Warning: No correlation between the master dark and target frames

[kelvinator]

hello,
When calibrating the flats with their bias and darks get this error message:

****************************************************************************
Calibrating target frame 20 of 21
Loading target frame:
D:/HELIX/FLATS/IMG_5433.CR2
Timestamp: Sat Jul 23 21:16:23 2011
Camera: Canon EOS 50D
Owner: Luis Martinez Martin
ISO speed: 800
Shutter: 1/256.0 sec
Aperture: f/1.$
Focal length: 0.0 mm
Embedded ICC profile: no
Number of raw images: 1
Thumb size:  4752 x 3168
Full size:   4832 x 3228
Image size:  4770 x 3177
Output size: 4770 x 3177
Raw colors: 3
Filter pattern: RGGBRGGBRGGBRGGB
Daylight multipliers: 2.152106 0.923892 1.096658
Camera multipliers: 2411.000000 1024.000000 1188.000000 1024.000000

Invoking: dcraw -D -k 0 -t 0 -o 0 -4
Decoding Canon EOS 50D file (4770x3177 pixels, ISO=800, Exposure=1/256s): 100%
Loading raw image: 100%

Writing output file: D:/HELIX/FLATS/pixi/IMG_5432_c.fit
Dark scaling factors:
k0 = 0.001
** Warning: No correlation between the master dark and target frames.
k1 = 0.000
** Warning: No correlation between the master dark and target frames.
k2 = 0.001
** Warning: No correlation between the master dark and target frames.
Writing FITS image: 32-bit floating point, 3 channel(s), 4770x3177 pixels: 100%
****************************************************************************

 I'm using the tutorial Vicent Peris listed on this page:
http://pixinsight.com/tutorials/master-frames/en.html

I make the darks, bias and flats without moving the camera.

 Any ideas?

Regards,
Luis

-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

Buenas,

Cuando calibro los flats, con Pixinsight 1.7, con sus darks y bias correspondientes me aparece el siguiente error:

****************************************************************************
Calibrating target frame 20 of 21
Loading target frame:
D:/HELIX/FLATS/IMG_5433.CR2
Timestamp: Sat Jul 23 21:16:23 2011
Camera: Canon EOS 50D
Owner: Luis Martinez Martin
ISO speed: 800
Shutter: 1/256.0 sec
Aperture: f/1.$
Focal length: 0.0 mm
Embedded ICC profile: no
Number of raw images: 1
Thumb size:  4752 x 3168
Full size:   4832 x 3228
Image size:  4770 x 3177
Output size: 4770 x 3177
Raw colors: 3
Filter pattern: RGGBRGGBRGGBRGGB
Daylight multipliers: 2.152106 0.923892 1.096658
Camera multipliers: 2411.000000 1024.000000 1188.000000 1024.000000

Invoking: dcraw -D -k 0 -t 0 -o 0 -4
Decoding Canon EOS 50D file (4770x3177 pixels, ISO=800, Exposure=1/256s): 100%
Loading raw image: 100%

Writing output file: D:/HELIX/FLATS/pixi/IMG_5432_c.fit
Dark scaling factors:
k0 = 0.001
** Warning: No correlation between the master dark and target frames.
k1 = 0.000
** Warning: No correlation between the master dark and target frames.
k2 = 0.001
** Warning: No correlation between the master dark and target frames.
Writing FITS image: 32-bit floating point, 3 channel(s), 4770x3177 pixels: 100%
****************************************************************************

No muevo la cámara cuando hago estas tomas, así que no entiendo el mensaje de que no coinciden las tomas.
Para el calibrado y apilado estoy usando el tutorial de Vicent Peris.

¿Alguna idea de lo que estoy haciendo mal?


Un saludo,
Luis

[Philip de Louraille]

Please see this thread for an answer:  http://pixinsight.com/forum/index.php?topic=2528.msg17025#msg17025

[Juan Conejero]

Hi Luis,

Are you subtracting your master bias frame from your individual flat frames *and* from your master dark frame? Failure to subtract bias correctly is a common cause for these errors.

[Cyclop_si]

H...*and* from your master dark frame...

Juan,

If I follow this tutorials http://pixinsight.com/tutorials/master-frames/en.html, there is no subtracting master bias while creating master dark frame, just for flat frames.
What is correct procedure?

[Juan Conejero]

Hi,

There are three possibilities:

(1) You have simply integrated the individual dark frames to generate the master dark frame. In this case the master dark frame does have a bias pedestal. This is the most usual procedure, and also the one shown in Vicent's tutorial.

(2) After (1), you have calibrated the master dark frame with ImageCalibration to subtract the master bias frame. In this case the master dark frame does not have a bias pedestal. 

(3) You have calibrated the individual dark frames by subtracting the master bias frame from each of them, before integrating them to generate the master dark frame. In this case the master dark frame does not have a bias pedestal, as in (2). This procedure is atypical.

When you calibrate the individual flat frames:

- If (1) is true, then you have to check the Calibrate check box for the Master Dark section --otherwise the bias wouldn't be subtracted.

- If either (2) or (3) are true, then you must leave the Calibrate check box unchecked in the Master Dark section of ImageCalibration --otherwise you would subtract the bias twice.

Most dark frame optimization problems (such as 'no correlation') happen because the bias level is not correctly subtracted from one or more calibration frames; usually from the master dark frame.

Let me know if this helps.

[Cyclop_si]

Juan,

Thanks for explanation.

This explain why  in Vincent's tutorial, Figure 2, Callibration is checked under Master Dark section.
This brings another question to me. What does checked Calibration option under Master Bisa stands for? It does not make sense to calibrate Master Bias with Master Bias to me, therefore this must be something else...

And if folowing option (1) while doing Dark Frames, by chosing Calibrate within Master Dark Section, what is appropiate selection of Calibration checks later on, while Calibrating Light frames?

[kelvinator]

Hello,

Thanks Philip, sorry for not having read the previous thread. Should have looked before asking.

Juan, I subtract the master bias and master dark of the individual flats. On the Image calibration screen I have master bias with calibrate ticked and master dark with calibrate and  optimize ticked, optimization window 1024, Detect CFA.
How should subtract the bias correctly?

Or should first calibrate the flat with the dark and then do the same with bias.

I follow this tutorial http://astrosurf.com/astronosur/pixinsight/preprocessing-1.htm

Anyway, I'll try to uncheck optimize and see what happens. As they say in another thread.

Thanks,
Luis

[Juan Conejero]

It does not make sense to calibrate Master Bias with Master Bias to me, therefore this must be something else...

Indeed The ImageCalibration tool in PixInsight supports calibration with overscan regions. An overscan region is a small area at one edge of the CCD sensor that is not exposed to light. Overscan regions are used to gather additional signal corrections that are applied by subtraction, just as the normal bias (although there is some controversy among our team as for applying overscan as multiplicative corrections). In the case of multi-sensor CCDs there is a different overscan region for each sensor, and using them is necessary to correct for residual differences between sensors that cannot be fixed with a single bias. Overscan corrections are applied to all frames, including biases.

[Juan Conejero]

Anyway, I'll try to uncheck optimize and see what happens. As they say in another thread.

If you do that you'll lose dark frame optimization, which is one of the best features of our image calibration tools. Dark frame optimization minimizes noise induced by dark frame subtraction in your calibrated frames. However, disabling dark frame optimization can be useful to diagnose the problem.

What I'd do is to identify the cause of the problem. The problem can originate either during the acquisition phase (unmatched bias, dark and flat frames for some reason) or during calibration. Let's assume the data have been acquired correctly, so we should focus on the calibration phase.

I subtract the master bias and master dark of the individual flats.

How did you generate the master dark frame? Have you just integrated individual dark frames (option 1) or have you calibrated the master dark (option 2)?

[kelvinator]

Hello,

I use the first option.

First, convert the .cr2 files to .fit with the script "BatchFormatConversion."

Then, I put the following information in ImageIntegration tool:

Image integration
Combination --> Average
Normalization --> No normalization
Weights --> Don't care
Check --> generate integrated image

Pixel Rejection (1)
Algorithm--> winsorized sigma clipping
Normalization --> No normalization
Check  all-->  Generate rejection maps, Clip low/high pixel and range

Pixel Rejection (2)
Sigma low --> 4.0
Sigma high --> 3.0

range low --> 0
range high --> 0.98

Regards,
Luis