CanonEOSII RebelT7i 'mod. UV-IR @ Hutech' thru a TPO80A filter thru a TeleVue 2.5XPowerMate for 3000mmF/l on an Astro-Physics 1200GTO '2010' Mount for four CR2.s at 668secISO6400 and 'calibrated' in MaximDL Pro V6.16 and Average stacked . Then the 16BIT FITS was put into "ImagesPlus" for more commands .x {This image is four CR2.s Average stacked which I read in an old CCDOps webpage that to 'average' four images together 'doubles' the SNR … is this better than Sum stacking which might just make the stacked image thicker with the same SNR as a single image ?}
No, there is absolutely no difference whatsoever between these two things, except for a scaling factor. Average = (A + B + C + D) / 4. Sum = A + B + C + D. Therefore Sum = Average * 4. Obviously taking an image and simply multiplying every pixel by a constant does not change the signal-to-noise ratio. It increases the signal by 4 and increases the noise by 4. Average has exactly the same effect on SNR as Sum.
