Black on images

[Fay]

I noticed black spots n my images so did a new set of darks. it is the same. i have tried different stacking methods in DSS & AA, to no avail.

Does anyone know what can be causing them? driving me nuts!!

Thanks


Fay

[MarkS]

It might help if you post an example image.  Otherwise, you need to start from first principles and work out when the black spots first appear:

Are they in the raw subs?
If not, do they appear when applying dark, or flat or bias?
If not, do they first appear when registering the images or when stacking?
If not, is it something you are doing in post processing?

Mark

[Les R]

Dust on the sensor?

Are the dots in the same places each photo?

[Fay]

in AA i have opened 1 light & 1 dark. and I can see that the hot pixels seem to be in the same place.

i stacked the dark onto the light and the pattern of the original hot pixels has gone. what is left are lots of black specks but in different positions

[MarkS]

Which camera are you using? 
Does it have set point cooling? 
Is it possible that the darks were taken at a higher temperature than the lights - this would cause "over-subtraction" and hence black pixels.

[Fay]

Hi Mark,

QSI -120 c darks taken at same temp.

hope you can see the above ok. 1. dark & light stacked, 1. light 3. dark

[Fay]

or, some of the hot pixels are taken out but not all.

[mickw]

Dead pixels ?

They should show as black spots on the flats ?

Isn't there a procedure in AA for bad pixel mapping ?

[Fay]

Perhaps Defect Map correction on the stacking page. but dont know how you get a map, or make it

[Fay]

I have just done a DSS stack using cosmetic pixel removal, and i cant see any specks. this could be a fluke!!!!

[mickw]

this could be a fluke!!!!

I agree, I didn't expect to be right 

[Mike]

Isn't a dead pixel and a hot pixel the same thing as far as the stacking procedure is concerned?

[The Thing]

Isn't a dead pixel and a hot pixel the same thing as far as the stacking procedure is concerned?

DSS has Hot and Cold pixel removal on the Cosmetic tab as well as hot pixel detection on the Darks tab. I am not too sure what the parameters do as my understanding is Dead pixels have no value e.g. R0 G0 B0 and are therefore black, with no noise floor value and Hot ones R255 G0 B0 for instance (could be green or blue as well) are stuck full on whatever colour they represent in the Bayer matrix, they always read out full of electrons. If a mono chip they will of course be white/max luminance. The DSS sliders indicate it's not quite so clear cut...

[Mike]

But if you dither between frames, if it is a hot or a dead pixel, it will average out.

[The Thing]

But Fay likes to dither (and dally) before she even starts imaging. This averages out as an early night for her and better conditions for the rest of us!