# What is the standard deviation (sigma) used to compute the Hessian in SimpleITK's ObjectnessMeasure
**URL:** https://discourse.itk.org/t/what-is-the-standard-deviation-sigma-used-to-compute-the-hessian-in-simpleitks-objectnessmeasure/822
**Category:** Algorithms
**Tags:** simpleitk
**Created:** [April 3, 2018, 2:04pm UTC](https://discourse.itk.org/t/what-is-the-standard-deviation-sigma-used-to-compute-the-hessian-in-simpleitks-objectnessmeasure/822 "2018-04-03T14:04:38Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@nicoco](https://discourse.itk.org/u/nicoco)
#### Post date: [April 3, 2018, 2:04pm UTC](https://discourse.itk.org/t/what-is-the-standard-deviation-sigma-used-to-compute-the-hessian-in-simpleitks-objectnessmeasure/822/1 "2018-04-03T14:04:38Z")
Hello all,
I’m trying to use the brand new SimpleITK procedural interface to the [ObjectnessMeasureFilter](https://itk.org/SimpleITKDoxygen110/html/classitk_1_1simple_1_1ObjectnessMeasureImageFilter.html).
Since it automatically computes the Hessian Matrix of the image, I’d like to know which sigma value is used for this purpose. If I’m not mistaken, it is a crucial parameter of this filter.
Thanks for your help.
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### Author:  [@blowekamp](https://discourse.itk.org/u/blowekamp)
#### Post date: [April 3, 2018, 2:15pm UTC](https://discourse.itk.org/t/what-is-the-standard-deviation-sigma-used-to-compute-the-hessian-in-simpleitks-objectnessmeasure/822/2 "2018-04-03T14:15:23Z")
There is no sigma. It computes the Hessian directly on the provided image via discrete differences. Simply run a your favorite Gaussian filter before.
I apologize I have a draft of an Insight Journal paper which describe some of these details I need to finish.
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### Author:  [@nicoco](https://discourse.itk.org/u/nicoco)
#### Post date: [April 3, 2018, 2:54pm UTC](https://discourse.itk.org/t/what-is-the-standard-deviation-sigma-used-to-compute-the-hessian-in-simpleitks-objectnessmeasure/822/3 "2018-04-03T14:54:16Z")
I see, thank you for the very quick answer.