MaxIM calibration process - behind the scene

[shahgazer]

Hi All,

Posted this question on maxim yahoogroup but no response there, hope fellow IIS can help me out..

I am curious about the calibration process done by Maxim.

Let say I have a set of LRGB, uncalibrated images, that I want to combine stack. I already have a set of Master darks, flats and bias generated (for each LRGB sets) under "Set Calibration" option.

After selecting the LRGB files in the "Stack" window, I checked "Auto Calibrate" option, and the Combine it.

So, I wonder, does each of the LRGB sets are being calibrated first , before combining into the final Color image? For example, if I have a set of 5 Red image, are they being calibrated individually or only after combining the 5 sets into 1 stacked Red image?

I've read some tips on processing LRGB images, saying that it is best to calibrate individual LRGB first, before stacking. I'm pretty new in CCD imaging and would like to understand more on the concept and what's going on under the hood of Maxim.

Reading at http://starizona.com/acb/ccd/software/soft_total_ngc253pm.aspx , it seems I have to do almost manually for each filter set, or not?

Anyway, this is among my first attempt on CCD imaging, on Eta Carinae, from my site (Kuala Lumpur), it never rises above 30 degree, this one is Luminance only, telescope Skywatcher Equinox 120ED and QHY9.

http://www.falak-online.net/gallery2/main.php?g2_view=core.DownloadItem&g2_itemId=6475&g2_serialNumber=1

I got a RGB sets, but never really get the same clean results as with the Luminance data. Probably I did not dither during each exposure to reduce the noise further.

Thanks for any tips.

Regards
-Shah-

[Bassnut]

Yes, Maxim calibrates each image first before combining. It searches your calibration database for the appropriate frame to calibrate with. You should have this database loaded with all the master calibration frames (prestacked) required for each filter (darks and flats, depending on how you set cal up) and the FITs headers must be consistant for the process to work properly. Making master calibration frames is a seperate proceedure you must do 1st.

Although I use DL for creating calibration frames, I use CCDstack for processing images. Its more manual but gives more control and superior results.

Overall though, DL is fine and gives fast (automatic) results for all but the most difficult raw data.

[shahgazer]

Thanks Fred for the insight.

However, if I were to follow the workflow on http://starizona.com/acb/ccd/software/soft_total_ngc253pm.aspx , I guess I still have to process individual groups first (with Maxim auto calibrates each image..no need to worry on that one) , and then color combine them?

Looking through the options in Maxim, I guess if I want to do that automatically, I need to create a script ?

I already have the master calibration files done before so, I just 'check' the Auto-Calibrate option when Stacking.

Regards

[Bassnut]

Yes, stack individual groups. Although you could script for total automation, you wouldnt usually want that because groups may require different treatment, eg bloom removal. Its good to have some manual control.

From memory you only need to check auto calibrate, to calibrate auto matically. Not sure if that is done as part of the stacking command.

This is all covered in the help file.