[Insight-users] ITK Rigid2DTransform - introduces shearing ?

[Luis Ibanez]

Hi John,

What is the pixel spacing (along X and Y) of the original image ?


The appearance of shearing may be the result of using PNG files to store
the output images. PNG doesn't carry along the pixel information of your
image.  Therefore, when you display it with naive viewers, the proportions
of the image may get distorted, an a appearance of shearing may be
observed.

You may want to make sure that you use both

   (A)   a file format   and
   (B)   an image viewing program

that supports (takes into account) image spacing.

Common combinations are:


   (A)  MetaImage
   (B)  The ImageViewer tool in InsightApplications


Regards,


         Luis


-----------------------------------------------------------------------------------------------
On Wed, Jan 27, 2010 at 12:27 AM, John D <john.dz.eis at gmail.com> wrote:
> Dear all,
>
>   When using Rigid2DTransform to transform an image, I seem to be getting a
> shearing of the result. I was actually trying to compare the results between
> an ITK prototype and an IPP implementation of an algorithm when I started
> noticing the difference. Please see the attached images. I drew in a grid
> into the image to see what was causing the difference and it seems like the
> image I obtain by transforming using the Rigid2DTransform has a shear in it
> while the IPP one does not have the shear as expected. All I am trying to do
> here is to rotate the image by 30 degrees around the center of the image.
> Any thoughts on what could be going wrong ?
>
> This is the code I am using for the ITK transform function
>
>     typedef itk::ResampleImageFilter< enFaceImageType, enFaceImageType >
> ResampleFilterType;
>     // A resampling filter is created and the image is connected as its
> input:
>     ResampleFilterType::Pointer resampler = ResampleFilterType::New();
>     resampler->SetInput( image );
>
>     // Set the transformation according to our input values:
>     typedef itk::Rigid2DTransform< double > TransformType;
>     TransformType::Pointer transform = TransformType::New();
>
>     // Set the parameters of the transform by passing them in an array:
>     typedef TransformType::ParametersType ParametersType;
>     ParametersType manualParameters( transform->GetNumberOfParameters() );
>     manualParameters[0] = dRad;        // Angle
>     manualParameters[1] = xTrans;    // Initial offset in mm along X
>     manualParameters[2] = yTrans;    // Initial offset in mm along Y
>
>     transform->SetParameters( manualParameters );
>
>     TransformType::InputPointType center;
>     center[0] = centerX;
>     center[1] = centerY;
>     transform->SetCenter(center);
>
>     resampler->SetTransform( transform );
>
>
>     // Take sizes from the fixed image, as that is what we are registering
> to:
>     resampler->SetSize( image->GetLargestPossibleRegion().GetSize() );
>     resampler->SetOutputOrigin( image->GetOrigin() );
>     resampler->SetOutputSpacing( image->GetSpacing() );
>     resampler->SetDefaultPixelValue( 0.0 );
>
>
>     if (interpolation==0)
>     {
>         typedef
> itk::NearestNeighborInterpolateImageFunction<enFaceImageType, double >
> InterpolatorType;
>         InterpolatorType::Pointer interpolator = InterpolatorType::New();
>         resampler->SetInterpolator(interpolator);
>     }
>     if (interpolation==1)
>     {
>         typedef itk::LinearInterpolateImageFunction<enFaceImageType, double
>>  InterpolatorType;
>         InterpolatorType::Pointer interpolator = InterpolatorType::New();
>         resampler->SetInterpolator(interpolator);
>     }
>
>     resampler->Update();
>
>     iStatus = EXIT_SUCCESS;
>     return ( resampler->GetOutput() );
>
>
> Thanks,
> John
>
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