Hi
I'm modifying octave-forge/extra/dicom/src/dicominfo.cpp to handle data
which are arrays, i.e. VM>1. I realize that not many people will know DICOM,
let alone GDCM, but I'd appreciate any feedback in any case. (There's some
generic octave questions at the end)
Also, it would be good if someone could test the current dicominfo on
systems with different byteorders. I suspect that it'll only work when the
byteorder of the dicom file is the same as the one of the machine you're
running it on.
I had a look at gdcm example code and it seems to me that we cannot really
use memcpy to get from the dicom raw data to octave data. This presumably
wouldn't work when byteswapping is needed (or other "transfer syntax"). In
any case, I wouldn't know if memcpy would work with arrays (I'm not sure if
it's guaranteed by DICOM that the subsequent members are stored
consecutively, although it's very likely of course). In an attempt to handle
this (and avoid horrible code repetition) I came up with the following
modification for element2value() in dicominfo.cpp:
------------------ current code -------------------
if (vr & gdcm::VR::US) {// unsigned short
uint16_t usval ;
memcpy(&usval, elem->GetByteValue()->GetPointer(), 2);
*ov=usval;
if(chatty) octave_stdout << '[' << usval << "]\n";
} else ...
// almost repeated for lots of VRs and types
return DICOM_OK;
-------------------- new code -----------------
if (vr & gdcm::VR::US) {// unsigned short
return element2intvalueHelper<gdcm::VR::US>(ov, elem, chatty);
} else ...
// repeated for lots of VRs
---------------------- new function definition (in dicominfo.cpp)
---------------------
template <gdcm::VR::VRType vrtype>
int element2intvalueHelper(octave_value *ov, const gdcm::DataElement * elem,
const int chatty) {
if( !elem->IsEmpty() ) {
// find type that corresponds to this VR
typedef typename gdcm::VRToType<vrtype >::Type actual_type;
gdcm::Element<vrtype,gdcm::VM::VM1_n> el;
el.Set( elem->GetValue() );
intNDArray<octave_int<actual_type> > val(dim_vector (el.GetLength(),1));
for (unsigned i=0; i<el.GetLength(); ++i)
val(i) = el.GetValue(i);
*ov=val;
if(chatty) octave_stdout << '[' << val << "]\n";
return DICOM_OK;
}
else
{
return DICOM_NOTHING_ASSIGNED;
}
}
-------------------------------------------------------------------------
This seems to work. It might be somewhat inefficient though, as we're
creating a temporary array, copying to an octave_value, and then getting rid
of it. I'm not sure how to avoid this, or even if it's an issue.
Also, it's annoying that I need to have 2 separate code sets for ints and
floats (as I need intNDArray<octave_int<short> > etc because of missing
constructors in octave_value).
Any suggestions for improvements?
Thanks
Kris Thielemans
Algorithms and Software Consulting Ltd
Honorary Lecturer at Imperial College London
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