Flat Darks

[Groenewold]

So, I made Flat Darks or Dark Flats.. I can use those as a master-dark for flat calibration, but what about the Bad Pixel Map, should I use a longer exposed dark for that ideally?

[Haverkamp]

Yes,

flat darks will be fine for dark calibration of your flats, if they are of the same iso and exposure.

For a Bad Pixel Map, ideally you want to supply a batch of very long exposure darks on high temperature. Then you’ll defintiely get the best results. If you use exposures of less then 30seconds the BPM will be off less quality  (also depending on the sensor characteristics).

[Groenewold]

Excellent, I thought as much. But the bad pixels won’t be as prominent (I have no knowledge really on the matter so don’t shoot me) in the, let’s say, 3 min exposures versus the Bad Pixel Map I made in the oven at 20 min exposures. So is that really still the best way?

[Haverkamp]

In the oven???

[Groenewold]

Yes as hot as possible. ? (as an example of the theory ofcourse)

[Haverkamp]

The oven is a bit overdone I think…

If you make a BPM just do it inside with the sensor at room temperatures. Then you’ll need lesser darks for better statistics. This is just how the sensors work, so it has nothing to do with how I implemented this ;-)

Making it at 20 degrees Celcius or hotter will be more efficient than 0-10 degrees Celcius outside.

There is no need to put it into the oven, really ;-) Never done this myself…

[Groenewold]

Ok good to know. I was just wondering if you aren’t introducing hot pixels which only appear or are prominent at high temperatures, and if so, if this wouldn’t overly correct the 0-10 oC images.

Thanks for the heads up, I’ll make a new BPM, for now I’m using darks I made outside during the night.

[Haverkamp]

Good question.

A BPM will never over/under correct due to how it intrinsically works.

Bad Pixels behave differently than the linear pixels. The BPM correction does not do a subtract/divide on the pixel, so it can’t overcorrect the value of the pixel.

The BPM correction simply will perform a data interpolation of the Bad pixel using the surrounding good pixels ;-)

[Author]

Posts