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

[Constantine Zakkaroff]

Thanks for your reply, Bill. I've tried setting the type to short, and 
it didn't seem to change anything.

Many thanks,
Constantine

On 12/08/2013 15:18, Bill Lorensen wrote:
> 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 <mailto: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
>     <mailto: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 <http://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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