Add option to save live stacking raw frames with and without calibration masters applied

[Borodog]

Currently I believe the raw frames are saved without calibration frames applied. I would like an option to save them with the current master dark and flat applied as well.

[admin]

Hi,

can I ask you why you want to do that? Often understanding the reasons for this sort of thing helps me out with either understanding what the feature should do or suggesting alternatives.

For instance in this case I would wonder about other processing functions - line suppression, background removal, satellite trail removal... Would they be applied too or just dark and flat?

There is always the option of running the saved raw frames (without dark/flat) through the folder monitor camera using the dark/flat and re-saving.

cheers,

Robin

[Borodog]

Fair enough. This is a bit involved, so bear with me.

As you may recall, I have an uncooled astro camera (ASI183MC). The sensor temperature changes over time with gain, exposure, ambient temperature, and the thermal inertia of the camera and sensor itself. I have been thinking of ways to get the best possible images I can out of it, and dark frames are a particular weak spot. As the temperature changes, particularly as it drops over the course of the evening, darks begin to over-correct. I can try to take darks at the start of imaging and at the end of the night to bracket the sensor temperature, and that works ok enough for a small range of temperature. But for a larger range of temperature, it is definitely not optimal; I can see the difference in dark correction with as little as 1-2°C of sensor temperature change. Furthermore, because I don't have a dark library, it eats up a lot of imaging time to shoot darks every time.

So I was thinking, how can I build a dark library? I picked a cloudy night and just stuck my camera and laptop outside to shoot darks (a normal capture, not "Capture Dark" or live stack) at 30s, gain 111, offset 4, which is about my standard recommended by the Smart Histogram. I just left it capturing images as the temperature dropped. They are all tagged in the filename with the sensor temperature. So I am now able to stack them in 1°C bins. Some bins will have more frames than others, but all of them have plenty enough. So then I would be able to live stack and just drop in a new dark as the temperature dropped (would be great if SharpCap could do that automatically but that's probably asking a bit much). Which is great for live stacking, but is problematic for stacking in post in something like SiriL, which I definitely want to do in order to cull bad frames. I mean, I could do it, but it would be laborious. Whereas if the raw frames could be saved with calibration, it becomes trivial. Just stack the pre-calibrated lights.

I believe I could do what I want if I skipped live stacking and just captured a normal sequence, which saves with the calibration frames applied. But then I miss the fun of live stacking while capturing, which is at least half the fun. I want the best of both worlds.

As far as other features like banding, background, satellite trails, I don't really have much opinion, as I don't tend to use any of those while capturing. It does seem that since they are enabled for live stacking it would be simplest to leave them on for writing the raw frames. You might even be able to write out the registered (i.e. aligned) frames instead of the unaligned frames. I'm not sure what would be easiest for you, which is probably what you should do. I'll never get the feature added if I make it to onerous to implement. ;O)

[Borodog]

Also, can you elaborate on this?

"There is always the option of running the saved raw frames (without dark/flat) through the folder monitor camera using the dark/flat and re-saving."

How does that work? If you dump a bunch of files in the monitor folder, does SharpCap process them all in order or something? Does that work for any capture method? Regular sequence? Live stack? Capture Dark or Flat?

[admin]

Hi,

thanks for the great explanation - there is some interesting stuff there for me to think about. The idea of having save individual frames as 'unprocessed', 'processed' or 'both' is a possibility I guess (but the UI needs to be simple enough not to confuse people). Also the idea of making more of the dark library concept and auto-selecting the dark as the temperature changes is not too far fetched.

If you point the folder monitor camera at a set of frames then it will process each in turn, basing the ordering off the file time stamps. This can either be run as a 'play' operation where each frame will process straight after the previous, or by single stepping. The single step approach would let you change darks, but it's a lot of work as you say.

cheers,

Robin

[Borodog]

Well if you’re looking for ideas related to darks, I am full of them.

In addition to auto-selecting matching darks (by exposure, gain, offset, temperature even) you could do even better by interpolating between darks of the same gain and offset, linearly interpolating between the two nearest temperature darks. Or parabolically between 3. If you have a matching master bias you can even scale the exposure, as both amp glow and dark current scale linearly with exposure (for most cameras; may not work with a 1600 or 294).

[admin]

Hi,

there are some issues with interpolation - for instance 'amp glow' that you see in some cameras does not respond to temperature in the same way that the more general thermal background does. Additionally, warm/hot pixels would probably need special treatment. I guess the benchmark is the test to see if an interpolation between a 10C and 15C dark works better against a 12.5C exposure than either the 10C or 15C dark...

cheers,

Robin

[Borodog]

I’ve tested interpolation and it works great, correcting both dark current and amp glow. I never did anything special about hot pixels and never saw any problems. It just works.

[admin]

Thanks, good info to have

cheers,

Robin

[Borodog]

Dr. Glover,

Is there any update on being able to save live stack raw frames with calibration applied?

Thanks for your consideration.