As known, OpenCV 3.0 supports new class cv::Umat which provides Transparent API (TAPI) to use OpenCL automaticaly if it can: http://code.opencv.org/projects/opencv/wiki/Opencv3#tapi
There are two indtroductions to the cv::Umat and TAPI:
But if I have:
- Intel CPU Core i5 (Haswell) 4xCores (OpenCL Intel CPUs with SSE 4.1, SSE 4.2 or AVX support)
- Intel Integrated HD Graphics which supports OpenCL 1.2
- 1st nVidia GPU GeForce GTX 970 (Maxwell) which supports OpenCL 1.2 and CUDA
- 2nd nVidia GPU GeForce GTX 970 ...
If I turn on OpenCL in OpenCV, then how can I change the device on wich OpenCL-code will be executed: on 8 Cores of CPU, on Integrated HD Graphics, on 1st nVidia GPU or 2nd nVidia GPU?
How can I select one of each of these 4 devices to use OpenCL for parallel execution algorithms with cv::Umat?
For example, how can I use OpenCL acceleration on 4xCores of CPU Core-i5 with cv::Umat?
I use something like this to check versions and hardware being used for OpenCL support.
ocl::setUseOpenCL(true); if (!ocl::haveOpenCL()) { cout << "OpenCL is not available..." << endl; //return; } cv::ocl::Context context; if (!context.create(cv::ocl::Device::TYPE_GPU)) { cout << "Failed creating the context..." << endl; //return; } cout << context.ndevices() << " GPU devices are detected." << endl; //This bit provides an overview of the OpenCL devices you have in your computer for (int i = 0; i < context.ndevices(); i++) { cv::ocl::Device device = context.device(i); cout << "name: " << device.name() << endl; cout << "available: " << device.available() << endl; cout << "imageSupport: " << device.imageSupport() << endl; cout << "OpenCL_C_Version: " << device.OpenCL_C_Version() << endl; cout << endl; }
Then you can set your preferred hardware to use, using this
cv::ocl::Device(context.device(1));
Hope this helps you.
You can also set a desired OpenCL device from within your code using environment variable method as follows (example is first GPU device):
if (putenv("OPENCV_OPENCL_DEVICE=:GPU:0") != 0 || !cv::ocl::useOpenCL()) { std::cerr << "Failed to set a desired OpenCL device" << std::endl; std::cerr << "Press any key to exit..." << std::endl; getchar(); return 1; }
Call to cv::ocl::useOpenCL() will force OpenCV to setup a default OpenCL device to the one specified in the environment variable OPENCV_OPENCL_DEVICE which is setup prior to that call.
I checked that this actually happens by setting a break-point at opencv_core310d.dll!cv::ocl::selectOpenCLDevice() Line 2256 (opencv\source\modules\core\src\ocl.cpp):
static cl_device_id selectOpenCLDevice() { std::string platform, deviceName; std::vector<:string bdsfid="494"> deviceTypes; const char* configuration = getenv("OPENCV_OPENCL_DEVICE"); if (configuration && (strcmp(configuration, "disabled") == 0 || !parseOpenCLDeviceConfiguration(std::string(configuration), platform, deviceTypes, deviceName) )) return NULL;
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