Too bin or not to bin...that is the question
Posted: Tue May 03, 2022 10:54 am
Having a little photography background, I have always tried to image with the highest resolution possible. Using Photoshop it is much easier to 'soften' images than sharpen them.
When I started astrophotography I kept the same philosophy i.e. always image at the highest resolution. I have read many articles related to the pro's and con's of 'binning'. To me 'binning' is just throwing away resolution. There is a difference with astrophotography, and that is there is a point where higher resolution does not provide more detailed image. This is related to sky quality and 'seeing'. Based on atmospheric conditions the best resolution that you can attain is between 1 arc-sec to 2 arc-sec even with good clear skies. So imaging at higher resolution than that does not increase the details in the image.
One of my imaging setups utilizes an 11 inch SCT and a ZWO ASI2600 camera. Based on the focal length of the scope and the size of each pixel, that setup has a 'resolution' of about 0.396 arc-sec/pixel. Astronomy call this 'over-sampling', since the best seeing limits 'resolution' to 1-2 arc-seconds. To compensate for this, you can select a different 'binning' mode for the camera. Binning is essentially adding the output of adjacent pixels to make one larger pixel. Binning 1x1 takes every pixel as a single entity. Binning 2x2 takes four pixels and adds them to make one pixel four times larger. Binning 3x3 takes nine pixels and adds them together, etc. Binning reduces read noise and also allows for shorter exposures.
But does binning sacrifice image quality??
All of the experts say you should do binning if your setup is over-sampling. So I decided to run my own test. I took one hours worth of images (thirty 2 minute exposures) with the camera set for 1x1, then 2x2, then 3x3, then 4x4. All in the same night under same conditions. I also collected darks, flats, and biases for each configuration.
I then processed them the same using Pixinsight. In order to keep everything fair, I only processed the images up to the point of stacking them. This included flat calibration, flat master, image calibration, star alignment, local normalization, stacking, background extraction, denoise, autocolor, and ArcSinH stretch. I stopped at this point because going any further is simply 'photoshopping' and I wanted to evaluate and compare the 'raw' stacked version.
So attached is the result of imaging at 1x1, 2x2, 3x3, and 4x4 binning. It should be noted that files sizes are dramatically different. The 'raw' FITS 1x1 file is 50,969KB, the 2x2 file is 12,747 KB, the 3x3 file is 5,668 KB, and the 4x4 is 3,183 KB.
Tell me if you can see any difference.
This pretty much convinces me that the experts are correct. Binning up to the point of being within the 1-2 arc-sec/pixel does not reduce image quality. Do you agree????
I will next complete the image processing of each version and see if there is any difference. I may then even have each printed 8x10 to see if there is any difference when printed. I know this sounds like an over-reach, but I think it is worth the effort.
Roger
When I started astrophotography I kept the same philosophy i.e. always image at the highest resolution. I have read many articles related to the pro's and con's of 'binning'. To me 'binning' is just throwing away resolution. There is a difference with astrophotography, and that is there is a point where higher resolution does not provide more detailed image. This is related to sky quality and 'seeing'. Based on atmospheric conditions the best resolution that you can attain is between 1 arc-sec to 2 arc-sec even with good clear skies. So imaging at higher resolution than that does not increase the details in the image.
One of my imaging setups utilizes an 11 inch SCT and a ZWO ASI2600 camera. Based on the focal length of the scope and the size of each pixel, that setup has a 'resolution' of about 0.396 arc-sec/pixel. Astronomy call this 'over-sampling', since the best seeing limits 'resolution' to 1-2 arc-seconds. To compensate for this, you can select a different 'binning' mode for the camera. Binning is essentially adding the output of adjacent pixels to make one larger pixel. Binning 1x1 takes every pixel as a single entity. Binning 2x2 takes four pixels and adds them to make one pixel four times larger. Binning 3x3 takes nine pixels and adds them together, etc. Binning reduces read noise and also allows for shorter exposures.
But does binning sacrifice image quality??
All of the experts say you should do binning if your setup is over-sampling. So I decided to run my own test. I took one hours worth of images (thirty 2 minute exposures) with the camera set for 1x1, then 2x2, then 3x3, then 4x4. All in the same night under same conditions. I also collected darks, flats, and biases for each configuration.
I then processed them the same using Pixinsight. In order to keep everything fair, I only processed the images up to the point of stacking them. This included flat calibration, flat master, image calibration, star alignment, local normalization, stacking, background extraction, denoise, autocolor, and ArcSinH stretch. I stopped at this point because going any further is simply 'photoshopping' and I wanted to evaluate and compare the 'raw' stacked version.
So attached is the result of imaging at 1x1, 2x2, 3x3, and 4x4 binning. It should be noted that files sizes are dramatically different. The 'raw' FITS 1x1 file is 50,969KB, the 2x2 file is 12,747 KB, the 3x3 file is 5,668 KB, and the 4x4 is 3,183 KB.
Tell me if you can see any difference.
This pretty much convinces me that the experts are correct. Binning up to the point of being within the 1-2 arc-sec/pixel does not reduce image quality. Do you agree????
I will next complete the image processing of each version and see if there is any difference. I may then even have each printed 8x10 to see if there is any difference when printed. I know this sounds like an over-reach, but I think it is worth the effort.
Roger