Binning a flat frame - Is this possible

[Catanonia]

Maybe a silly question, but is the following possible / wise

• Taking a 1xbin flat frame integration and x2 software binning to create a 2xbin flat frame  (Assuming the focus and image train is the same)

Obviously best to do dedicated 2x bin flats, but lets assume you forgot to take them but have 1xbin flats from the same session

Logic tells me it should work, but I am always wrong

Thanks

 

 

Edited March 17, 2022 by Catanonia

[ollypenrice]

I'd certainly try it. Professional astronomy flats contain pixel by pixel information which would, of course, be lost in binned flats. I doubt that amateur flats do so, though. We're just trying to correct for the broad inequalities of the light path.  You'd want to use unbinned darks-for-flats to calibrate the unbinned flats, though, before software-binning them to match the lights. There might be other effects coming into play as well. Given that flats taken strictly by the book sometimes play up (usually by over-correcting) I think that predicting the outcome of your proposal might be difficult.

Just try it, say I.

Olly

[vlaiv]

Simplest approach is to calibrate your subs and then bin them - or even bin after stacking while data is still linear.

Last option is quickest and first reduces storage space requirements for stacking.

In theory, you can bin all of your subs prior calibration - that means lights, flats, darks, flat darks - what ever you use, and that is equivalent to "firmware" binning - or letting your CMOS camera firmware bin data for you (not the same as CCD binning on camera - but the same as software binning you would do), but I'm against that sort of thing because you loose some of control.

For example - you loose ability to bin in more sophisticated ways than regular sum / average bin. For example - you could have hot pixel map and remove hot pixels from binning process - so most 2x2 (or 3x3 - it does not matter) groups of pixels would average all pixels, but some will simply exclude hot (or dead) pixels and average 3 out of 4.

As far as mathematics goes - order of operations makes no difference if you use regular calibration and binning - so you can calibrate binned data or bin calibrated data.

 

[Catanonia]

Excellent, thanks gents. It was something I thought would not be a problem reducing the image size from big to small (binning) and going this direction "should" work.

Will experiment in taking my master 1xbin flat and Integer Reducing it to a 2xbin and see what happens to the subs after calibration.

If that doesn't work, will take the actual individual flats, bin them and then integrate them with their appropriate 2xbin bias and darks.

 

Edited March 17, 2022 by Catanonia