taskGNU Astronomy Utilities - Tasks: task #14140, Using Gaussian sigma instead of...


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task #14140: Using Gaussian sigma instead of quantile for initial thresholds

Submitter:  Mohammad Akhlaghi <makhlaghi>
Submitted:  Mon 29 Aug 2016 09:28:28 AM UTC
Should Start On:  Sun 28 Aug 2016 03:00:00 PM UTC Should be Finished on:  Sun 28 Aug 2016 03:00:00 PM UTC
Category:  NoiseChisel Priority:  5 - Normal
Item Group:  Enhancement Status:  Need Info
Privacy:  Public Assigned to:  makhlaghi
Percent Complete:  0% Open/Closed:  Open
Effort:  0.00

Mon 29 Aug 2016 09:28:28 AM UTC, original submission:  

The user specifies the threshold values that are applied to the convolved image in NoiseChisel as quantiles. Quantiles are a non-parametric (model-agnostic) measures to specify a point in a distribution. Once you assume a distribution, then the quantile can be translated to the distribution parameters through the inverse of the cumulative distribution function, or the Quantile function. This was one of the main reason we adopted this low-level, non-parametric scale for the user to specify the threshold.

However, the threshold is only found when the median and mode of the distribtuion are approximately equal (signal has not skewed the noise distribtion significantly). In the context of observational noise, the only relevant distribution (that I can think of right now) that has this property is the Gaussian distribution.

Since astronomers are more accustommed to think parametrically (and most commonly with a Gaussian distribution), it might be better to specify these initial thresholds in units of the Gaussian sigma and not quantile.

I am still considering which one to choose and I might be missing some points, so I am opening this task as a discussion point to find the best way forward.

Mohammad Akhlaghi <makhlaghi>
Group administrator


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