To Bin or not to Bin

[konstantinos75]

Hi

I would like to raise this interesting topic and hear the experts opinion about this.

After some research I have done, when someone is doing astrophotography with a CCD camera attached to the telescope, it is advisable to

* bin 2x2 the exposures with R,G,B filters; this will increase the SNR of the final RGB image; it saves you a lot of time, as exposure time is reduced to half comparing to binning 1x1. For example, if with bin 1x1 you need 5 minutes exposure, with bin 2x2 you need 2.5 minutes to get the same result.

* bin 2x2 is better be done from dark skies for taking many exposures in less time.

From light polluted skies is better go with bin 1x1.

* if you need to combine the R,G,B frames with the L frame, you must not use bin 2x2 for the R,G,B frames and bin 1x1 for L frame because in this way you will loose in resolution of the final LRGB image. Instead use bin 1x1 for all L,R,G,B frames. 

* for narrowband filters you must bin 2x2 for Ha, SII, OIII to get the best result in less exposure time. But in case you need to combine these filters with L you must go with the bin 1x1 rule for all filters.

* if the image scale of your imaging device is less than 0.5 arcsec/pixel (for example you have a long focal length telescope) is better bin 2x2 all the L,R,G,B,narrowband frames.

I would like to see if these assumptions can be justified and if someone has some arguments about this.

Thank you

Konstantinos

[Pompey Monkey]

There is no "must" in astrophotography (apart, maybe, from having a good mount).

The best arguments are what you learn from experience. Personally, having spent the best part of a month's salary on a CCD and filter wheel, I'm going to use all of my pixels at 1x1 to start with and see how it goes

Experiment!

[konstantinos75]

You are right, the best thing to do is to experiment and come to conclusions.

I will come back to this when I have some new FITs at my disposal

Thank you

[Davey-T]

Have a look at this App.

Dave

http://astronomy.tools/calculators/ccd_suitability

[swag72]

I will not do anything that has a 'must ' in front of it, especially in astro imaging. To that end, I NEVER bin

[ultranova]

I am no exspert as i have only been doing LRGB imaging for a few months,

but I have tried binning the colour at 2x bin with fairly good results then putting

the colour on The L subs which are 1x bin.

Because the L is your luminance and is regarded as your sub witch holds all the

detail the colour can be manipulated more over the higher detail L sub.

I am not saying that the results would be as good as 1x bining for every thing but

having not been doing this LRGB lark very long you might need to get an answer from someone

like Olly or Sara or one of the other Astro taking giants in these forums.

[RobRob]

I bin 2x2 for auto focusing (to speed up the process) and for plate solving.

[steppenwolf]

I really only ever bin when focusing or plate-solving to speed up the process! There is a good argument for binning RGB channels but you most certainly can combine binned RGB with unbinned L - that's the way the process works! The 'detail' is held in the L channel and the colour in the R, G and B channels, you just have to up-size the R, G and B channels X 2 before compositing them with the unbinned Luminance channel.......... Or, use an RGB one shot colour CCD camera but then that would only lead to another argument

[steppenwolf]

Opps double-doubling of information there!

[konstantinos75]

Hi

Check out these experimented results by Sara Wager

http://swagastro.weebly.com/to-bin-or-not-to-bin.html

According to her conclusion: "Based on this analysis, for me the binning argument makes sense. It makes my imaging setup 2.93x more sensitive, so I will collect more faint data. For me this is important. There is a downside of course........ My sensor size of 3380 x 2704 has just halved. But by increasing the resolution of the images in Photoshop to 300DPI, I don't see that as a major problem."

So I would be particularly interested if someone else has followed the experiment path and has some data facts to present. A picture is 1000 words according to an old Chinese proverb

Thank you for your contribution to this topic

[swag72]

Hi

Check out these experimented results by Sara Wager

http://swagastro.weebly.com/to-bin-or-not-to-bin.html

According to her conclusion: "Based on this analysis, for me the binning argument makes sense. It makes my imaging setup 2.93x more sensitive, so I will collect more faint data. For me this is important. There is a downside of course........ My sensor size of 3380 x 2704 has just halved. But by increasing the resolution of the images in Photoshop to 300DPI, I don't see that as a major problem."

So I would be particularly interested if someone else has followed the experiment path and has some data facts to present. A picture is 1000 words according to an old Chinese proverb

Thank you for your contribution to this topic

I don't even follow my own advice

[graemlourens]

I ihave read tons of different approaches about this, the answer that i found is that it always depends on your setup and target.

I have tried all. Pure RGB, 1x1 LRGB, the same with narrowband, but also Lum at 1x1 and RGB at 2x2.

If youre target has a lot of color detail (fast switching color, for example Galaxies, with minute differences in colors) then binning the RGB will result in less color details.

If you're shooting a widespread nebula, binning the color there will not make a huge difference.

Another thing to consider is that if you shoot LRGB in a lightpolluted area, you're letting all the lightpollution in with the L-filter (or am i mistaken?). If you do pure RGB, the filters are mostly designed to reject the spectrum of ordinary lightpollution sources.

I have not tried binning my narrowband data, but you could only do this, if the targets Luminance is dominated for example by Ha, or this doesn't make sense (for examle NGC6960 would not work with this approach as OIII and Ha occupate vastly different regions)

Kind regards, Graem

[konstantinos75]

Hi

Thank you all for your valuable input regarding this interesting topic.

Let me add some references from bibliography about binning.

(1)

"In LRGB cases where this occurs, taking an unfiltered luminance frame using full sensor resolution and creating the individual RGB images in a binned 2×2 pixel mode will improve the SNR."

Reference:

Creating and Enhancing Digital Astro Images

Grant Privett

Patrick Moore’s Practical Astronomy Series ISSN 1617-7185

Springer Science Business Media,2007

(2)

"Obtain your luminance frames when the skies are most steady and obtain your binned RGB frames when skies are more turbulent.

"you can acquire the clear exposures binned 2 × 2 to improve your signalto-noise ratio in the dim areas."

"If you are using an H-alpha filter, consider binning your H-alpha channel 2 × 2 if needed to speed up light collection."

"Furthermore, most monochrome cameras are easy to bin 2 × 2, 3 × 3, or even 9 × 9 to allow very short exposures of deep sky objects to check centering and framing, which can be critical when trying to locate your target on a small CCD chip."

"You can gather light more efficiently if you bin your red, green, and blue channels to collect color information more rapidly while acquiring luminance information at full resolution. Because color data can be acquired with lower resolution, the color exposures in an LRGB sequence can be binned 2 × 2, accumulating in 15 min the same signal-to-noise as a 1-h color exposure unbinned."

"For very dim objects, you can obtain your clear luminance exposures binned 2 × 2 and your RGB exposures binned 3 × 3."

Reference:

The 100 Best Targets for Astrophotography

Ruben Kier

© Springer Science+Business Media, LLC 2009

Patrick Moore’s Practical Astronomy Series

(3)

"This is especially true for the commonly used strategy of binning color data with the ultimate goal of combining

it with unbinned luminance data, which may be an acceptable approach for a well sampled image but can lead to loss of valuable color information when the image is already on the verge of being critically undersampled, as is typical of

many wide field images."

"However for dim galaxies and nebulae binning the detector can yield significant time savings by lowering the read noise and making the camera act as if it is more sensitive."

"A final word about binned data. Many think that binning 2 Χ 2 automatically doubles SNR, but in reality the benefits of binning are reduced as light pollution increases."

"Even though RGB data is more forgiving than Lum data for LRGB imaging, and the reduced resolution with 2 Χ 2 binning won’t be noticeable in most LRGB images, we still shoot everything unbinned."

Reference:

The Patrick Moore Practical Astronomy Series

Lessons from the Masters Current Concepts in Astronomical Image Processing

Robert Gendler Editor

© Springer Science+Business Media New York 2013

(4)

"Luminance and color layers binned 1x1 (no binning). This provides a sharp image and good color. Highly recommended,

as it will provide the sharpest detail and excellent color. Requires additional imaging time relative to 2x2 binned color components."

"Luminance 1x1 and color layers 2x2, combined in MaxIm DL. Star images are very slightly larger when FWHM is measured, but still good."

"The main advantage of binned color components is that they take less time to acquire. If time is limited, use 1x1 binning for your luminance image and 2x2 binning for your color images."

"For higher resolution and longer exposure times, use 1x1 binning for all images."

"The ability to process the luminance image independently of the color components is a significant advantage of LRGB imaging versus RGB imaging. However, RGB images tend to have richer color, so you should choose the color combination method based on what is more important to you: color (RGB) or details (LRGB). If you want the best of both

worlds, either shoot your LRGB with the color images binned 1x1 instead of the more usual 2x2, or take longer and more RGB images to reduce noise and improve color accuracy."

Reference:

The New CCD Astronomy

Ron Wodaski

New Astronomy Press

http://www.newastro.com

© 2002 Ron Wodaski

(5)

"The argument proposes that for any given overall imaging time, a better result is obtained by using RGB at 1×1 binning than L (1×1) and RGB (2×2)."

"Binning is however, a useful technique to improve the quality of weak signals, not only for color exposures but also when used for expediency during focusing and plate solving."

Reference:

The Astrophotography Manual

A Practical and Scientific Approach to Deep Space Imaging

Chris Woodhouse

© 2016 Chris Woodhouse

So My understanding is that if someone has the possibility to go for 1x1 binning for all filters this is the choice to go.

2x2 or 3x3 binning is preferable for very dim objects.

[Adamar98]

I don't even follow my own advice

This made me chuckle.

[ollypenrice]

There are sampling rates below which I wouldn't want to go. Say 3.5 arcsecs per pixel. The loss of colour resolution and the effect on the stars becomes too great. However, when I was working with Yves at 0.66 arcsecs per pixel we would love to have binned our colour but the camera in question would not bin successfully. (SXVH36.)

Depending on the target I often make my starfields out of RGB only, no L. This gives smaller and more colourful stars. You won't be able to do this if you bin the colour.

Since I'm currently working at either 1.8 or 3.5 arcsecs per pixel I wouldn't dream of binning.

Olly