Dithering and Binning

[Corries]

I have been watching the Harry Page video tutorials which have been an enormous help in understanding PixInsight but I have a couple of questions.

In the Alignment and Integration video he advises that your images are Dithered and in the LRGB Combination video he talks about an image that is Binned.  I know what dithered and binned mean because I looked it up in a glossary but can anyone tell me how you get images that are binned and dithered? 

Many thanks.

[Geoff]

These are both set via camera control and guiding software.  It's something that has to be done pre-PixInsight.  The attached file shows how to do it in Maxim.  Presumably other software will have something similar.

[pfile]

right - binning will be set in camera control and dithering is the responsibility of your auto guider. the camera control program asks the auto guider to move the guidestar a little between exposures.

rob

[Corries]

I'm a little confused about binning.  If using binning reduces the resolution of your images, why would anyone use it all?

Can anyone explain?

Thanks.

[Josh Lake]

Two reasons. First, by putting the photons from four pixels into one pixel, you essentially increase your signal to noise ratio. Second, it was thought that since all of your detail comes from the Luminance layer, it's okay if the RGB chrominance layer is lower-res, even a bit blurry. That assumes you are taking separate luminance at full 1x1 binning and combining later. If you shoot just RGB and extract L, you'd want full res.

I suppose a third reason might be file size and memory concerns, but that's hardly an issue these days with huge, cheap HDDs.

That's the common explanation, but I shoot everything full res.

[chris.bailey]

Binning may not reduce the real resolution. Small pixels on a long focal length scope will tend to be oversampled i.e. have a pixel resolution that can't be gained from the scopes limit of resolution or the sky conditions. Binning then gives a better signal to noise ratio and gives a better match. Counterintuitively stars tend to be sharper in appropriately sampled images to those that are significantly oversampled.