Problem with DARK and BIAS ADU

[-Amenophis-]

Hello everybody,


I am writing to you about a problem to calibrate my darks.

After doing a masterbias using 100 bias, I made the superbias via the process icon in pixinsight.

When it comes to calibrating DARKS with superbias, I have problems.
Indeed, the bottom of the image is degraded enormously.

The cause ?
the ADU value of my DARKS are lower than the ADU value of the superbias. So, when subtracting superbias, I find myself with a lot of black point ....





After calibration with superbias :





I know there is a way to solve the problem.
Including decreasing the ADU of the superbias.
By cons, I do not know how to reduce this value.

Could you help me on this?

Thanks a lot for your help.

[bulrichl]

Hello Amenophis,

when inspecting the pre-calibrated MasterDark with the Image/Statistics process please uncheck 'Unclipped'. You will then see the fraction of pixels that are NOT clipped in the pre-calibration of the MasterDark (count [%]). Alternatively view the histogram of the pre-calibrated MasterDark with the IntensityTransformations/HistogramTransformation process (you will have to use a horizonal zoom of about 100 or 200): it will be clipped severely. I don't know why some tutorials recommend pre-calibrating the dark frames.

The solution will be, not to pre-calibrate the dark frames or the MasterDark, but to let the calibration of the MasterDark be executed during the light frame calibration process.

Take a look here: https://pixinsight.com/forum/index.php?topic=11968.0

Bernd

[-Amenophis-]

Thank you very much for your message.
I will read (and do the translation) to understand