[Insight-users] Error reading images with negative values

[Kajetan Berlinger]

Hi Xin,

On Monday 14 August 2006 08:05, Xin Guan wrote:
> Hi,
>
> I'm using ITK image IO to read images. MRI images are okay, but CT images
> -- no matter it's DICOM or converted Analyze files -- always gave some
> weird images. The actual pixel value range is  -16330 to 3000, but the
> loaded image has a range of 0 to 4094.

A range from -16330 to 3000 ist not possible, as the intensity value of a CT 
voxel  is represented by 12 bit. That is from 0 to 4095 or with respect to 
the HU scale -1023 to 3072. 
How do you come to this -16330 to 3000 value range?
Is there perhaps a pixel padding value defined? 
This value is stored in DicomTag (0028,0120). 
If the image is non-rectangular, this value marks pixels used to pad to  
rectangular format.

> It seems that part of the negative 
> values were simply negated to positive. The error remains the same
> regardless of the pixel type specified -- signed short or float.
>
> I followed ITK example DicomSeriesReadSeriesWrite and Image2 (
> itk::ImageFileReader).
>
> I'd appreciate any help on this. Thanks in advance.
>
> - xin

cu
kaj