Hello image registration experts,
I have a question about the mutual information cost metric produced by FLIRT. When I attempt to measure the mutual information of two images using the `measurecost1.sch` schedule file, I get a negative value. I had thought that mutual information was always a positive value. Can someone please point to a reference for the definition of mutual information used in FLIRT?
For instance, running this command:
flirt -in struct_brain -ref gre5-mag -cost mutualinfo -schedule $FSLDIR/etc/flirtsch/measurecost1.sch
Produces this output:
> -0.271626 0.000000 -0.000000 0.000000 0.000000 0.000000 0.000000 1.000000 1.000000 1.000000 0.000000 0.000000 0.000000
>
>
> Final result:
> 1.000000 0.000000 0.000000 0.000000
> 0.000000 1.000000 0.000000 0.000000
> 0.000000 0.000000 1.000000 0.000000
> 0.000000 0.000000 0.000000 1.000000
Which I take to mean that flirt is reporting a mutual information value of -0.271626. Also, using the normmi cost function produces a value of -1.08389, whereas I expected a value between 0 and 1.
Yours,
Andrew Davis
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