[Insight-developers] Image as an OrientedImage Progress

[kent williams]

There is a similar problem in the Analyze ImageIO, and it's rather baffling
that it doesn't show up in e.g. The NIfTI ImageIO.

I'm not sure about how to fix this, but the thing about 2D images is that
they always have an implied third dimension, which is perpendicular to the
acquisition plane.  The ideal situation would be this: if ITK reads a 2D
image, it should embed it correctly in a 3D volume. As you point out, that's
how DICOM works.

I can think of only a couple ways to fix this; one easy and probably wrong
in ways that won't matter a large percentage of the time, and one hard and
correct.

Easy: Stop throwing the exception, and silently allow degenerate dir cosines
in 2D.
Hard: Make 3 the minimum size for a direction cosine.

The 'hard' solution means these things:

1. Verify that every ImageIO class fills out 3 vectors even in 2D
2. Look for and verify that every class in the library, every example
program, and every InsightApplications program, that diddles dir cosines
directly does something reasonable in the 2D case.

As far as programs by Insight Users go, just going to OrientedImage as the
default will break a few of them.

On 9/16/08 9:57 AM, "Bill Lorensen" <bill.lorensen at gmail.com> wrote:

> Here is the problem with the remaining failing tests. This issue has
> been raised before.
> See http://public.kitware.com/Bug/view.php?id=5573
> 
> There are really two "dimensions" of an image.
> 
> 1) ImageDimension is the number of dimensions in the image container,
> 1, 2, 3, ...
> 2) I'll call it SpatialDimension, the number of dimensions in the
> coordinate system of the image. This dimension is the dimension used
> for origin, spacing and the direction.
> 
> For example, in general, DICOM images have an image dimension of 2,
> yet the image position patient and directions are of dimension 3.
> Analyze images have the same issue. And I'm sure nrrd's also.
> 
> In the failing tests, single dicom images are selected and the direction
> 1 0 0
> 0 0 -1
> 0 -1 0
> 
> The current logic in ImageFileReader, simply truncates the direction to:
> 1 0
> 0 0
> which is singular.
> 
> So... we need some further thought about this problem.
> 



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