Object Detection ================ .. highlight:: cpp gpu::HOGDescriptor ------------------ .. ocv:struct:: gpu::HOGDescriptor The class implements Histogram of Oriented Gradients ([Dalal2005]_) object detector. :: struct CV_EXPORTS HOGDescriptor { enum { DEFAULT_WIN_SIGMA = -1 }; enum { DEFAULT_NLEVELS = 64 }; enum { DESCR_FORMAT_ROW_BY_ROW, DESCR_FORMAT_COL_BY_COL }; HOGDescriptor(Size win_size=Size(64, 128), Size block_size=Size(16, 16), Size block_stride=Size(8, 8), Size cell_size=Size(8, 8), int nbins=9, double win_sigma=DEFAULT_WIN_SIGMA, double threshold_L2hys=0.2, bool gamma_correction=true, int nlevels=DEFAULT_NLEVELS); size_t getDescriptorSize() const; size_t getBlockHistogramSize() const; void setSVMDetector(const vector& detector); static vector getDefaultPeopleDetector(); static vector getPeopleDetector48x96(); static vector getPeopleDetector64x128(); void detect(const GpuMat& img, vector& found_locations, double hit_threshold=0, Size win_stride=Size(), Size padding=Size()); void detectMultiScale(const GpuMat& img, vector& found_locations, double hit_threshold=0, Size win_stride=Size(), Size padding=Size(), double scale0=1.05, int group_threshold=2); void getDescriptors(const GpuMat& img, Size win_stride, GpuMat& descriptors, int descr_format=DESCR_FORMAT_COL_BY_COL); Size win_size; Size block_size; Size block_stride; Size cell_size; int nbins; double win_sigma; double threshold_L2hys; bool gamma_correction; int nlevels; private: // Hidden } Interfaces of all methods are kept similar to the ``CPU HOG`` descriptor and detector analogues as much as possible. .. Sample code:: * : An example applying the HOG descriptor for people detection can be found at opencv_source_code/samples/cpp/peopledetect.cpp * : A GPU example applying the HOG descriptor for people detection can be found at opencv_source_code/samples/gpu/hog.cpp * : PYTHON : An example applying the HOG descriptor for people detection can be found at opencv_source_code/samples/python2/peopledetect.py gpu::HOGDescriptor::HOGDescriptor ------------------------------------- Creates the ``HOG`` descriptor and detector. .. ocv:function:: gpu::HOGDescriptor::HOGDescriptor(Size win_size=Size(64, 128), Size block_size=Size(16, 16), Size block_stride=Size(8, 8), Size cell_size=Size(8, 8), int nbins=9, double win_sigma=DEFAULT_WIN_SIGMA, double threshold_L2hys=0.2, bool gamma_correction=true, int nlevels=DEFAULT_NLEVELS) :param win_size: Detection window size. Align to block size and block stride. :param block_size: Block size in pixels. Align to cell size. Only (16,16) is supported for now. :param block_stride: Block stride. It must be a multiple of cell size. :param cell_size: Cell size. Only (8, 8) is supported for now. :param nbins: Number of bins. Only 9 bins per cell are supported for now. :param win_sigma: Gaussian smoothing window parameter. :param threshold_L2hys: L2-Hys normalization method shrinkage. :param gamma_correction: Flag to specify whether the gamma correction preprocessing is required or not. :param nlevels: Maximum number of detection window increases. gpu::HOGDescriptor::getDescriptorSize ----------------------------------------- Returns the number of coefficients required for the classification. .. ocv:function:: size_t gpu::HOGDescriptor::getDescriptorSize() const gpu::HOGDescriptor::getBlockHistogramSize --------------------------------------------- Returns the block histogram size. .. ocv:function:: size_t gpu::HOGDescriptor::getBlockHistogramSize() const gpu::HOGDescriptor::setSVMDetector -------------------------------------- Sets coefficients for the linear SVM classifier. .. ocv:function:: void gpu::HOGDescriptor::setSVMDetector(const vector& detector) gpu::HOGDescriptor::getDefaultPeopleDetector ------------------------------------------------ Returns coefficients of the classifier trained for people detection (for default window size). .. ocv:function:: static vector gpu::HOGDescriptor::getDefaultPeopleDetector() gpu::HOGDescriptor::getPeopleDetector48x96 ---------------------------------------------- Returns coefficients of the classifier trained for people detection (for 48x96 windows). .. ocv:function:: static vector gpu::HOGDescriptor::getPeopleDetector48x96() gpu::HOGDescriptor::getPeopleDetector64x128 ----------------------------------------------- Returns coefficients of the classifier trained for people detection (for 64x128 windows). .. ocv:function:: static vector gpu::HOGDescriptor::getPeopleDetector64x128() gpu::HOGDescriptor::detect ------------------------------ Performs object detection without a multi-scale window. .. ocv:function:: void gpu::HOGDescriptor::detect(const GpuMat& img, vector& found_locations, double hit_threshold=0, Size win_stride=Size(), Size padding=Size()) :param img: Source image. ``CV_8UC1`` and ``CV_8UC4`` types are supported for now. :param found_locations: Left-top corner points of detected objects boundaries. :param hit_threshold: Threshold for the distance between features and SVM classifying plane. Usually it is 0 and should be specfied in the detector coefficients (as the last free coefficient). But if the free coefficient is omitted (which is allowed), you can specify it manually here. :param win_stride: Window stride. It must be a multiple of block stride. :param padding: Mock parameter to keep the CPU interface compatibility. It must be (0,0). gpu::HOGDescriptor::detectMultiScale ---------------------------------------- Performs object detection with a multi-scale window. .. ocv:function:: void gpu::HOGDescriptor::detectMultiScale(const GpuMat& img, vector& found_locations, double hit_threshold=0, Size win_stride=Size(), Size padding=Size(), double scale0=1.05, int group_threshold=2) :param img: Source image. See :ocv:func:`gpu::HOGDescriptor::detect` for type limitations. :param found_locations: Detected objects boundaries. :param hit_threshold: Threshold for the distance between features and SVM classifying plane. See :ocv:func:`gpu::HOGDescriptor::detect` for details. :param win_stride: Window stride. It must be a multiple of block stride. :param padding: Mock parameter to keep the CPU interface compatibility. It must be (0,0). :param scale0: Coefficient of the detection window increase. :param group_threshold: Coefficient to regulate the similarity threshold. When detected, some objects can be covered by many rectangles. 0 means not to perform grouping. See :ocv:func:`groupRectangles` . gpu::HOGDescriptor::getDescriptors -------------------------------------- Returns block descriptors computed for the whole image. .. ocv:function:: void gpu::HOGDescriptor::getDescriptors(const GpuMat& img, Size win_stride, GpuMat& descriptors, int descr_format=DESCR_FORMAT_COL_BY_COL) :param img: Source image. See :ocv:func:`gpu::HOGDescriptor::detect` for type limitations. :param win_stride: Window stride. It must be a multiple of block stride. :param descriptors: 2D array of descriptors. :param descr_format: Descriptor storage format: * **DESCR_FORMAT_ROW_BY_ROW** - Row-major order. * **DESCR_FORMAT_COL_BY_COL** - Column-major order. The function is mainly used to learn the classifier. gpu::CascadeClassifier_GPU -------------------------- .. ocv:class:: gpu::CascadeClassifier_GPU Cascade classifier class used for object detection. Supports HAAR and LBP cascades. :: class CV_EXPORTS CascadeClassifier_GPU { public: CascadeClassifier_GPU(); CascadeClassifier_GPU(const string& filename); ~CascadeClassifier_GPU(); bool empty() const; bool load(const string& filename); void release(); /* Returns number of detected objects */ int detectMultiScale( const GpuMat& image, GpuMat& objectsBuf, double scaleFactor=1.2, int minNeighbors=4, Size minSize=Size()); int detectMultiScale( const GpuMat& image, GpuMat& objectsBuf, Size maxObjectSize, Size minSize = Size(), double scaleFactor = 1.1, int minNeighbors = 4); /* Finds only the largest object. Special mode if training is required.*/ bool findLargestObject; /* Draws rectangles in input image */ bool visualizeInPlace; Size getClassifierSize() const; }; .. Sample code:: * : A cascade classifier example can be found at opencv_source_code/samples/gpu/cascadeclassifier.cpp * : A Nvidea API specific cascade classifier example can be found at opencv_source_code/samples/gpu/cascadeclassifier_nvidia_api.cpp gpu::CascadeClassifier_GPU::CascadeClassifier_GPU ----------------------------------------------------- Loads the classifier from a file. Cascade type is detected automatically by constructor parameter. .. ocv:function:: gpu::CascadeClassifier_GPU::CascadeClassifier_GPU(const string& filename) :param filename: Name of the file from which the classifier is loaded. Only the old ``haar`` classifier (trained by the ``haar`` training application) and NVIDIA's ``nvbin`` are supported for HAAR and only new type of OpenCV XML cascade supported for LBP. gpu::CascadeClassifier_GPU::empty ------------------------------------- Checks whether the classifier is loaded or not. .. ocv:function:: bool gpu::CascadeClassifier_GPU::empty() const gpu::CascadeClassifier_GPU::load ------------------------------------ Loads the classifier from a file. The previous content is destroyed. .. ocv:function:: bool gpu::CascadeClassifier_GPU::load(const string& filename) :param filename: Name of the file from which the classifier is loaded. Only the old ``haar`` classifier (trained by the ``haar`` training application) and NVIDIA's ``nvbin`` are supported for HAAR and only new type of OpenCV XML cascade supported for LBP. gpu::CascadeClassifier_GPU::release --------------------------------------- Destroys the loaded classifier. .. ocv:function:: void gpu::CascadeClassifier_GPU::release() gpu::CascadeClassifier_GPU::detectMultiScale ------------------------------------------------ Detects objects of different sizes in the input image. .. ocv:function:: int gpu::CascadeClassifier_GPU::detectMultiScale(const GpuMat& image, GpuMat& objectsBuf, double scaleFactor=1.2, int minNeighbors=4, Size minSize=Size()) .. ocv:function:: int gpu::CascadeClassifier_GPU::detectMultiScale(const GpuMat& image, GpuMat& objectsBuf, Size maxObjectSize, Size minSize = Size(), double scaleFactor = 1.1, int minNeighbors = 4) :param image: Matrix of type ``CV_8U`` containing an image where objects should be detected. :param objectsBuf: Buffer to store detected objects (rectangles). If it is empty, it is allocated with the default size. If not empty, the function searches not more than N objects, where ``N = sizeof(objectsBufer's data)/sizeof(cv::Rect)``. :param maxObjectSize: Maximum possible object size. Objects larger than that are ignored. Used for second signature and supported only for LBP cascades. :param scaleFactor: Parameter specifying how much the image size is reduced at each image scale. :param minNeighbors: Parameter specifying how many neighbors each candidate rectangle should have to retain it. :param minSize: Minimum possible object size. Objects smaller than that are ignored. The detected objects are returned as a list of rectangles. The function returns the number of detected objects, so you can retrieve them as in the following example: :: gpu::CascadeClassifier_GPU cascade_gpu(...); Mat image_cpu = imread(...) GpuMat image_gpu(image_cpu); GpuMat objbuf; int detections_number = cascade_gpu.detectMultiScale( image_gpu, objbuf, 1.2, minNeighbors); Mat obj_host; // download only detected number of rectangles objbuf.colRange(0, detections_number).download(obj_host); Rect* faces = obj_host.ptr(); for(int i = 0; i < detections_num; ++i) cv::rectangle(image_cpu, faces[i], Scalar(255)); imshow("Faces", image_cpu); .. seealso:: :ocv:func:`CascadeClassifier::detectMultiScale` .. [Dalal2005] Navneet Dalal and Bill Triggs. *Histogram of oriented gradients for human detection*. 2005.