Yalantis/uCrop · error · CImgArgumentException

save_graphicsmagick_external(): Specified filename is (null)

Error message

save_graphicsmagick_external(): Specified filename is (null).

What it means

save_graphicsmagick_external() converts/saves the image by invoking the external gm (GraphicsMagick) binary, so a non-null filename is mandatory. It throws CImgArgumentException when the filename is null. gm must be installed for the conversion to succeed.

Source

Thrown at ucrop/src/main/jni/CImg.h:63713

                              "save_gzip_external(): Failed to save file '%s' with external command 'gzip'.",
                              cimg_instance,
                              filename);

      std::remove(filename_tmp);
      return *this;
    }

    //! Save image using GraphicsMagick's external binary.
    /**
       \param filename Filename, as a C-string.
       \param quality Image quality (expressed in percent), when the file format supports it.
       \note This method uses \c gm, an external executable binary provided by
         <a href="http://www.graphicsmagick.org">GraphicsMagick</a>.
       It must be installed for the method to succeed.
    **/
    const CImg<T>& save_graphicsmagick_external(const char *const filename, const unsigned int quality=100) const {
      if (!filename)
        throw CImgArgumentException(_cimg_instance
                                    "save_graphicsmagick_external(): Specified filename is (null).",
                                    cimg_instance);
      if (is_empty()) { cimg::fempty(0,filename); return *this; }
      if (_depth>1)
        cimg::warn(_cimg_instance
                   "save_other(): File '%s', saving a volumetric image with an external call to "
                   "GraphicsMagick only writes the first image slice.",
                   cimg_instance,filename);

#ifdef cimg_use_png
#define _cimg_sge_extension1 "png"
#define _cimg_sge_extension2 "png"
#else
#define _cimg_sge_extension1 "pgm"
#define _cimg_sge_extension2 "ppm"
#endif
      CImg<charT> command(1024), filename_tmp(256);
      do {

View on GitHub (pinned to f788b534b4)

Solutions

1. Pass a valid filename: img.save_graphicsmagick_external("out.jpg", 90).
2. Default the filename when null before calling.
3. Prefer CImg's built-in save formats (which dispatch internally) if GraphicsMagick isn't available.

Example fix

// before
img.save_graphicsmagick_external(NULL);
// after
img.save_graphicsmagick_external("output.png", 100);

if (!fname || !*fname) fname = "output.png";
img.save_graphicsmagick_external(fname, /*quality*/90);

bool validPath(const char *p) { return p != nullptr && p[0] != '\0'; }

try { img.save_graphicsmagick_external(path.c_str()); }
catch (cimg_library::CImgArgumentException &e) { std::fprintf(stderr, "gm save: %s\n", e.what()); }
catch (cimg_library::CImgIOException &e) { std::fprintf(stderr, "graphicsmagick failed (installed?): %s\n", e.what()); }

When it happens

Trigger: Calling save_graphicsmagick_external() with a null/default filename, or passing a char* that was never initialized.

Common situations: Path built from missing configuration; forgetting the argument since quality has a default value; calling this format on systems where no gm binary exists (the null check fires first).

Related errors

• load_graphicsmagick_external(): Failed to load file '%s' wit
• save_pandore(): Specified filename is (null).
• save_raw(): Specified filename is (null).
• save_ffmpeg_external(): Specified filename is (null).
• save_gzip_external(): Specified filename is (null).

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/96f2ff5734ce9e99. Report an issue: GitHub.