[Insight-developers] VectorImage: and contiguous memory assumption

[Karthik Krishnan]

Yes. You can (currently) access the block like that and you will have the
following memory organization, for the following images


  x1 y1 x2 y2 x3 y3 x4 y4.... xN yN



   Image< Vector< T, 2 >, 3 >

and

   VectorImage< T, 3 >
   vimage->SetVectorLength(2);


where N is the number of pixels.

Yes, itk::Vector does not have any mmeber vars other than data

thx
--
karthik
On Tue, Apr 12, 2011 at 2:59 AM, M Stauffer (V) <mstauff at verizon.net> wrote:

> Hi Luis,
>
> How do we access the memory of an Image< Vector, Dimension > object as a
> contiguous block?
>
> When I use
> Image<Vector,Dimension>::GetPixelContainer::GetBufferPointer(), I get an
> array of Vector pointers, not a pointer to a block of pixel elements.
>
> In a simple test I can get a contiguous block of properly-ordered pixel
> elements like this:
>
> Image<Vector<ValueType, VecDim>, Dim>::PixelContainer container =
> image->GetPixelContainer();
> ValueType* buffer =
> reinterpret_cast<ValueType*>(container->GetBufferPointer() );
>
> But is this safe to rely on? That the memory will always be contiguous
> and ordered? I take it that itkVector doesn't have any member variables
> other than the data, otherwise this wouldn't work.
>
> Thanks.
>
> Cheers,
> Michael
>
> >Hi Brian,
> >
> >
> >The memory layout of the image type
> >
> >         itk::Image< Vector , Dimension >
> >
> >for
> >
> >          Vector = itk::Vector< float, 2 >
> >
> >is:
> >
> >      x1 y1 x2 y2 x3 y3 x4 y4.... xN yN
> >
> >
> >Where N is the number of pixels.
> >
> >
> >So,
> >the components of a pixel are grouped
> >contiguously in memory.
> >
> >
> >      Luis
> >
> >
> >--------------------------
> >On Tue, Mar 29, 2011 at 4:09 PM, brian avants <stnava at gmail.com> wrote:
> >> luis
> >>
> >> do you by chance know the memory layout for the
> >>
> >> itk::Image< Vector , type >  ?
> >>
> >> is it
> >>
> >> x1 x2 x3 y1 y2 y3
> >>
> >> or
> >>
> >> x1 y1 x2 y2 x3 y3
> >>
> >> ?
> >>
> >> brian
> >>
> >>
> >>
> >>
> >> On Wed, Mar 23, 2011 at 8:49 PM, Luis Ibanez
> ><luis.ibanez at kitware.com> wrote:
> >>> Brad, Nick,
> >>>
> >>> It turned out that I was wrong about the internal
> >>> memory organization of the VectorImage class.
> >>>
> >>> Looking closely at the code, particularly the
> >>> GetPixel, SetPixel methods of this class,
> >>> and after checking with Karthik (who actually
> >>> implemented this class), it turns out that the
> >>> memory organization is actually
> >>>
> >>>
> >>> 1) All the components of pixel 1, followed by
> >>> 2) All the components of pixel 2, followed by
> >>> 3) All the components of pixel 3, followed by
> >>> 4) All the components of pixel 4, followed by
> >>>
> >>> and so on...
> >>>
> >>>
> >>> Instead of what I wrongly thought:
> >>>
> >>>
> >>> 1) All the pixels of component 1, followed by
> >>> 2) All the pixels of component 2, followed by
> >>> 3) All the pixels of component 3, followed by
> >>>
> >>> and so on...
> >>>
> >>>
> >>>
> >>> So, it makes me wonder if there is a case
> >>> to be made for introducing an image class
> >>> with the second type of memory organization...
> >>>
> >>>
> >>>     Luis
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