Yalantis/uCrop · error · CImgIOException

save_medcon_external(): Failed to save file '%s' with extern

Error message

save_medcon_external(): Failed to save file '%s' with external command 'medcon'.

What it means

save_medcon_external() first saves the image in ANALYZE format to a temp file, then runs the external 'medcon' tool to convert it to DICOM. This error is thrown when the 'medcon' system command returns a non-zero exit status, meaning the DICOM conversion failed and the target file was not produced.

Source

Thrown at ucrop/src/main/jni/CImg.h:63843

    **/
    const CImg<T>& save_medcon_external(const char *const filename) const {
      if (!filename)
        throw CImgArgumentException(_cimg_instance
                                    "save_medcon_external(): Specified filename is (null).",
                                    cimg_instance);
      if (is_empty()) { cimg::fempty(0,filename); return *this; }

      CImg<charT> command(1024), filename_tmp(256), body(256);
      do {
        cimg_snprintf(filename_tmp,filename_tmp._width,"%s.hdr",cimg::filenamerand());
      } while (cimg::path_exists(filename_tmp));
      save_analyze(filename_tmp);
      cimg_snprintf(command,command._width,"\"%s\" -w -c dicom -o \"%s\" -f \"%s\"",
                    cimg::medcon_path(),
                    CImg<charT>::string(filename)._system_strescape().data(),
                    CImg<charT>::string(filename_tmp)._system_strescape().data());
      if (cimg::system(command,cimg::medcon_path())!=0)
        throw CImgIOException(_cimg_instance
                                "save_medcon_external(): Failed to save file '%s' with external command 'medcon'.",
                                cimg_instance,
                                filename);
      std::remove(filename_tmp);
      cimg::split_filename(filename_tmp,body);
      cimg_snprintf(filename_tmp,filename_tmp._width,"%s.img",body._data);
      std::remove(filename_tmp);

      if (!cimg::path_exists(filename)) {
        cimg_snprintf(command,command._width,"m000-%s",filename);
        if (!cimg::path_exists(command)) {
          cimg::fclose(cimg::fopen(filename,"r"));
          throw CImgIOException(_cimg_instance
                                "save_medcon_external(): Failed to save file '%s' with external command 'medcon'.",
                                cimg_instance,
                                filename);
        }
      }

View on GitHub (pinned to f788b534b4)

Solutions

Verify medcon is installed and cimg::medcon_path() points to it; run the constructed 'medcon -w -c dicom ...' command manually to see the real error.
Install or upgrade (X)Medcon to a version supporting the image geometry/pixel type.
Check that the temp and output directories are writable.
Convert the image to a supported type/geometry before calling save_medcon_external().
Use an alternative DICOM writing library (e.g. dcmtk) if medcon is unavailable.

Example fix

// before
img.save_medcon_external("slice.dcm");
// after
try { img.save_medcon_external("slice.dcm"); }
catch (CImgIOException& e) { std::fprintf(stderr, "medcon failed: %s", e.what()); img.save_analyze("slice.img"); }

Defensive patterns

Strategy: try-catch

Validate before calling

bool medconAvailable() { return std::system("medcon -v > /dev/null 2>&1") == 0; }
// also ensure image geometry/type are DICOM-compatible before saving

Try / catch

try {
  img.save_medcon_external(dicomFile);
} catch (CImgIOException& e) {
  std::fprintf(stderr, "medcon conversion failed: %s", e.what());
  // fall back to ANALYZE output or another DICOM writer
}

Prevention

Install (X)Medcon on all hosts running the pipeline and check medcon_path().
Match image dimensions/pixel type to what medcon's DICOM encoder accepts.
Keep temp and output directories writable.
Test with the medcon version deployed; output behavior varies between versions.

When it happens

Trigger: Calling save_medcon_external(filename) when: medcon is not installed or cimg::medcon_path() is wrong; the medcon DICOM conversion fails on the generated ANALYZE temp data (unsupported dimensions/pixel type); permissions or disk issues abort the conversion.

Common situations: Medical imaging pipelines deployed on hosts without (X)Medcon installed; medcon version too old for the image geometry; 3D/volumetric or unusual pixel-type images that medcon's dicom converter rejects.

Related errors

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/08eb7dac13e9c811. Report an issue: GitHub.