[Dcmlib] Pixel Representation =1

[zhou13 at netscape.net]

  Dear Jean:
 
 I find this in gdcmFile.cxx.
 
 /**
 * \brief Check whether the pixels are signed (1) or UNsigned (0) data.
 * \warning The method defaults to false (UNsigned) when tag 0028|0103
 * is missing.
 * The responsability of checking this value is left to the caller
 * (NO transformation is performed on the pixels to make then >0)
 * @return True when signed, false when UNsigned
 */
 bool File::IsSignedPixelData()
 {
 std::string strSign = GetEntryValue( 0x0028, 0x0103 );
 if ( strSign == GDCM_UNFOUND )
 {
 gdcmWarningMacro( "Pixel Representation (0028,0103) supposed to be "
 << "mandatory");
 return false;
 }
 int sign = atoi( strSign.c_str() );
 if ( sign == 0 ) 
 {
 return false;
 }
 return true;
 }
    So, using GDCM doesn't guarantee that the signess of pixel will be handled correctly. People must actively call this method and custom transform the value. A better way would be hiding these details in side the reader and people would always get the correct value regardless of the Pixel Representation settings.
 
 Regards,
 Li Zhou
 
 
 -----Original Message-----
 From: jpr at creatis.insa-lyon.fr
 To: zhou13 at netscape.net
 Cc: dcmlib at creatis.insa-lyon.fr
 Sent: Mon, 13 Nov 2006 9:21 PM
 Subject: Re: [Dcmlib] Pixel Representation =1
 
  zhou13 at netscape.net wrote: 
 
 > Hello list, 
 > 
 > Does GDCM correctly handle the Pixel Representation tag? When the > Pixel Representation value is 1, the stored value in DICOM is two's > complement ( 16 bit signed short ). I have been using VTK's DICOM > reader but it can't handle this situation. 
 
 I didn't know VTK's DICOM reader had this kind of trouble. 
 GDCM deals correctly with pixel representation. 
 GDCM comes with a vtkGdcmReader() , with the same API than vtk's DICOM Reader. 
 
 > So i am investigating ITK's DICOM reader which is based on GDCM. I > have some studies from a GE ProSpeed CT which actually set the Pixel > Representation tag to 1. 
 
 If you download gdcm, just use vtkgdcmViewer2 yourDicomFileName 
 to be sure it works. 
 You can have a look at the dicom header using : 
 PrintFile filein=yourDicomFileName 
 
 HTH 
 
 Jean-Pierre Roux 
 from gdcm team. 
 
 > 
 > Thanks. 
 > Li Zhou 
 > 
 > 
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