From: Ian Scott <ian.scott@st...> - 2004-02-04 18:23:05
From: Martin G. Roberts
Sent: Wednesday, February 04, 2004 5:58 PM
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
Or do we need two attributes: one signed, one unsigned and a bool to say
which one is valid?
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