Yalantis/uCrop · error · CImgIOException

load_camera(): This function requires features from the Open

Error message

load_camera(): This function requires features from the OpenCV library ('-Dcimg_use_opencv' must be defined).

What it means

load_camera() is only implemented when CImg is compiled with OpenCV support (cimg_use_opencv defined). Without it, the #else branch throws CImgIOException telling the user the build lacks OpenCV features. The camera code path is entirely absent from the binary.

Source

Thrown at ucrop/src/main/jni/CImg.h:60134

        captures[camera_index]->set(_cimg_cap_prop_frame_height,capture_height);
        captures_h[camera_index] = capture_height;
      }
      for (unsigned int i = 0; i<skip_frames; ++i) captures[camera_index]->grab();
      cv::Mat cvimg;
      captures[camera_index]->read(cvimg);
      if (cvimg.empty()) {
        cimg::mutex(9,0);
        load_camera(camera_index,0,0,0,true); // Release camera
        throw CImgIOException(_cimg_instance
                              "load_camera(): Failed to retrieve a %ux%u frame from camera #%u.",
                              cimg_instance,
                              capture_width,capture_height,camera_index);
      } else _cvmat2cimg(cvimg).move_to(*this);
      cimg::mutex(9,0);
      return *this;
#else
      cimg::unused(camera_index,skip_frames,release_camera,capture_width,capture_height);
      throw CImgIOException(_cimg_instance
                            "load_camera(): This function requires features from the OpenCV library "
                            "('-Dcimg_use_opencv' must be defined).",
                            cimg_instance);
#endif
    }

    //! Load image from a camera stream, using OpenCV \newinstance.
    static CImg<T> get_load_camera(const unsigned int camera_index=0,
                                   const unsigned int capture_width=0, const unsigned int capture_height=0,
                                   const unsigned int skip_frames=0, const bool release_camera=true) {
      return CImg<T>().load_camera(camera_index,capture_width,capture_height,skip_frames,release_camera);
    }

    //! Load image using various non-native ways.
    /**
       \param filename Filename, as a C-string.
    **/
    CImg<T>& load_other(const char *const filename) {

View on GitHub (pinned to f788b534b4)

Solutions

1. Recompile defining cimg_use_opencv and link against OpenCV (add -Dcimg_use_opencv -lopencv_videoio -lopencv_core ...).
2. If OpenCV is not an option, capture frames with a platform API (V4L2, AVFoundation, CameraX) and load the buffers via CImg.
3. Add a runtime/build-time feature check and avoid load_camera() in builds without it.

Example fix

// before
img.load_camera(0); // throws: no OpenCV in build
// after (build config)
// CXXFLAGS: -Dcimg_use_opencv -I/usr/include/opencv4
// LDFLAGS: -lopencv_core -lopencv_videoio
img.load_camera(0);

#ifndef cimg_use_opencv
#error "load_camera() requires -Dcimg_use_opencv and OpenCV linked"
#endif

try { img.load_camera(idx); }
catch (CImgIOException&) { /* use platform camera API or fail fast at startup */ }

When it happens

Trigger: Any call to load_camera() in a build where cimg_use_opencv was not defined at compile time (missing -Dcimg_use_opencv and OpenCV headers/libs in the include/link line).

Common situations: Vendored CImg.h in an Android NDK/JNI build (like ucrop) compiled without OpenCV; third-party prebuilt CImg without the flag; dropping CImg.h into a project and expecting camera support out of the box.

Related errors

• save_video(): Cannot output streamed video, as this requires
• load_magick(): Unable to load file '%s' unless libMagick++ i
• _cimg2cvmat() : Instance image is empty.
• _cimg2cvmat() : Invalid number of channels (should be '1' or
• _cvmat2cimg() : pixel type '%s' is not supported.

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/6b3ac75d26d4feae. Report an issue: GitHub.