Author Topic: Dark/Bias subtraction question  (Read 2544 times)

Offline adl

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Dark/Bias subtraction question
« on: 2010 November 07 10:23:38 »
I have prepared integrated Dark and Bias frames (no Flats...) using the Image Integration Tool, and have a question about the Image Calibration Tool.  When I subtract the Darks and Lights from my Light Target Frames (following the PI tutorial), does the IC program automatically subtract the integrated Bias Frame from the Dark Master before it then separately subtracts the Bias Master from the Light Frames?  In other words, the Master Dark Frame I prepared using the Image Integration Tool contains the Bias information (since the Bias wasn't subtracted THERE), so I want to just confirm that the Bias isn't subtracted TWICE from my Light Frames using the IC Tool (meaning, once as a (scaled) subtraction resulting from the Dark Frame subtraction, and then again as part of the "regular" Bias Frame subtraction).

Thanks for any clarification here!

Offline Juan Conejero

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Re: Dark/Bias subtraction question
« Reply #1 on: 2010 November 07 13:49:53 »
Hi,

If you are following Vicent's s tutorial (which is highly recommended) then your master dark frame has been just integrated and not bias-subtracted. In this case you must make sure the Calibrate check box is checked for the Master Dark section of the ImageCalibration tool.

Following the same tutorial, individual flat frames have been bias-subtracted and dark-subtracted (with dark optimization) before integrating them into the master flat frame. Hence, you must uncheck the Calibrate option for the Master Flat section of ImageCalibration.
Juan Conejero
PixInsight Development Team
http://pixinsight.com/

Offline adl

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Re: Dark/Bias subtraction question
« Reply #2 on: 2010 November 07 14:57:31 »
Thanks very much, Juan.

Just to confirm (and I AM using Vincent's tutorial, with the Master Bias and Master Dark Calibrate boxes CHECKED, and the Master Dark Optimize box CHECKED, in the IC Tool): if I do NOT use any Flats (for now...), can you confirm that I am *not* double-subtracting the Bias frames by following this procedure?  The output looks great, but I want to be sure I'm proceeding properly.

Thank you again.

P.S. Only a new user, but PixInsight is a strikingly impressive program!

Offline Juan Conejero

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Re: Dark/Bias subtraction question
« Reply #3 on: 2010 November 07 15:09:02 »
Quote
can you confirm that I am *not* double-subtracting the Bias frames by following this procedure?

Absolutely. The master bias will be subtracted from your target light frames only once. Each Calibrate check box affects exclusively to its corresponding master frame; it has nothing to do with the target frames.

Quote
P.S. Only a new user, but PixInsight is a strikingly impressive program!

Thanks! :)
Juan Conejero
PixInsight Development Team
http://pixinsight.com/