[Insight-users] Question on itk::ResampleImageFilter for up and downsampling images

[Bill Lorensen]

What version of itk are you using? Prior to itk 3.16 there was an
issue with the location of sample points. IN 3.16 we changed the
default for ITK_USE_CENTERED_PIXEL_COORDINATES_CONSISTENTLY to be ON.
This made itk consistent with the behavior described in the software
guide. It also corrected the 1/2 pixel offset you are seeing when
down/up sampling.

If you are using 3.14, you can set
ITK_USE_CENTERED_PIXEL_COORDINATES_CONSISTENTLY ON when you run cmake.

Bill

On Thu, Dec 3, 2009 at 9:49 AM, Lodron, Gerald
<Gerald.Lodron at joanneum.at> wrote:
>
>
> Hello,
>
> I want to write a code to reduce/increase the resolution of an image and i am using the itk::ResampleImageFilter. The code works fine but there is one small problem: When i compare the original and the resampled image with a checkerboard i see that the images are not registered any more (so there must be a problem with the origin). How should i set the origin? Here my code:
>
> Input:
>
> Int *iDownsampleFactor;                                 // = e.g. {2,0.5,4};
> Itk::OrientedImage<PixelType ,3>::Pointer image;
>
> Code:
>
> Typedef itk::ResampleImageFilter<InputImageType, OutputImageType, InterpolationPrecisionType> ResampleType;
>
> ResampleType::Pointer  resampler = ResampleType::New();
>
> OutputImageType::SpacingType                    Spacing;
> OutputImageType::PointType                      Origin;
> OutputImageType::DirectionType          Direction = image->GetDirection();
> OutputImageType::SizeType                       Size;
> OutputImageType::RegionType::IndexType  Index = image->getLargestPossibleRegion().GetIndex();
>
> For (int i=0; i<3; i++)
> {
>        Spacing[i] = image->GetSpacing()[i] * iDownsampleFactor[i] ;
>        Origin[i] = image->GetOrigin()[i];//????????????????????
>        Size[i] = image->GetLargestPossibleRegion().GetSize()[i]/iDownsampleFactor[i] ;
> }
>
> Resampler->SetInput(image);
> resampler->SetOutputSpacing( Spacing );
> resampler->SetOutputOrigin(  Origin  );
> resampler->SetOutputDirection(  Direction  );
> resampler->SetSize( Size );
> resampler->SetOutputStartIndex(  Index );
>
> Output = resampler->GetOutput();        //Wrong alignment/registration to input
>
> Best regards
>
>
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