[vtkusers] DICOM rescale question

[Mathieu Malaterre]

Sergio,

  vtkImageShiftScale operation is exactly the opposite from what DICOM
mandates (order of operation). If you use vtkGDCMImageReader you
should get your image with proper Rescale Slope/Intercept applied.

HTH

On Thu, Mar 24, 2011 at 6:13 AM, Sergio Aguirre
<sergio.aguirre at gmail.com> wrote:
> Hi everyone.
> I'm sure this has probably been asked before.
> I am reading some DICOM images using ITK and visualizing in VTK.
> Up until now, I have been using vtkImageViewer2 class with no problems at
> all.
> But now, I'd like to create a volume stack of the Dicom images using volume
> rendering and the MIP raycast function (vtkVolumeRayCastMIPFunction). BUT
> the colors are just not right. I see everything a bit gray and see many
> sections that are outside of the image with a value.
> The steps I follow are:
> 1) read in ITK as float, I test the RescaleIntercept (0.0) and RescaleSlope
> (1.0) values.
> 2) export to VTK
> 3) load the images as vtkImageData, I test the Scalar range
> (vtkImage->GetScalarRange) and the values I get are -3024 and 1530 (Im
> pretty sure it should be -1024 1530)
> 4) Since vtkVolume needs unsigned chars, I use vtkImageShiftScale but get
> incorrect image display.
>   vtkImageShiftScale *shift = vtkImageShiftScale::New();
>   shift->SetInput(m_vtkImage);
>   shift->SetScale(255.0/window);
>   shift->SetShift(0.5*window - level);
>   shift->ClampOverflowOn();
>   shift->SetOutputScalarTypeToUnsignedChar();
>   shift->Update();
> How should I be adjusting the scalar range to display it correctly, IF I
> pass the vtkImageData directly to vtkImageViewer2 it displays OK but not
> with vtkVolume and vtkVolumeRayCastMapper
> Hope you can help.
> Sergio
>
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-- 
Mathieu