OpenCV Types

This page documents OpenCV types that could not be automatically included in the documentation.

Aruco Detector Parameters

class cv2.aruco_DetectorParameters
__init__()

Initialize self. See help(type(self)) for accurate signature.

adaptiveThreshConstant
adaptiveThreshWinSizeMax
adaptiveThreshWinSizeMin
adaptiveThreshWinSizeStep
aprilTagCriticalRad
aprilTagDeglitch
aprilTagMaxLineFitMse
aprilTagMaxNmaxima
aprilTagMinClusterPixels
aprilTagMinWhiteBlackDiff
aprilTagQuadDecimate
aprilTagQuadSigma
cornerRefinementMaxIterations
cornerRefinementMethod
cornerRefinementMinAccuracy
cornerRefinementWinSize
static create() → retval

.

errorCorrectionRate
markerBorderBits
maxErroneousBitsInBorderRate
maxMarkerPerimeterRate
minCornerDistanceRate
minDistanceToBorder
minMarkerDistanceRate
minMarkerPerimeterRate
minOtsuStdDev
perspectiveRemoveIgnoredMarginPerCell
perspectiveRemovePixelPerCell
polygonalApproxAccuracyRate

VideoCapture

class cv2.VideoCapture
__init__()

Initialize self. See help(type(self)) for accurate signature.

get(propId) → retval

. @brief Returns the specified VideoCapture property . . @param propId Property identifier from cv::VideoCaptureProperties (eg. cv::CAP_PROP_POS_MSEC, cv::CAP_PROP_POS_FRAMES, …) . or one from @ref videoio_flags_others . @return Value for the specified property. Value 0 is returned when querying a property that is . not supported by the backend used by the VideoCapture instance. . . @note Reading / writing properties involves many layers. Some unexpected result might happens . along this chain. . @code {.txt} . VideoCapture -> API Backend -> Operating System -> Device Driver -> Device Hardware . @endcode . The returned value might be different from what really used by the device or it could be encoded . using device dependent rules (eg. steps or percentage). Effective behaviour depends from device . driver and API Backend

getBackendName() → retval

. @brief Returns used backend API name . . @note Stream should be opened.

grab() → retval

. @brief Grabs the next frame from video file or capturing device. . . @return true (non-zero) in the case of success. . . The method/function grabs the next frame from video file or camera and returns true (non-zero) in . the case of success. . . The primary use of the function is in multi-camera environments, especially when the cameras do not . have hardware synchronization. That is, you call VideoCapture::grab() for each camera and after that . call the slower method VideoCapture::retrieve() to decode and get frame from each camera. This way . the overhead on demosaicing or motion jpeg decompression etc. is eliminated and the retrieved frames . from different cameras will be closer in time. . . Also, when a connected camera is multi-head (for example, a stereo camera or a Kinect device), the . correct way of retrieving data from it is to call VideoCapture::grab() first and then call . VideoCapture::retrieve() one or more times with different values of the channel parameter. . . @ref tutorial_kinect_openni

isOpened() → retval

. @brief Returns true if video capturing has been initialized already. . . If the previous call to VideoCapture constructor or VideoCapture::open() succeeded, the method returns . true.

open(filename[, apiPreference]) → retval

. @brief Opens a video file or a capturing device or an IP video stream for video capturing. . . @overload . . Parameters are same as the constructor VideoCapture(const String& filename, int apiPreference = CAP_ANY) . @return true if the file has been successfully opened . . The method first calls VideoCapture::release to close the already opened file or camera.

open(index[, apiPreference]) -> retval . @brief Opens a camera for video capturing . . @overload . . Parameters are same as the constructor VideoCapture(int index, int apiPreference = CAP_ANY) . @return true if the camera has been successfully opened. . . The method first calls VideoCapture::release to close the already opened file or camera.

read([image]) → retval, image

. @brief Grabs, decodes and returns the next video frame. . . @param [out] image the video frame is returned here. If no frames has been grabbed the image will be empty. . @return false if no frames has been grabbed . . The method/function combines VideoCapture::grab() and VideoCapture::retrieve() in one call. This is the . most convenient method for reading video files or capturing data from decode and returns the just . grabbed frame. If no frames has been grabbed (camera has been disconnected, or there are no more . frames in video file), the method returns false and the function returns empty image (with %cv::Mat, test it with Mat::empty()). . . @note In @ref videoio_c “C API”, functions cvRetrieveFrame() and cv.RetrieveFrame() return image stored inside the video . capturing structure. It is not allowed to modify or release the image! You can copy the frame using . cvCloneImage and then do whatever you want with the copy.

release() → None

. @brief Closes video file or capturing device. . . The method is automatically called by subsequent VideoCapture::open and by VideoCapture . destructor. . . The C function also deallocates memory and clears *capture pointer.

retrieve([image[, flag]]) → retval, image

. @brief Decodes and returns the grabbed video frame. . . @param [out] image the video frame is returned here. If no frames has been grabbed the image will be empty. . @param flag it could be a frame index or a driver specific flag . @return false if no frames has been grabbed . . The method decodes and returns the just grabbed frame. If no frames has been grabbed . (camera has been disconnected, or there are no more frames in video file), the method returns false . and the function returns an empty image (with %cv::Mat, test it with Mat::empty()). . . @sa read() . . @note In @ref videoio_c “C API”, functions cvRetrieveFrame() and cv.RetrieveFrame() return image stored inside the video . capturing structure. It is not allowed to modify or release the image! You can copy the frame using . cvCloneImage and then do whatever you want with the copy.

set(propId, value) → retval

. @brief Sets a property in the VideoCapture. . . @param propId Property identifier from cv::VideoCaptureProperties (eg. cv::CAP_PROP_POS_MSEC, cv::CAP_PROP_POS_FRAMES, …) . or one from @ref videoio_flags_others . @param value Value of the property. . @return true if the property is supported by backend used by the VideoCapture instance. . @note Even if it returns true this doesn’t ensure that the property . value has been accepted by the capture device. See note in VideoCapture::get()