Hi Dennis.
In the single frames that you put in the Dropbox the individual target light frame subs contain virtually nothing usable, the signal level is much too low. The calibration flats, darks and bias are all fine.
I use a conventional CCD camera and not CMOS so don't claim to be expert but from what I have read in the past and looking at the information contained in the FITS headers for your light frames you need to reduce the offset value from 50 to 25.
The gain setting you used, 139, is not adequate for the length of exposure used for this data set, 30 seconds, and all other things being equal, i.e. good observing conditions, dew free optics, well focussed, an adequate mount etc, then four or five minutes per sub would have been the approximate exposure time at 139 gain setting.
Looking at your luminance sub for example the maximum pixel value given in PixInsight's statistics module is just 0.00302, that's not even 1% of maximum pixel saturation and shows that the image is underexposed. In contrast, your Autoflat is well exposed and has a median pixel value of 0.30665, that's around 30% peak pixel saturation value.
Your flat, bias and dark are all ok, its' just the light frames that are not right.
If the mount won't support a longer exposure time then increase the gain, the read noise of the ASI1600 is very low so the camera can use higher gain settings and still produce low-noise images. Ultimately the gain setting depends on the dynamic range of the target and the Andromeda galaxy dynamic range is not that high so a higher camera gain would have been more appropriate in this case if forced to use just 30 second exposures.
Tip: When setting the camera gain value try to use even number multiples rather than odd, such as 139, as it leads to quantisation errors (rounding errors) when applied to the camera amplifiers, stick to even number values such as 60, 120, 180 or 80, 160, 240 etc. It's only a small point but it makes it easier later on when you want to accurately determine the characteristics of the camera.
Lastly, from the few stars I can see in the images it looks as though focus is a bit off and possible some tilt in the image train.
From the subs you have posted I would say there is no point you spending any more time with this particular data set, you won't be able to achieve anything to impress the wife just yet
Concentrate on the data capture side first and get that bit right rather than spending any more time post processing in PI with this data set.
If your capture software has a cursor position pixel value readout then as the image arrives after capture run the cursor over the stars and galaxy core.
For Andromeda the typical pixel value of the brightest part of the core will be something around 50% of maximum pixel saturation value. Much higher and the brighter stars will be over-exposed and blown out, much lower and the darker spiral arms will be down in the background noise. Adjust the gain and/or exposure times until you achieve that ~50% pixel saturation value and then capture a data set. you will need to increase the exposure time for the colour filters but stick to the same gain setting as for the luminance.
The cursor readout will either give a fractional value such as 0.2, 0.5 or a percentage such as 20%, 50% or a pixel count such as 20,259, 50,636 etc, just depends on the capture software you use.
Take a five minute exposure on luminance in the daytime to produce a saturated exposure and then run the cursor over the image in the capture program to determine what the 100% saturated pixel value is and then when under the stars set an exposure/gain that gives you roughly half that value in the core region of Andromeda.
FWIW Andromeda is a difficult first target and I struggled with that one too as a beginner, although it is quite big and very obvious in the sky it does not have much colour or surface brightness variability and post processing the first data set on this target can be quite uninspiring, you will find something like M42 much easier to capture and achieve a satisfactory first image, well that's my opinion anyway...
Sorry that I can't suggest anything else, hopefully the above will be of some use.
Maybe someone more experienced with CMOS cameras can help you out with more expert suggestions for image capture best practice.
William.
