FOLLOWUP EDIT - One of the original conclusions below was that binning did not result in a significant reduction in the image noise. Since posting this work, I have discovered that this is because of the noise reduction work I had performed on the original image. The SNR improvement from binning would have been more significant if I had not already done any noise reduction on the image.

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Binning is an important topic for all of us, but particularly those of us fortunate enough to have full frame sensor (9576x6388 pixel) cameras like the ASI6200. Rodd motivated me to do a bit of investigation, which I am sharing here for those of you who may be interested. I have attached some binning examples, but first a bit of background.

Binning can be done either directly from the camera, or afterwards during software processing. With almost all of today's CMOS cameras, there is no difference to binning from the camera or with software (it is advantage to hardware bin with CCD cameras).

Here is a quick pro/con summary of binning for CMOS cameras:

Advantages:

- Slight improvement of SNR

- Faster and more reliable image transfer from camera (if done that way)

- Faster image processing

- Faster viewing and download of Astrobin images

Disadvantages:

- Reduction in resolution

Here are some useful links with more detail on binning:

- Everything you need to know about Binning

- CMOS vs CCD Binning

- Binning

- Understanding Binning

For this study, I compared 3 levels of binning for a recent images of mine (NGC 7331), using Pixinsight's Integer Resample / Average process :

- Original image (6080x4395)

- 2x Binning (3040x2197)

- 3x Binning (2026x1465)

For the 3 different ways to see an object in Astrobin, here are my observations:

1. Thumbnail (Initial Screen)

In my opinion, there is no difference between the 3 Thumbnail images.

2. Windowed (1st click)

In my opinion, there is little difference between the 3 Windowed images. The SNR improvement from binning is detectible but only on close examination.

3. Full Resolution (2nd click)

This is the only view where the different pixel dimensions (image size) are apparent. The SNR difference is more noticeable but not significant.

So what does this all mean? Here is my view:

- If the object takes up most of the image, binning seems like a good idea. This is probably the case for most of our images, as long as the width remains above about 2000 pixels. For this object, binning at 3x means that Full Resolution doesn't present a larger image than the Windowed view, but I don't see a big downside to that.

- If there are details in the image that need to be preserved at full resolution, it may be best not to bin. For example, a galaxy cluster is fun to examine for the individual details of each tiny galaxy. Likewise, a poster of Messier objects may be best preserved at its original detail without binning, so that each object can be seen clearly in the full resolution view.

- If the object is something that is to be printed, it may be best not to bin in order to maintain the full resolution, especially if the image is printed at a larger size.

Comments and corrections are appreciated.