Automatic dark frame selection by sensor temperature and exposure - with linear interpolation

[Borodog]

Well, it's time I requested this.

I would like a feature that automatically applies matching dark frames based on the sensor temperature and exposure time. Gain and offset/brightness also need to match.

Furthermore, the actual darks applied should be synthetically constructed for each light by linear interpolation, in both temperature and exposure, from the nearest bracketing master darks in the library.

Over the past couple of days, I used a variety of environments (living room, hot garage, in the fridge, in the freezer) to produce a set of master darks for my uncooled ASI183MC at various temperatures. Because I didn't have perfect temperature control, I ended up with good masters for some odd intervals, 13C, 14C, 18C, 23C, 24C, 29C, 37C. With a little more work I could fill in some of the large gaps, but luckily, I don't have to. I've confirmed that, for example, a linear interpolation of the 14 and 18C masters will correct any temperature between them adequately, including amp glow.

Similarly, two master darks at the same temperature (and gain and offset) but different exposure times can be linearly interpolated to better match any exposure between them. In contrast to dark scaling, which requires a bias and cannot be done for a camera with amp glow, dark interpolation does not require the bias to be removed and works perfectly in a camera with amp glow.

In fact, it should be possible to better match an interpolated synthetic dark to temperatures as they change for an uncooled camera, as well as to better match unusual exposure times that, for example, have been recommended by the SharpCap Smart Histogram, both at the same time. As long as you have a library of a few master darks that span the expected ranges of temperature and exposure, you should be good to go. It would be amazing if SharpCap could handle this on the fly without user intervention.

There would need to be special treatment for hot pixels that are fully saturated in one dark but not the other. The correct procedure is to fully saturate them in the interpolated dark and treat them via the usual method for fully saturated hot pixels when dark subtracting the light, i.e. grabbing a neighboring value.

This technique would be applied automatically to every light as it comes in. Hence, the synthetic dark would always match every light as closely as possible without user intervention to swap out darks.

Thank you for your time and consideration.

Edit to add: Obviously for the temperature interpolation to work, your camera must report the sensor temperature, even if it is not cooled. My ASI183MC does this, for example.

[Borodog]

As an illustration, here's a heavily stretched small stack of 75s darks, taken within 0.5C of 16C, calibrated with a synthetic master dark created by linear interpolation between 2 master darks at 14C and 18C. The amp glow is perfectly calibrated and the (signed) average ADU in the calibrated stack is very close to zero.

[Steve in Boulder]

Excellent idea.

[ESCelestron]

+1

[RMSQueenMary]

That is a cool idea.

[mjritchie]

+1

[Tiago Ferreira]

+1

[kite55surfer]

+1

[brushpilot]

+1