Binned / unbinned?

[badgerchap]

Hi,

I know I should probably know this by now, but what on Eart is meant by binned or unbinned, when talking about astro images? I'm sure it's something fairly simple, but I've never come across it except in people's posts, so I'm guessing it's short / slang for something?

Thanks!

[steppenwolf]

Binning is a special mode in which groups of pixels are combined to produce a single ‘super pixel’. Binning 2 x 2 means that a matrix of four pixels (2 wide, 2 deep) are combined to produce a single super pixel; this results in a pixel with four times the sensitivity but the resolution will be reduced resulting in an image one quarter the size of an un-binned image. You can also 'bin' 3 x 3 and 4 x 4.

[JamesF]

In theory, at least, binning also reduces read noise, since you only have a single read noise "event" for each group of four pixels (one "super pixel") as opposed to four. Since you get nothing for free, the cost of this reduced read noise is reduced resolution.

James

[badgerchap]

Thanks bot.

So where is this process normally insigated, and how? Is it just an option in the processing / stacking software?

[Freddie]

You set this on the capture software.

[steppenwolf]

This is instigated at image capture time.

[JamesF]

Ideally it should be done in the camera hardware.

James

[badgerchap]

Ah OK, thanks! So it's primarily a webcam thing then?

[Freddie]

Can be done on CCDs (my Atik for example) but not sure about a DSLR like your canon.

[badgerchap]

OK - I'll have a dig in the camera's software just in case, but interesting nonetheless. Thanks guys!

[JamesF]

One of the "tricks" you can use with LRGB imaging is to take the L subs at full resolution, then the RGB ones binned at 2x. You then resize the binned colour subs before combining them with the luminance for the final image.

James

[JamesF]

Ah, should perhaps point out that the reason you might do this is to reduce the amount of time required to collect the RGB subs.

James