{"record":{"id":"1ee524b600126b6c","repo":"Yalantis/uCrop","slug":"load-camera-failed-to-retrieve-a-ux-u-frame-fr","errorCode":null,"errorMessage":"load_camera(): Failed to retrieve a %ux%u frame from camera #%u.","messagePattern":"load_camera\\(\\): Failed to retrieve a %ux%u frame from camera #%u\\.","errorType":"exception","errorClass":"CImgIOException","httpStatus":null,"severity":"error","filePath":"ucrop/src/main/jni/CImg.h","lineNumber":60125,"sourceCode":"        }\n        cimg::mutex(9,0);\n      }\n      cimg::mutex(9);\n      if (capture_width!=captures_w[camera_index]) {\n        captures[camera_index]->set(_cimg_cap_prop_frame_width,capture_width);\n        captures_w[camera_index] = capture_width;\n      }\n      if (capture_height!=captures_h[camera_index]) {\n        captures[camera_index]->set(_cimg_cap_prop_frame_height,capture_height);\n        captures_h[camera_index] = capture_height;\n      }\n      for (unsigned int i = 0; i<skip_frames; ++i) captures[camera_index]->grab();\n      cv::Mat cvimg;\n      captures[camera_index]->read(cvimg);\n      if (cvimg.empty()) {\n        cimg::mutex(9,0);\n        load_camera(camera_index,0,0,0,true); // Release camera\n        throw CImgIOException(_cimg_instance\n                              \"load_camera(): Failed to retrieve a %ux%u frame from camera #%u.\",\n                              cimg_instance,\n                              capture_width,capture_height,camera_index);\n      } else _cvmat2cimg(cvimg).move_to(*this);\n      cimg::mutex(9,0);\n      return *this;\n#else\n      cimg::unused(camera_index,skip_frames,release_camera,capture_width,capture_height);\n      throw CImgIOException(_cimg_instance\n                            \"load_camera(): This function requires features from the OpenCV library \"\n                            \"('-Dcimg_use_opencv' must be defined).\",\n                            cimg_instance);\n#endif\n    }\n\n    //! Load image from a camera stream, using OpenCV \\newinstance.\n    static CImg<T> get_load_camera(const unsigned int camera_index=0,\n                                   const unsigned int capture_width=0, const unsigned int capture_height=0,","sourceCodeStart":60107,"sourceCodeEnd":60143,"githubUrl":"https://github.com/Yalantis/uCrop/blob/f788b534b48c144edf786c8cddbf0e029e637804/ucrop/src/main/jni/CImg.h#L60107-L60143","documentation":"CImg opens the camera and reads a frame with captures[camera_index]->read(cvimg); if the resulting cv::Mat is empty, no frame could be retrieved at the requested resolution, the camera is released and CImgIOException is thrown.","triggerScenarios":"load_camera() with capture_width/capture_height the device cannot deliver and the backend returns an empty Mat; device disconnected/errored after successful open; first grab returned nothing (driver still warming up).","commonSituations":"Requesting unsupported resolutions (e.g. 4K on a 720p webcam with a strict backend); USB bandwidth exhausted with multiple cameras; camera unplugged mid-session; broken driver returning empty frames intermittently.","solutions":["Pass capture_width=0 and capture_height=0 to let the camera use its default resolution instead of forcing an unsupported one.","Retry the capture — transient failures are common right after opening; add a few attempts with small sleeps.","Verify the device is still connected and stable (cables, USB power management).","Lower the requested resolution or use fewer simultaneous cameras to free USB bandwidth."],"exampleFix":"// before: forces a possibly unsupported resolution\nimg.load_camera(0, 3840, 2160);\n// after\nimg.load_camera(0, 0, 0); // camera default\n// or retry a few times\nfor (int i = 0; i < 5 && img.is_empty(); ++i) { cimg::sleep(100); img.load_camera(0,0,0,false); }","handlingStrategy":"retry","validationCode":"// verify the device can deliver the requested format before forcing resolution\n// prefer load_camera(idx) (0,0 defaults) unless the resolution is known-supported","typeGuard":null,"tryCatchPattern":"for (int attempt = 0; attempt < 5; ++attempt) {\n  try { img.load_camera(idx, w, h); break; }\n  catch (CImgIOException&) { cimg::sleep(200); }\n}","preventionTips":["Use default resolution (0,0) unless the device is known to support the size","Add retry/backoff around frame grabs — first frames often fail","Monitor device hotplug; re-open after disconnect","Limit simultaneous cameras to avoid USB bandwidth exhaustion"],"tags":["cimg","opencv","camera","frame-capture"],"backgroundTag":"empty-result-set","analyzedSha":"f788b534b48c144edf786c8cddbf0e029e637804","analyzedAt":"2026-09-08T08:36:04.887Z","contentChangedAt":"2026-09-08T08:36:04.887Z","schemaVersion":2},"datasetVersion":"2026-09-17T15:17:12.973Z"}