[Insight-users] MattesMutualInformation questions

[gabri]

Hi all,
I would like to understand how to fine tune an Affine3DRigid
Registration using MattesMutualInformationImageToImageMetric.
The simple question is :
I suppose that in theory the MI final value would be  maximized, for a
correct registration result.
But in my code the final value is minor than the first step of the
itaration process.
first ->
0   -0.190391   [0.995462, -0.00157196, 0.00313902, 0.000640376,
1.00341, -0.00225071, 0.000649128, -0.00112494, 0.997894, -3.2308,
-4.89763, -18.4037] AffineAngle: 0.0634048


last ->
80   -0.26143   [0.993057, -0.00753589, 0.0122628, 0.000674591, 1.00105,
0.00183965, 0.00413924, -0.005144, 0.991511, -3.08394, -4.94793,
-18.5664] AffineAngle: 0.234475

why my values are minor than zero? is this correct ?
The images that my code produce are fine coregistered but i could not
understand (search in the itk handbook and also in mailing list's
previous post) why the values are negative...

Best reguards ,
Gabriele

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