# Derivation of mutual information in EMMA algorithm for image alignment

**URL:** <https://discourse.itk.org/t/derivation-of-mutual-information-in-emma-algorithm-for-image-alignment/3180>\
**Category:** Algorithms\
**Tags:** registration\
**Created:** [June 12, 2020, 1:51pm UTC](https://discourse.itk.org/t/derivation-of-mutual-information-in-emma-algorithm-for-image-alignment/3180 "2020-06-12T13:51:01Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Amey\_Joshi](https://discourse.itk.org/user_avatar/discourse.itk.org/amey_joshi/32/1539_2.png) [@Amey\_Joshi](https://discourse.itk.org/u/Amey_Joshi)\
**Post date:** [June 12, 2020, 1:51pm UTC](https://discourse.itk.org/t/derivation-of-mutual-information-in-emma-algorithm-for-image-alignment/3180/1 "2020-06-12T13:51:01Z")

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This is a question about the derivative of the mutual information between two images with respect to a transformation between them. It appears in one of Paul Viola’s papers that introduced this concept for the first time. I have asked this question on DSP stack exchange but I could not get enough attention to it. Therefore, I bring the question to this group. In order to avoid repetition, I merely give a [link](https://dsp.stackexchange.com/questions/67946/derivative-of-mutual-information-in-emma-algorithm-for-image-alignment) to the quest on Stack Exchange.

Kindly let me know if anyone has a piece of advice about the expression.

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**Author:** ![dzenanz](https://discourse.itk.org/user_avatar/discourse.itk.org/dzenanz/32/1093_2.png) [@dzenanz](https://discourse.itk.org/u/dzenanz)\
**Post date:** [June 12, 2020, 1:56pm UTC](https://discourse.itk.org/t/derivation-of-mutual-information-in-emma-algorithm-for-image-alignment/3180/2 "2020-06-12T13:56:55Z")

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@hjmjohnson might have an answer.