Author Topic: New tutorial: Master Calibration Frames: Acquisition and Processing  (Read 35704 times)

Offline georg.viehoever

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Juan,

as you know, Canon EOS cameras are sometimes plagued by the banding noise, as shown in http://pixinsight.com/forum/index.php?topic=1159.msg5638#msg5638 . This also affects the dark, flat and bias frames (primarily the darks). I think it is best described as some kind of read noise that is loosly correlated between different shots (but not exactly).

Since PI calibration mainly depends on analyzing the thermal noise: Is it necessary to remove the Canon read noise, e.g. by using the CanonBandingReduction script before calibrating?

Georg
Georg (6 inch Newton, unmodified Canon EOS40D+80D, unguided EQ5 mount)

Offline vicent_peris

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Juan,

as you know, Canon EOS cameras are sometimes plagued by the banding noise, as shown in http://pixinsight.com/forum/index.php?topic=1159.msg5638#msg5638 . This also affects the dark, flat and bias frames (primarily the darks). I think it is best described as some kind of read noise that is loosly correlated between different shots (but not exactly).

Since PI calibration mainly depends on analyzing the thermal noise: Is it necessary to remove the Canon read noise, e.g. by using the CanonBandingReduction script before calibrating?

Georg



I think it would be helpful to remove banding to each calibration frame. Once you have masters without banding, you can subtract thermal noise to light frames.


V.

Offline Niall Saunders

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Folks,

I hope nobody minds, but I have started a new topic, based on Juan's detailed reply, to allow the 'intricacies' of the new ImageCalibration process to be discussed away from the 'generalities' (or the 'how do I use the new IC process' type of questiopns).

Cheers,
Cheers,
Niall Saunders
Clinterty Observatories
Aberdeen, UK

Altair Astro GSO 10" f/8 Ritchey Chrétien CF OTA on EQ8 mount with homebrew 3D Balance and Pier
Moonfish ED80 APO & Celestron Omni XLT 120
QHY10 CCD & QHY5L-II Colour
9mm TS-OAG and Meade DSI-IIC

Offline mattssporre

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Juan,

thanks for the explanation. I might need to contemplate over some of the statistical issues here but one statement in your made it click into place (at least in my head  ;))


As S and Ns remain unchanged during the whole process, what we are minimizing is actually the standard deviation of:

D - k*D/ki + Ns


I understand that your procedure do just this and that it would approach an approximation of D (given that the problem is stable etc). Your are not realy finding the optimized dark by minimising Sqrt(Nd*Nd + Ns*Ns) as I missunderstood you. It was the word "noise" that confused me since I do not see the Dark Signal as noise, just as unwanted signal.

BR
Matts

Offline NKV

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Juan, what about "Pedestal" during calibration? See pic.

My camera has a thermostabilisation CCD, but it has a temperature dependence of Bias. Average Bias increases with temperature. For example freeze CCD on-40oC ambient temperature of 20 ° C average 1924ADU, ambient 5 ° C-average 2000ADU. The mean deviation stable 5.5ADU
Therefore, if the ambient temperature drops during the session, the calibration process may fall below zero. To avoid zero clipping I deducted from the master of Bias 100-200AUD, with dark calibrated separately.
But I think it will be good if will be able to specify the value of the pedestal in future versions.

Offline Mike Reid

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Thanks Vicent for the tutorial!

I have a typical LRGB set of calibration frames where I'm shooting L at 1x1 binning and RGB at 2x2 binning.  I tried to follow Vicent's tutorial and these are the steps that I did to generate my 8 master calibration frames,


  01. integrate 1x1 bias frames                 => MasterBias_1x1.fit
  02. integrate 2x2 bias frames                 => MasterBias_2x2.fit
  03. bias calibrate 1x1 dark frames
  04. bias calibrate 2x2 dark frames
  05. integrate 1x1 calibrated dark frames      => MasterDark_1x1.fit
  06. integrate 2x2 calibrated dark frames      => MasterDark_2x2.fit
  07. bias and dark calibrate L flats frames
  08. bias and dark calibrate R flats frames
  09. bias and dark calibrate G flats frames
  10. bias and dark calibrate B flats frames
  11. integrate calibrated L flats frames       => MasterFlat_L.fit
  12. integrate calibrated R flats frames       => MasterFlat_R.fit
  13. integrate calibrated G flats frames       => MasterFlat_G.fit
  14. integrate calibrated B flats frames       => MasterFlat_B.fit


Does this seem correct?

Each of these steps required filling out a form and running the module.  It took quite a lot of time and there were several opportunities to select the wrong files. Since my settings for these steps (more if I acquire Ha also) rarely change this would seem to be an excellent candidate for a script.  Something more like ImagesPlus's Auto Imageset Processing would serve as an excellent model. 

Mike