[Insight-users] [ITK Community] Why is the Normalized Correlation Metric inverted?

[Matt McCormick]

Hi Jonas,

By convention, many of the optimizers work to minimize the metric they
are given.

Thanks,
Matt

On Sun, Nov 17, 2013 at 5:58 AM, Jonas Beuke <abbo_jonas at gmx.de> wrote:
> Hi all,
>
> I'm comparing images by using itkNormalizedCorrelationImageToImageMetric as
> a similarity metric. As far as I can see it implements exactly the Pearson
> product-moment correlation coefficient except for the line 117 "const
> RealType denom = -1.0 * vcl_sqrt(sff * smm);". This line, as far as I
> understand it, inverts the correlation so -1 is a perfect positive
> correlation between the two images. What is the purpose of this?
>
> Greetings,
> Jonas
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