[Insight-users] How to concatenate itk transformations

[Stefan Klein]

Hi Jian,


> I checked the insight journal and find two classes related to my
> topic: Combining
> Transforms(http://www.insight-journal.org/dspace/view_item.php?itemid=438)
> and Serial Transformations
> (http://www.insight-journal.org/dspace/view_item.php?itemid=1080).
> However it seems both of them doing the transformations in sequence
> instead of combining them together to get a final form of
> transformation. If the number of the transformations is very big, the
> sequence transformation of image will no doubt downgrade the image
> qualities.

No, this is not true. The image is interpolated only once with these 
transforms. At every point x, the TransformPoint(x) function of the 
SerialTransform/CombinationTransform is called, which calls the 
TransformPoint() functions of the transforms in sequence. When the total 
transformation is computed, the image value is obtained by interpolated 
(so, only once). So, the number of transformations has no impact on the 
image quality.

Kind regards,
Stefan

> 
> Your help will greatly appreciated.
> 
> Jian
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