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The title says it all. What is the difference between dcm2pnm (http://support.dcmtk.org/docs/dcm2pnm.html), dcmj2pnm (http://support.dcmtk.org/docs/dcmj2pnm.html) and dcml2pnm (http://support.dcmtk.org/docs/dcml2pnm.html) commands of dcmtk toolkit (http://support.dcmtk.org/docs/pages.html)? They all seem to convert dicom images to other formats. Are there any special situations where one should be preferred over others?

Edit: It seems dcml2pnm supports more formats. Why not use that for all purposes? What are the advantages of other commands?

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I am the DCMTK developer.

The difference between the three DCMTK command line tools is: support for compressed DICOM images and output formats.

  • dcm2pnm was the original tool that has been developed more than 20 years ago and which originally only supported the image format PNM/PGM for output (that's also why the tool is called "dcm2pnm" and not "dcm2img" or the like). And, because at that time the DCMTK did not support any encapsulated transfer syntaxes (i.e. compression), only uncompressed DICOM images can be read.
  • dcmj2pnm is located in DCMTK's submodule "dcmjpeg" and adds support for JPEG-compressed DICOM images (based on the IJG library) as well as the JPEG image format for output.
  • dcml2pnm is located in DCMTK's submodule "dcmjpls" and adds support for JPEG-LS-compressed DICOM images (based on the CharLS library). It does not support conventional JPEG.

All this is probably more obvious from the source code package than from the binary package but it is also mentioned in the above referenced documentation (see "Description" section).

If you'd ask why there are three different tools (in fact, there is also a fourth one for JPEG-2000 support but that not part of the public DCMTK), my answer would be: this is mainly for historical reasons but also for reason of keeping dependencies between the various DCMTK modules as simple as possible. Furthermore, we consider the command line tools as a kind of sample applications of the underlying C++ class library. So, if you'd need a tool that supports all image compression schemes available in the DCMTK, it should be easy to write such a tool.

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  • Very well explained. Do these functions return true/false or 1/0 etc to indicate whether the dicom file could be opened and converted properly?
    – rnso
    Commented Apr 12, 2017 at 12:12
  • @rnso Yes, they return these exit codes. There are also plans to use different exit codes for different types of errors and to document them in the man page but this is still on our to-do list (for all DCMTK command line tools, of course).
    – J. Riesmeier
    Commented Apr 12, 2017 at 13:50
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dcmj2pnm adds JPEG codecs to the dcm2pnm functionality. Thus, it is capable of handling JPEG compressed DICOM data and produce JPEG output images. So it is a superset of dcm2pnm's functionality. I think this is, because dcmtk offers different compile options which allow to include / exclude libjpeg. Just reflects the toolkit's options to the accompanying command line tools. Confirmed by the list of file formats when you start with option -h

For dcml2pnm I am not sure, but this is a good guess: Same as for JPEG but includes the JPEG-LS encoder which is another optional 3rd party toolkit for dcmtk.

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