it’s probably best to use method 2. Otherwise if you’re only dithering every 10 frames then you’ll just start stacking noise which is what you want to avoid.

Thanks,
Jared


#6

Thanks. Option 2 makes more sense. Dithering between 2 minute luminance subs is a ridiculous waste of time for me. Clear nights with good conditions are rare for me so I am trying to maximize the number of subs.


#7

Hi Jared,

Dithering combined with the drizzle algorithm also increases resolution in under-sampled images. Almost all DSLRs are under-sampled.

Regards,

Charlie


#8

I also dither with short 2 minute subs, it never takes long to settle afterwards, and I gladly loose some subs to the benefit of dithering, especially with a dslr, the difference is remarkable. Fix your long settle time, you will gain enormously in quality …


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