[Insight-developers] Reading vector images

[Stephen R. Aylward]

Hi,

I think we need to think about this more for consistency.

I've traditionally distinguished multi-component images from images of 
vectors.   MetaImage supports multi-component images - that is, an image 
of float with multiple channels per pixel.  Versus an image of float_arrays.

MetaImage has been working for multi-channel images perhaps it has been 
broken recently, but I know it has worked in the past ai-is.

If you make changes, please ensure backward compatibility with what has 
been working in the past.   We and others have been using it by 
by-passing itk's IO classes and using MetaIO direct.

Thanks,
Stephen

Miller, James V (Research) wrote:

>Okay.
>
>I have part of this working now. There was a minor error in the MetaIO
>object wrt to setting ComponentType verses setting PixelType for arrays.
>
>I need to go back and check whether MetaIO writes pixel type in its header
>as META_FLOAT_ARRAY when writing vector images.  I may have editted a  
>meta header by hand to change a META_FLOAT to a META_FLOAT_ARRAY.
>
>However, most of bug is in the ImageFileReader and ImageIOBase. My current
>solution relies on the memory layout for a Vector<T, N> being equivalent to
>the
>memory layout of an array T[N].  If we can assume this, then I have most
>of the trivial case working (I was able to read a meta image with 2D
>vectors).
>
>One hurdle is going to be if a file has vectors of floats and the reader is
>asked to produce a vector of ints.  I'll need to modify DoConvertPixelBuffer
>to handle this.
>
>Interesting that we have a number of examples that read vector images.  What
>file formats were these tested on?
>
>Jim
>
>
>
>-----Original Message-----
>From: Luis Ibanez [mailto:luis.ibanez at kitware.com]
>Sent: Wednesday, May 12, 2004 7:10 PM
>To: Miller, James V (Research)
>Cc: Insight-developers (E-mail); Julien Jomier
>Subject: Re: [Insight-developers] Reading vector images
>
>
>
>Hi Jim,
>
>Yes, this is a known bug in the MetaImage reader.
>
>  http://www.itk.org/Bug/bug.php?op=show&bugid=580&pos=12
>
>Although, as you pointed out, the error may actually
>be in the ImageFileReader<> class.
>
>
>If you have any hints of how to solve it,
>please go ahead   :-)
>
>
>Your suggestion seem to be in the right direction.
>We certainly have a lot more types defined in
>
>
>          ImageIOBase::SetPixelType()
>
>that in
>
>          ImageIOBase::GetPixelType()
>
>
>They should probably be made symmetrical...
>
>
>
>   Luis
>
>
>
>
>------------------------------------
>Miller, James V (Research) wrote:
>
>  
>
>>I just tried to read an image of two component vectors into ITK using 
>>the Meta format.
>> 
>>I get all zeros.
>> 
>>It looks to me that in ImageFileReader::GenerateData() there is a test for
>> 
>>      m_ImageIO->GetPixelType() == typeid(TOutputImage::PixelType)
>> 
>>TOutputImage::PixelType should be Vector<float, 2>
>> 
>>m_ImageIO->GetPixelType() returns float
>> 
>>The above check for equality fails and a data conversion occurs.  The 
>>result is all zeros.
>> 
>>It looks as though people have asked this on the list before but I did 
>>not find a response.
>>I seem to recall people reading vectors as RGB pixels.
>> 
>>Perhaps if I add a GetPixelType() method to MetaImageIO that checks the 
>>m_PixelType to be VECTOR?
>> 
>> 
>> 
>>
>>*Jim Miller*
>>*/_____________________________________/*
>>/Visualization & Computer Vision//
>>/GE Research/
>>/Bldg. KW, Room C218B/
>>/P.O. Box 8, Schenectady NY 12301/
>>
>>//_millerjv at research.ge.com <mailto:millerjv at research.ge.com>_/
>>
>>/_james.miller at research.ge.com_/
>>/(518) 387-4005, Dial Comm: 8*833-4005, /
>>/Cell: (518) 505-7065, Fax: (518) 387-6981/
>>
>> 
>>    
>>
>
>
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>  
>


-- 
===========================================================
Dr. Stephen R. Aylward
Associate Professor of Radiology
Adjunct Associate Professor of Computer Science and Surgery
http://caddlab.rad.unc.edu
aylward at unc.edu
(919) 966-9695