Can dew on CMOS sensors be processed away?

IF it’s really affecting only isolated pixels (which is unlikely) and you are aggressively dithering every frame, the stacking filters stand a chance of mitigating the problem.  The best way to fix this is to fix the camera.  Does it have a broken seal or old desiccant?

John

Are you sure it's dew vs frost? If the latter you can try cooling down your camera more-slowly, and/or replacing the dessicant tablets.

Yuxuan:
Far too many times in the first hour or so in an imaging session I get excellent stars only to find there is a small dark patch in my subframes caused by dew on the sensor. If I zoom in, it is actually not a darker patch after all -- instead it is a few isolated pixels whose values are very different from the neighbor pixels. 

This got me wondering whether these pixels can be located and processed away using a PixInsight script. Have anyone thought about this or worked on this? Thanks!!

*It is not single pixels (I get them too and I'm not even in FL!) and you cannot process them away unless you dither every subframe by at least 10 px (larger > better). And hope ESD does its job. To be perfectly honest, I may allow 1 or 2 of them in a stack of at least 20 and prune away all the other affected frames to get a decent result.

Yuxuan:

I used to have a huge dark patch in the center of my 2600mm subs

I just turned on the ASI2600 built-in dew heater in my ASIair app, and the dark spot is gone

Unfortunately for my ASI6200 condensation occurs both on the optical window and on the sensor. Dew heater only takes care of the former.

I guess, maybe you need to replace the desiccant tablets then, as others have said

As a bandaid, you can cool less aggressively, but the only real solution is to replace the desiccant.   Processing out a dew donut isn't realistic because you just plainly won't have any signal there.

I deal with a humid atmosphere for all my imaging and have eliminated this problem by adding several additional 1/4 gram silica desiccant packets into the my ASI large format cameras. These are held in place until need for replacement by applying short pieces of Kapton (Polyimide) tape, which is non electrically conductive, can be applied to the circuit board, and leaves no residue when removed.

The four small factory supplied tablets are insufficient as they require heat/microwave treatment too often.

Additionally, I examine the sensor datasheet to note the needed temperature sufficiently cool enough that just less than one electron of thermal noise per pixel statistically accumulates over the desired subexposure time. More cooling, at least with modern sensors, in my experience, offers no discernable advantage but encourages dew or frost formation.

Running sensor cooling maximally when unnecessary also encourages avoidable faults due to eventual solder joint failures sooner than later. It is better for the hardware not to maximally thermal cycle it repeatedly if not truly required.