[Insight-users] Computing the metric value?

[Luis Ibanez]

Hi Motes,

You are right,

In that sentence of the ITK Software Guide, the expression
"transformed moving image" is used in a comparative sense.


It is true that the Metric doesn't explicitly transforms the Moving
image to the coordinate system of the Fixed image.

However,

It maps every pixels of the Fixed Image (or the FixedImageRegion
to be precise) to the coordinate system of the Moving image, and
then interpolate values there, just in the same way that the Resample
Image filter would do during a resampling process.

Therefore, for the purpose of explaining what the Metric does, the
sentence is still correct, even though the actual mechanism of
computation of the metric is not a explicit resampling of the Moving
image.


     Regards,


            Luis


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On Wed, Nov 11, 2009 at 5:50 PM, motes motes <mort.motes at gmail.com> wrote:
> In the itkSoftwareGuide page 415 it says:
>
> "In ITK, itk::ImageToImageMetric objects quantitatively measure how
> well the transformed moving
> image fits the fixed image by comparing the gray-scale intensity of the images."
>
>
> I don't understand the term "transformed moving image". As I
> understand the moving image is never transformed.
> Actually its the pixels in the fixed image that is transformed based
> on the following steps in the metric:
>
>
> 1) First the intensity value of the current point in the fixed image
> is looked up:
>
>                      fixedValue = I(Fp)
>
> 2) Next the current point in the fixed image is transformed using the
> current parameters:
>
>                     transformedPoint = T(Fp)
>
> 3) Now this transformed point is feed to the interpolator connected to
> the moving image:
>
>                     movingValue =
> movingImage->interpolator->Eval(transformedPoint)
>
> 4) The difference:
>
>                     diff += movingValue - fixedValue
>
> is computed.
>
>
> Therefore the sentence from the itkSoftwareGuide to my understand should be:
>
> "In ITK, itk::ImageToImageMetric objects quantitatively measure how
> well the intensity
> in the moving image at the transformed fixed coordinates fits the
> intensity in the non-transformed
> fixed image by comparing the gray-scale intensity of the images."
>
> Or am I missing the point here?
>
>
>
>
>
>
> In the image registration method the metric is used to compare how
> identical the fixed image is with the tr
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