Subframe Selector--does weight influence integration?

[rmaddy]

Please pardon a noob.

I have become familiar with navigating and using the subframe selector script.  What I want to know is whether the assigned weights (or SNRweight) is used during integration, i.e. does a better frame have more influence on the final mix, or are the data simply FYI?

[mschuster]

By default no, not used by ImageIntegration.

SNRWeight is effectively the weight ImageIntegration would use if you were to set the ImageIntegration option Image Integration > Weights to Noise Evaluation and Image Integration > Scale estimator to Average absolute deviation from the median.

To use the script's assigned weight in ImageIntegration you need to do the following in the script:

Set Output > Approved action to Copy.
Set Output > Weight keyword to some value, for example IWEIGHT.
Set Expressions > Weighting to the weighting expression that you want to use.

Then click the script's Output subframes button, which will copy all of the approved frames, including the weight keyword and value in the copy's FITS header.

Then, in ImageIntegration:

Set Image Integration > Weights to FITS keyword.
Set Image Integration > Weight keyword to the weight keyword you are using, eg IWEIGHT.

As an example weighting expression, you might try the expression SNRWeight / FWHM^2. Frames with (1) higher contrast (scale), (2) lower noise, and (3) lower FWHM will tend to be weighted higher. (The squaring of FWHM is a heuristic that in some sense "matches" the squaring of scale and noise in SNRWeight, the later done for technical optimality reasons.)

Thanks,
Mike

[rmaddy]

Ok, I see those steps. 

So, if I understand correctly, following them toggles from the "noise evaluation" weighting routine of the ImageIntegration process to a user defined weighting technique, for example "SNRWeight/FWHN^2" in your scenario.  Either way, there is a weighting of subs during integration--the only choice is whether or not to tweak the subroutine.

Correct?

[mschuster]

Yes. Basically ImageIntegration itself provides some weighting options, the script provides even more options.

[ChoJin]

but the subframeselector doesn't use, as far as i know, the "new" robust and efficient noise estimator to compute the SNR (biweight midvariance and alike)

[mschuster]

Wrong. The script uses exactly the same noise estimator. However, the script uses a scale estimator that is no longer the default. This problem will be corrected eventually.

[ChoJin]

sorry I misused words, I was talking about the scaling estimator