[ITK Community] Bug in DefaultVectorPixelAccessor

[Jan Ehrhardt]

Hi Matt,

yes, I currently use the ITK iterators, but I have the following problem.

Standard code looks like:

itk::ImageRegionIterator<ImageType1> it( radius, myImage, region );
itk::ImageRegionIterator<ImageType2> featureIt1( radius, featureImage1, 
region );
itk::ImageRegionIterator<ImageType3> featureIt2( radius, featureImage2, 
region );

it.GotoBegin();
featureIt1.GotoBegin();
featureIt2.GotoBegin();

while(!it.IsAtEnd())
{
    // do some complicated processing stuff with or without feature1 
and/or feature2

   ++it;
   ++featureIt1;
   ++featureIt2;
}

I only know at runtime, whether featureImage1 and/or featureImage2 are 
available. If
featureImage1 or featureImage2 is NULL, a segmentation fault occurs.

Therefore, I have currently implemented:

itk::ConstNeighborhoodIterator<ImageType1> it( radius, myImage, region );

it.GotoBegin();

while(!it.IsAtEnd())
{
    currentIndex=it.GetIndex();
    if( featureImage1.IsNotNull())
    {
         // use featureImage1->GetPixel(currentIndex) to process feature 1
     }
     if( featureImage2.IsNotNull())
    {
         // use featureImage2->GetPixel(currentIndex) to process feature 2
    }

    // do some other stuff

   ++it;
}

The Image::GetPixel() method is quite time-consuming and therefore I 
look for a more efficient method
to implement this code (without writing four different versions).

Any suggestions?

Best regards,
Jan

On 03/11/2014 06:12 AM, Matt McCormick wrote:
> Hi Jan,
>
> To iterator through an Image or VectorImage, use the Iterators as 
> described in the Software Guide [1]
>
> HTH,
> Matt
>
> [1] http://itk.org/ItkSoftwareGuide.pdf
>
>
> On Thu, Mar 6, 2014 at 8:23 AM, Jan Ehrhardt 
> <ehrhardt at imi.uni-luebeck.de <mailto:ehrhardt at imi.uni-luebeck.de>> wrote:
>
>     Hi folks,
>
>     I want to iterate through a vector image without an iterator. My
>     approach was:
>
>         MultiChannelImageType::AccessorType accessor =
>     pImage->GetPixelAccessor();
>         MultiChannelImageType::InternalPixelType* pBuffer =
>     pImage->GetBufferPointer();
>
>         for( OffsetValueType i = from; i < to; ++i )
>         {
>             vecPixel = accessor.Get(*pBuffer, i);
>         }
>
>     but the results are not correct (see bug(?) below). If the bug(?)
>     in DefaultVectorPixelAccessor is corrected ( m_OffsetMultiplier =
>     l ) the behaviour of standard itk iterators change. I assume, I
>     don't understand the parameters of
>     DefaultVectorPixelAccessor::Get() correctly.
>     How can I use the DefaultVectorPixelAccessor correctly?
>
>     best,
>     jan
>
>
>     On 03/06/2014 12:25 PM, Jan Ehrhardt wrote:
>
>         Hi folks,
>
>         there is a bug in DefaultVectorPixelAccessor (ITK 4.4.0):
>
>           void SetVectorLength(VectorLengthType l)
>           {
>             m_VectorLength = l;
>             m_OffsetMultiplier = ( l - 1 );
>           }
>
>           DefaultVectorPixelAccessor(VectorLengthType l)
>           {
>             m_VectorLength = l;
>             m_OffsetMultiplier = l - 1;
>           }
>
>         OffsetMultiplier should be m_OffsetMultiplier = l;
>
>         Best regards,
>         Jan
>
>
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