From: Martin G. Roberts
Sent: Wednesday, February 04, 2004 5:58 PM
To: 'firstname.lastname@example.org'; 'On'
Cc: Chris Wolstenholme; Ian Scott
Subject: Dicom reader - ambiguity of pixel padding sign
Firstly I did not receive your email regarding this, probably because our internal email servers recently changed our proxy addresses, so I probably need to change the one on SourceForge to domain man.ac.uk (not isbe.man.ac.uk). Apologies therefore in not noticing this.
As regards the actual change, I can only imagine this is due to a change in the pixel_padding type in the dicom header.
I changed this from unsigned short to signed short in order to get the code to compile at all under gcc-Linux. The contradiction was that this is being read using the SS (i.e. signed short) template specialisation in vil_dicom. Gcc objects to the type conflict, though MSVC 6 and 7 appear to accept it. The DICOM dictionary I have unhelpfully defines the PIXELPADDINGVALUE attribute to be either signed or unsigned. I presume the test data requires unsigned, but of course the code might still fail on any file which adopted the other half of the ambiguity.
I will refrain from expressing my personal opinions on a standard which permits such an ambiguity, and will happily change it back to unsigned if the VXL community decide that is the VXL DICOM standard; however I would then change the read to an unsigned specialisation also.
Sorry if I inadvertently caused a test fail, but I view that as at least an improvement on a compilation fail.
Finally I would not be too surprised if the test data file was not strictly conformant anyway. We need to decide how to interpret the ambiguity of the “standard”; not necessarily get the code to read a hand-written 5*3 test file if 90% of real manufacturers have gone for the signed option.
So any requests: Signed or Unsigned for PIXELPADDINGVALUE ?
I will consistently amend to requested majority on Friday and change test if necessary.
Or do we need two attributes: one signed, one unsigned and a bool to say which one is valid?