Author Topic: No correlation between the master dark and target frames?  (Read 6830 times)

Offline dlp

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No correlation between the master dark and target frames?
« on: 2010 November 09 06:46:32 »
Just recently started with the trial and am having lots of problems with my dslr workflow. I've managed to integrate my darks, but when I go to calibrate my lights (which are same attributes), I am getting the following message for each image:

Writing output file: C:/Users/<etcetc>/DSC_2039_c.fit
Dark scaling factors:
k0 = 0.000
** Warning: No correlation between the master dark and target frames.
k1 = 0.000
** Warning: No correlation between the master dark and target frames.
k2 = 0.000
** Warning: No correlation between the master dark and target frames.
Writing FITS image: 32-bit floating point, 3 channel(s), 4310x2868 pixels: 100%

On the calibration screen I have only master dark ticked, with calibrate, optimize, optimization window 1024, Detect CFA

Anyone advise please?

David

Offline Juan Conejero

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Re: No correlation between the master dark and target frames?
« Reply #1 on: 2010 November 09 07:27:23 »
Hi David,

Welcome to PixInsight Forum.

Those warning messages are telling you that the master dark frame you are using has no correlation to the light frame in terms of thermal noise. In other words, if the master dark frame is subtracted from that light frame, then the result will always have more noise than the original. Hence, a zero dark scaling factor is being applied, which is equivalent to not subtracting the master dark frame at all.

The noise evaluation routine implemented in our ImageCalibration tool is very robust, so in general my advice is trusting it. We still haven't seen a practical case were it fails to compute an optimal dark scaling factor.

From the file names on your post I assume you're calibrating DSLR images. Why are not you using bias frames?

Juan Conejero
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Offline cfranks

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Re: No correlation between the master dark and target frames?
« Reply #2 on: 2010 November 09 13:16:30 »
This happens to me with some .fits files when I have the Optimise box checked.  The resulting images are garbage - completely flat background, stars are fully saturated and absolutly no trace of the DSO.  Unchecking Optimise fixes the problem.

Charles

Offline Jack Harvey

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Re: No correlation between the master dark and target frames?
« Reply #3 on: 2010 November 10 15:28:43 »
I have seen this also lately in the new version
Jack Harvey, PTeam Member
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Offline jjk

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Re: No correlation between the master dark and target frames?
« Reply #4 on: 2014 November 11 10:03:35 »
Juan,

If the dark master is not applied to N of M light sub exposures, wouldn't the jot and cold pixels still be unmitigated in the calibrated files?

Best,
John

Offline jkmorse

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Re: No correlation between the master dark and target frames?
« Reply #5 on: 2014 November 11 12:11:47 »
Been seeing this crop up a lot lately in the forum.

You may be running into some FITS incompatibility issues.  I did a lot of research recently on FITS incompatibilities and this issue has been addressed time and again by PI.  Here is the results of my research into old posts on the subject:

Fixing FITS Incompatibilities
If you experience these types of incompatibilities, try the following until you hit on a solution:

First
•   Open the Format Explorer (access under “View > Explorer Windows”)
•   Double click on “FITS”
•   Make sure the top two boxes are checked
       o   “Write scaling keywords . . .”
       o   “Signed Integer images . . .”

Second
•   Where possible, particularly in the Image Calibration tool for Lights, but also with ImageIntegration when creating Master Darks and Master Bias, add the following to the “input hints” line under “Format Hints”:
       o   lower-range 0 upper-range 65535

Third
•   If the above does not work, insert the following in the “input hints” line:
       o   Signed-is-physical

Stop using input hints AFTER you have successfully saved an image after applying a PI tool; i.e, do not use input hints in ImageIntegration after successfully calibrating Light images in PI with the ImageCalibration tool (after first PI application, images are saved in proper PI format (0,1) and no longer need input hints)

For an excellent explanation of what is happening to cause this problem, check out the following threads from Juan Conejero:

http://pixinsight.com/forum/index.php?topic=3118.msg21348
http://pixinsight.com/forum/index.php?topic=3474,msg23973
http://pixinsight.com/forum/index.php?topic=3800.msg26086

Hope that helps,

Jim
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Offline Don

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Re: No correlation between the master dark and target frames?
« Reply #6 on: 2014 November 15 10:13:13 »
Hi David,

I encountered this yesterday when calibrating DSLR raw files, after having used BatchFormatConversion to convert the native format raw files to monochrome FITS.  This happened when calibrating lights in ImageCalibration using a master dark frame, but the BatchPreProcessing script calibrated the same lights with the same master dark without any errors.

Finally I found a solution.  Selecting "Force CFA" for the CFA Pattern Detection method for the master dark frame in ImageCalibration solved the problem.  The default value for CFA Pattern Detection is "Detect CFA", and for some reason this wasn't working with these files.  I don't know if it had something to do with the prior format conversion or not, because I didn't go back and try ImageCalibration with the native DSLR files.  But I'm pretty sure that in the past it wasn't necessary to force CFA detection with raw files converted to FITS (I could be mistaken about this though).

Don