Black level

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Re: Black level

by han.k » 01 Oct 2018, 14:58

Okay, I made the change permanent in ASTAP 0.9.120 just uploaded. No other changes.

Re: Black level

by Serg1 » 01 Oct 2018, 04:40

Hello Han.
AstapX version works.
There is another problem, open in a new topic.

Re: Black level

by han.k » 30 Sep 2018, 22:13

Hello Serg,

CCDstack and PI calls this extra value a "pedestal". I will make the change of astapX permanent and call this value pedastel. I will add it to the reporting and FITS header. Will finilize it tomorrow as ASTAP 0.9.120.

Can you check if the astapX version works well for you?

There are more people having a similar problem:
https://www.cloudynights.com/topic/5428 ... sic-terms/

Regards, Han

Re: Black level

by Serg1 » 30 Sep 2018, 20:38

In Fitswork, you can change the black level on the histogram.
Setting in the ASCOM driver not change.
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Re: Black level

by han.k » 30 Sep 2018, 20:16

Serg1 wrote:
30 Sep 2018, 19:57
This file is blue filter. The sky dark. The milky way is clearly visible.
Okay. I looked to some other stack programs. Could not find any setting to set an offset for this problem. So how did they solved this?

Have you any experience with an other stacking program or an idea how they solved it? I could add a fixed value of 100, but with the value zero you could measure the background. So maybe the current solutionin astapX is fine. Only I like to have the minimal amount of settings.

As in previous post, did you change any setting in the ASCOM driver between making darks and lights?

Han

Re: Black level

by han.k » 30 Sep 2018, 20:11

Hello Serk,You files look normal to me. Gain is stable, temperature is equal. The only thing noticeable is that the light exposure didn't result in in a higher background.

Looking to my own H-alpha images, the signal level is after 200 seconds about 100 above the background. So result is positive.

So you have either super dark skies or the camera is drifting which is unlikely. Did you adjust any offset setting in the camera ASCOM driver?

Han

Re: Black level

by Serg1 » 30 Sep 2018, 19:57

This file is blue filter. The sky dark. The milky way is clearly visible.

Re: Black level

by han.k » 30 Sep 2018, 19:40

Hello Serg,

I have created a special version of ASTAP, called astapX.exe. In this version you can set an offset in the menu tab STACK METHOD. Near stacking method. This version I added to the following file:

http://www.hnsky.org/astap.zip

Try this version.

I will check your files.

For my files, the dark average pixel is around 300. Taking a 50 seconds exposure increases the background to 1500 at sky with a SQM value of about 20.4. I don't understand why your images are different but let's investigate. Only thing I can could think of is that you have super dark skies which is good.

Regards, Han

Re: Black level

by Serg1 » 30 Sep 2018, 19:16

Han, I e-mailed the files.
Camera Skyrus453M-ICX453AQ.

Re: Black level

by han.k » 30 Sep 2018, 18:19

I was too quick. Yes your correct, the sum of the light offset and dark offset should be zero. You will need them only to keep the noise in the dark current and other noise positive.

I will look into the code what I did. For most cases the light polution will generate enough signal to stay in the positive range. Adding an adjustable extra offset is easy.

Can you send me a light frame and dark frame for testing?
What camera are you using?

>>Can I save this offset in the light sum file?
The -32 FITS format (float) should be able to store any value, also negative. If the singal is positive also the FITs 16 bit will do, else it will be clampped to zero if negative

Regards, Han

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