[Insight-users] MetaImageIO and vector fields: GetPixelType small bug?

[Stephen R. Aylward]

Hi Tom,

I debated this issue for quite some time, and decided to go with the 
convention that (to me) was closest to what ITK was already doing.

If the image has multiple variates per pixel, it is considered to be a 
multi-channel image, and the element type is the type of each variate. 
In that manner, we can have an RGB image of chars or an RGB image of 
floats as well as a multi-channel image of vectors.   Declaring 
something as multi-channel and the pixel type as vectors defined, in my 
opinion, a multi-channel image in which each channel contains a vector. 
  I'd rather not have redundant information and allow for a more 
flexible design.

In the ideal world, I should determine if a given pixel type is 
representing independent variates or a mathematical vector and from 
there switch between a multi-channel of scalars or a vector pixel 
representation.   However, I am not certain that I would want to enforce 
such typing - sometimes an RGB image considers the channels 
independently and sometimes as a colorspace vector.

I am open to (backward compatible) suggestions for alternatives. 
However, I do believe that multi-channel should not require a vector 
pixel type.

Thanks,
Stephen

Tom Vercauteren wrote:
> Hi all,
> 
> I think I found a small bug in MetaImageIO (ITK 3.0.1).
> 
> I have an mha file with the following header:
> ObjectType = Image
> NDims = 3
> BinaryData = True
> BinaryDataByteOrderMSB = False
> CompressedData = False
> TransformMatrix = -1 0 0 0 -1 0 0 0 1
> Offset = 127.75 145.75 -72.25
> CenterOfRotation = 0 0 0
> AnatomicalOrientation = RPI
> ElementSpacing = 1 1 1
> DimSize = 256 256 181
> ElementNumberOfChannels = 3
> ElementType = MET_FLOAT
> ElementDataFile = LOCAL
> 
> I create an image IO using ImageIOFactory::CreateImageIO and then
> check the pixel type. As expected I see that GetNumberOfComponents
> returns 3 but I also get:
> imageIO->GetPixelType() == itk::ImageIOBase::SCALAR
> 
> I thought I would get  itk::ImageIOBase::VECTOR or
> itk::ImageIOBase::COVARIANTVECTOR.
> 
> Should I file a bug for that or am I missing something here?
> 
> Best regards,
> Tom Vercauteren
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> 

-- 
=============================================================
Stephen R. Aylward, Ph.D.
Chief Medical Scientist
Kitware, Inc. - Chapel Hill Office
http://www.kitware.com
Phone: (518)371-3971 x300