Warning Using Bias subtracted master darks is considered bad practice?

[UlteriorModem]

I am suddenly getting this error message.

"Warning, Using bias subtracted master darks is considered bad practice".

The master dark is NOT bias subtracted. In fact it is not 'calibrated' in any manner.

The only thing I can think of is that the master dark is a couple of months old and there may have been some changes since the recent updates?

For now I ignore the warning and move on. But do I need a whole new set of master darks and bias?

[Juan Conejero]

The latest versions of the WBPP script include a new Calibrate master darks option. This option should normally be enabled, i.e. checked, as it is by default.

"Warning, Using bias subtracted master darks is considered bad practice".

You have inadvertently disabled the Calibrate master darks option. When you did that, the script showed you a warning message describing the potential problems associated with pre-calibrated master dark frames, as well as the reasons why using them is generally a bad idea.

For now I ignore the warning and move on.

Please never do that. Warning messages are always shown for good reasons. Never ignore them unless you are sure that you understand what's happening and the associated risks.

If you have performed a preprocessing task with the Calibrate master darks option disabled, and your master dark is not pre-calibrated, then the result is completely wrong and you'll have to repeat the entire process with this option enabled.

See Bernd's calibration guide for an excellent and detailed discussion on this topic.

[Geoff]

I don't understand this.  Surely a master dark is one that has already been calibrated--maybe several months previously. So what exactly does the calibrate master darks option actually do?
Geoff

[bulrichl]

Hi Juan,

I am assuming that the MasterDark is not pre-calibrated with the MasterBias, as recommended in Vicent's tutorial https://www.pixinsight.com/tutorials/master-frames/ . This warning should only appear when the user tries to disable 'Calibrate master darks' while dark frame optimization is used.

However, it should NOT appear when dark frame optimization is not used. We don't need to subtract the MasterBias from both the light frame and the MasterDark -- that is unnecessary. In this case a MasterBias is not needed at all for light frame calibration.

Bernd

[UlteriorModem]

Yes the error message goes away if you select calibrate master darks.

Must have changed that at some point, or the script changed.

[bulrichl]

Hi Juan,

the issue of the OP is not yet fixed:

When dark frame optimization is not used AND neither bias frames nor a MasterBias is loaded AND 'Calibrate master darks' is deselected, NO warning should appear. This setting results in a correct light frame calibration, using either the not pre-calibrated MasterDark or integrating the dark frames to the not pre-calibrated MasterDark and then using it.

Bernd

[Juan Conejero]

When dark frame optimization is not used AND neither bias frames nor a MasterBias is loaded AND 'Calibrate master darks' is deselected, NO warning should appear.

This is true for the '... is considered bad practice' diagnostics warning message. We'll try to improve generation of this warning in a future version of WBPP.

It is important to point out, however, that warning messages are not 'enemies' of the user, or something that we show to complicate things. Warnings are generated to provide useful information that can help prevent serious errors, even if a particular warning message can be unjustified or excessive under certain specific conditions, as happens in this case. An informed user should always interpret warnings as helpers, not as problems. I always prefer to show too many warnings instead of taking the risk to show too few. Other software packages prefer to hide everything that can sound problematic, but this is not the philosophy of PixInsight.