V4l default image size #25500
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V4l default image size #25500
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…ith environment variables before opening VideoCapture Added ability to set default image width and height for V4L capture. This is required for cameras that does not support 640x480 resolution because otherwise V4L capture cannot be opened and failed with "Pixel format of incoming image is unsupported by OpenCV" and then with "can't open camera by index" message. Because of the videoio architecture it is not possible to insert actions between CvCaptureCAM_V4L::CvCaptureCAM_V4L and CvCaptureCAM_V4L::open so the only way I found is to use environment variables to preselect the resolution.
| width = DEFAULT_V4L_WIDTH; | ||
| height = DEFAULT_V4L_HEIGHT; | ||
| width = utils::getConfigurationParameterSizeT("OPENCV_VIDEOIO_V4L_DEFAULT_WIDTH", DEFAULT_V4L_WIDTH); | ||
| height = utils::getConfigurationParameterSizeT("OPENCV_VIDEOIO_V4L_DEFAULT_HEIGHT", DEFAULT_V4L_HEIGHT); |
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What is about const VideoCaptureParameters& params approach?
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Unfortunately it won't work. The VideoCaptureParameters parameter is applied only after the fn_createCaptureCamera_ call. Here is the sequence:
- The
createCaptureis called with theVideoCaptureParameters - The
createCapturecalls the configuredfn_createCaptureCamera_function of the capture backend (which iscreate_V4L_capture_cam in this case) and after the call is succeeded sets the VideoCaptureParameters.
The problem is this is thecreate_V4L_capture_camwhich is failed (inside theCvCaptureCAM_V4L::initCapturefunction) so we have no chance to apply the VideoCaptureParameters. At least without major refactoring of entire factory code.
Note that the utils::getConfigurationParameter... approach is already used here for the normalizePropRange property so the change will not introduce new approaches.
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Added ability to set default image width and height for V4L capture. This is required for cameras that does not support 640x480 resolution because otherwise V4L capture cannot be opened and failed with "Pixel format of incoming image is unsupported by OpenCV" and then with "can't open camera by index" message. Because of the videoio architecture it is not possible to insert actions between CvCaptureCAM_V4L::CvCaptureCAM_V4L and CvCaptureCAM_V4L::open so the only way I found is to use environment variables to preselect the resolution.
Related bug report is #25499
Maybe (but not confirmed) this is also related to #24551
This fix was made and verified in my local environment: capture board AVMATRIX VC42, Ubuntu 20, NVidia Jetson Orin.
Pull Request Readiness Checklist
See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request
Patch to opencv_extra has the same branch name.