<div dir="ltr"><div style>Hi Lien,</div><div style>You may be seeing the effects of the sampling of the registration region to create the mattes histogram.</div><div style><br></div><div style>If you check the doxygen for the MattesMutualInformationImageToImageMetric and expand the section "public member functions inherited from itk::ImageToImageMetric" you will find a few functions that concern sampling (SetUseAllPixels, SetUseFixedImageIndexes, SetUseSequentialSampling). Importantly, one of these is called ReinitializeSeed(). Take a look at the documentation for that function and it may help answer your question. Briefly:</div>
<div style><br></div><div style>"<span style="color:rgb(0,0,0);font-family:'Lucida Grande',Verdana,Geneva,Arial,sans-serif;font-size:12px;line-height:19px">By nature, this metric is not deterministic, since at each run it may select a different set of pixels. By initializing the random number generator seed to the same value you can restore determinism."</span></div>
<div style><span style="color:rgb(0,0,0);font-family:'Lucida Grande',Verdana,Geneva,Arial,sans-serif;font-size:12px;line-height:19px"><br></span></div><div style><span style="color:rgb(0,0,0);font-family:'Lucida Grande',Verdana,Geneva,Arial,sans-serif;font-size:12px;line-height:19px">Hope this helps,</span></div>
<div style><span style="color:rgb(0,0,0);font-family:'Lucida Grande',Verdana,Geneva,Arial,sans-serif;font-size:12px;line-height:19px">Seth</span></div></div>