# 3D multi-modal medical image registration using user defined function for similarity metric computation

**URL:** https://discourse.itk.org/t/3d-multi-modal-medical-image-registration-using-user-defined-function-for-similarity-metric-computation/5064
**Category:** Beginner Questions
**Tags:** registration, python, simpleitk
**Created:** [June 7, 2022, 10:09am UTC](https://discourse.itk.org/t/3d-multi-modal-medical-image-registration-using-user-defined-function-for-similarity-metric-computation/5064 "2022-06-07T10:09:04Z")
**Posts on this page:** 1
**Showing post:** 3

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### Author: ![debapriya](https://discourse.itk.org/letter_avatar_proxy/v4/letter/d/bc79bd/32.png) [@debapriya](https://discourse.itk.org/u/debapriya)
#### Post date: [June 9, 2022, 5:54am UTC](https://discourse.itk.org/t/3d-multi-modal-medical-image-registration-using-user-defined-function-for-similarity-metric-computation/5064/3 "2022-06-09T05:54:01Z")

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Thank you @dzenanz !! Following your advice and the [chain of conversation you mentioned](https://discourse.itk.org/t/changes-in-itk-mattes-mutual-information-metric/2353), I have found that the computation of mutual information is happening [here](https://github.com/InsightSoftwareConsortium/ITK/blob/b5fdb855a01cd1b223e4b8ecac050fb5e3e2f46c/Modules/Registration/Metricsv4/include/itkJointHistogramMutualInformationImageToImageMetricv4.hxx#L332-L384). Please correct me if I am wrong.

Now I want to run this code, preferably in debugger mode, and modify it. How can I do that? My knowledge in C++ is limited to high school level.

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