[Insight-users] Image Intensities Changed During DICOM Read-Write-Read in ITK 3.20 vs. ITK 4.4.1

[Bill Lorensen]

DICOM data is often signed after the slope/intercept in applied. Try
setting the type to short rather than unsigned short.


On Mon, Aug 12, 2013 at 9:48 AM, Bradley Lowekamp <blowekamp at mail.nih.gov>wrote:

>
> Do you have the code to share so that it can be easily reproduced?
>
>
> Thanks,
> Brad
>
> On Aug 12, 2013, at 9:33 AM, Constantine Zakkaroff <mnkz at leeds.ac.uk>
> wrote:
>
> > Hello ALL,
> >
> > I'm wondering if anyone can explain what's going on with the changing
> image intensities in a read-write-read round-trip. I think it's a bug, but
> the issues.itk.org is unresponsive at the moment. Another bug? ;)
> >
> > Anyhow, the strange thing is that the results for the round trip
> read-write-read test are very different for ITK 3.20 and ITK 4.4.1.
> >
> > I use to StatisticsImageFilter to examine the intensity values. Here's
> what happens, when I simply read a DICOM image, print stats, save the image
> and read it again, followed by printing the stats:
> >
> > ITK Version: 3.20
> > Stats for original file:
> > Min: 0, Max: 2474, Mean: 169.236, Sigma: 256.719, Variance: 65904.7,
> Sum: 1.40371e+007
> > Stats for saved file:
> > Min: 0, Max: 2471, Mean: 167.132, Sigma: 256.125, Variance: 65600.1,
> Sum: 1.38626e+007
> >
> > ITK Version: 4.4
> > Stats for original file:
> > Min: 0, Max: 2474, Mean: 169.236, Sigma: 256.719, Variance: 65904.7,
> Sum: 1.40371e+007
> > Stats for saved file:
> > Min: 0, Max: 7446, Mean: 509.114, Sigma: 772.59, Variance: 596895, Sum:
> 4.22279e+007
> >
> > In both cases the code is identical. Just compiled against different
> versions of ITK. The images are read and written as itk::Image<unsigned
> short, 3>, with no processing, no changes to any aspect of the images.
> >
> > So, ITK 3.20 introduces a small change, which I'm pretty sure shouldn't
> be there. But in ITK 4.4.1 the scale of intensities changes three-fold.
> >
> > I'd not be surprised by a change of this magnitude if I was photocopying
> those images, but not when using digital software and hardware. :^) Is
> there something I'm not understanding here?
> >
> > None of this happens with read(DICOM)-write(MHD)-read(MHD), where the
> original and round-trip values are identical:
> > Stats for saved file: file0.mhd
> > Min: 0, Max: 2474, Mean: 169.236, Sigma: 256.719, Variance: 65904.7,
> Sum: 1.40371e+007
> >
> > Many thanks,
> > Constantine
> >
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