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

[Bradley Lowekamp]

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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