This article presents a minimum runnable toy application as a starting point to show how to convert between dicom image and common graphics(i.e. bmp, jpg, tif, etc). The two open source libraries our sample application based on are DCMTK and CxImage.
The DICOM standard(Digital Imaging and Communications in Medicine) is a standard created by the National Electrical Manufacturers Association (NEMA) to ease the distribution and exchange of medical images, such as CT scans, MRIs, and ultrasound. In this article we focus on the file format conversions, the file format is mainly described in Part 10 of the DICOM standard, you can download it here[^]. There is also a brief introduction to the file format available here.
DCMTK is a widely used open source implemenation of the DICOM standard, it is a collection of C/C++ libraries and applications in complete source code. To compile the sample in this article you need to download DCMTK first. If you have trouble building the downloaded DCMTK package, please refer to DCMTK for Dummies.
Another library used in this article is CxImage, it is a C++ class that can load, save, display, transform images in a very simple and fast way. It supports almost all the common graphic types, such as bmp, jpg, tiff, png, etc. In this article we expand this library to support displaying and transforming dicom images by using the dicom format encoding/decoding features provided by DCMTK. Download CxImage and follow its usage guidance to make sure it can be compiled successfully on your machine.
We simply derive our CxImageDCM class from the base calss CxImage. Doing so, the CxImageDCM class can load and decode the common graphics using the methods inheriting from the base class. There are three extra methods in the derived class, LoadDCM(…), SaveAsDCM(…), SaveAsJPG(…), they are used to decode, encode and convert a dicom image, respectively.
//
class CxImageDCM : public CxImage
{
public:
CxImageDCM();
virtual ~CxImageDCM();
bool LoadDCM(const TCHAR* filename);
bool SaveAsDCM(const TCHAR* filename);
bool SaveAsJPG(const TCHAR* fileName);
};//
};//
In the sample application, a dicom image is loaded and decoded with the classes provided by DCMTK, then it is converted to a temporary bitmap file for later manipulations.
//
bool CxImageDCM::LoadDCM(const TCHAR* filename)
{
DcmFileFormat *dfile = new DcmFileFormat();
OFCondition cond = dfile->loadFile(filename, EXS_Unknown,
EGL_withoutGL,DCM_MaxReadLength,OFFalse);
if (cond.bad()) {
AfxMessageBox(cond.text());
}
E_TransferSyntax xfer = dfile->getDataset()->getOriginalXfer();
DicomImage *di = new DicomImage(dfile, xfer,
CIF_AcrNemaCompatibility ,
0, 1);
if (di->getStatus() != EIS_Normal)
AfxMessageBox(DicomImage::getString(di->getStatus()));
di->writeBMP("c:\\from_dicom.bmp",24);
return CxImage::Load("c:\\from_dicom.bmp",CXIMAGE_FORMAT_BMP);
}//
After loading a dcm file, you can save it as a common graphic file through the encoding features provided by CxImage, or you may also use DCMTK’s encoding plugins to do the converting(however, CxImage supports more formats).
//
bool CxImageDCM::SaveAsJPG(const TCHAR* fileName)
{//you may also use DCMTK's JPG encoding plug-in
return CxImage::Save(fileName,CXIMAGE_FORMAT_JPG);
}//
To convert a common graphic file to a dcm file, you need to load the common graphic first, then set the necessary tag and copy the pixel data to the destination dcm file.
//
bool CxImageDCM::SaveAsDCM(const TCHAR* filename)
{
CxImageDCM::IncreaseBpp(24);
char uid[100];
DcmFileFormat fileformat;
DcmDataset *dataset = fileformat.getDataset();
dataset->putAndInsertString(DCM_SOPClassUID,
UID_SecondaryCaptureImageStorage);
/* ... */
// dataset->putAndInsertUint32(DCM_MetaElementGroupLength,128);
dataset->putAndInsertUint16(DCM_FileMetaInformationVersion,
0x0001);
/* ... */
dataset->putAndInsertString(DCM_UID,
UID_MultiframeTrueColorSecondaryCaptureImageStorage);
dataset->putAndInsertString(DCM_PhotometricInterpretation,
"RGB");
//add more tags here
/* ... */
BYTE* pData=new BYTE[GetHeight()*info.dwEffWidth];
BYTE* pSrc=GetBits(head.biHeight-1);
BYTE* pDst=pData;
for(long y=0; y < head.biHeight; y++){
memcpy(pDst,pSrc,info.dwEffWidth);
pSrc-=info.dwEffWidth;
pDst+=info.dwEffWidth;
}
dataset->putAndInsertUint8Array(DCM_PixelData,
pData, GetHeight()*info.dwEffWidth);
delete[] pData;
OFCondition status = fileformat.saveFile(filename,
EXS_LittleEndianImplicit,EET_UndefinedLength,EGL_withoutGL);
if (status.bad())
AfxMessageBox("Error: cannot write DICOM file ");
return true;
}//
}//
In this article, the encoding feature provided by CxImage is used to convert a dicom image to a jpg file(or other formats CxImage supports). Actually, DCMTK already has a full-fledged utility called dcmj2pnm to convert a dicom image to a bmp, png, tiff or jpg image. For other formats that dcmj2pnm doesn’t support, such as gif, png, tga, pcx, wbmp, etc, you may use CxImage’s encoding features to write your own converting functions. One thing I need to clarify is that our sample application is only a toy utility to give a starting point. To write a decent dicom image converter, there are much more dicom related options need to be considered. For more information, you can refer to the implementation of dcmj2pnm(It is included in the DCMTK source code package).
From my experience, CxImage is sure easy to use, it “can load, save, display, transform images in a simple and fast way”. However, I find it’s annoying when you derive a new image encoder/decoder from the base class CxImage, the base class must know all the derived classes to give a polymophic behavior, it’s somewhat astonishing. Fortunatly, in our sample the derived class CxImageDCM only need the encoding/decoding functions it inherits from the base class, so I didn’t bother to touch the source code of CxImage.
• DCMTK forum.
• CxImage on codeproject. touch the source code of CxImage.
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