Using DepthAI Hardware / OAK depth sensors

Table of Contents

• Source code

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Oak-D and Oak-D-Light cameras

Depth sensors compatible with Luxonis DepthAI library are supported through OpenCV Graph API (or G-API) module. RGB image and some other formats of output can be retrieved by using familiar interface of G-API module.

In order to use DepthAI sensor with OpenCV you should do the following preliminary steps:

1. Install Luxonis DepthAI library depthai-core.
2. Configure OpenCV with DepthAI library support by setting WITH_OAK flag in CMake. If DepthAI library is found in install folders OpenCV will be built with depthai-core (see a status WITH_OAK in CMake log).
3. Build OpenCV.

Source code

You can find source code how to process heterogeneous graphs in the modules/gapi/samples/oak_basic_infer.cpp of the OpenCV source code library.

C++

#include <algorithm>
#include <iostream>
#include <sstream>
 
#include <opencv2/imgproc.hpp>
#include <opencv2/imgcodecs.hpp>
#include <opencv2/gapi.hpp>
#include <opencv2/gapi/core.hpp>
#include <opencv2/gapi/imgproc.hpp>
#include <opencv2/gapi/infer.hpp>
#include <opencv2/gapi/infer/parsers.hpp>
#include <opencv2/gapi/render.hpp>
#include <opencv2/gapi/cpu/gcpukernel.hpp>
#include <opencv2/highgui.hpp>
 
#include <opencv2/gapi/oak/oak.hpp>
#include <opencv2/gapi/oak/infer.hpp>
 
const std::string keys =
    "{ h help              |             | Print this help message }"
    "{ detector            |             | Path to compiled .blob face detector model }"
    "{ duration            | 100         | Number of frames to pull from camera and run inference on }";
 
namespace custom {
 
G_API_NET(FaceDetector, <cv::GMat(cv::GFrame)>, "sample.custom.face-detector");
 
using GDetections = cv::GArray<cv::Rect>;
using GSize       = cv::GOpaque<cv::Size>;
using GPrims      = cv::GArray<cv::gapi::wip::draw::Prim>;
 
G_API_OP(BBoxes, <GPrims(GDetections)>, "sample.custom.b-boxes") {
    static cv::GArrayDesc outMeta(const cv::GArrayDesc &) {
        return cv::empty_array_desc();
    }
};
 
GAPI_OCV_KERNEL(OCVBBoxes, BBoxes) {
    // This kernel converts the rectangles into G-API's
    // rendering primitives
    static void run(const std::vector<cv::Rect> &in_face_rcs,
                          std::vector<cv::gapi::wip::draw::Prim> &out_prims) {
        out_prims.clear();
        const auto cvt = [](const cv::Rect &rc, const cv::Scalar &clr) {
            return cv::gapi::wip::draw::Rect(rc, clr, 2);
        };
        for (auto &&rc : in_face_rcs) {
            out_prims.emplace_back(cvt(rc, CV_RGB(0,255,0))); // green
        }
    }
};
 
} // namespace custom
 
int main(int argc, char *argv[]) {
    cv::CommandLineParser cmd(argc, argv, keys);
    if (cmd.has("help")) {
        cmd.printMessage();
        return 0;
    }
 
    const auto det_name = cmd.get<std::string>("detector");
    const auto duration = cmd.get<int>("duration");
 
    if (det_name.empty()) {
        std::cerr << "FATAL: path to detection model is not provided for the sample."
                  << "Please specify it with --detector options."
                  << std::endl;
        return 1;
    }
 
    // Prepare G-API kernels and networks packages:
    auto detector = cv::gapi::oak::Params<custom::FaceDetector>(det_name);
    auto networks = cv::gapi::networks(detector);
 
    auto kernels = cv::gapi::combine(
        cv::gapi::kernels<custom::OCVBBoxes>(),
        cv::gapi::oak::kernels());
 
    auto args = cv::compile_args(kernels, networks);
 
    // Initialize graph structure
    cv::GFrame in;
    cv::GFrame copy = cv::gapi::oak::copy(in); // NV12 transfered to host + passthrough copy for infer
    cv::GOpaque<cv::Size> sz = cv::gapi::streaming::size(copy);
 
    // infer is not affected by the actual copy here
    cv::GMat blob = cv::gapi::infer<custom::FaceDetector>(copy);
    // FIXME: OAK infer detects faces slightly out of frame bounds
    cv::GArray<cv::Rect> rcs = cv::gapi::parseSSD(blob, sz, 0.5f, true, false);
    auto rendered = cv::gapi::wip::draw::renderFrame(copy, custom::BBoxes::on(rcs));
    // on-the-fly conversion NV12->BGR
    cv::GMat out = cv::gapi::streaming::BGR(rendered);
 
    auto pipeline  = cv::GComputation(cv::GIn(in), cv::GOut(out, rcs))
        .compileStreaming(std::move(args));
 
    // Graph execution
    pipeline.setSource(cv::gapi::wip::make_src<cv::gapi::oak::ColorCamera>());
    pipeline.start();
 
    cv::Mat out_mat;
    std::vector<cv::Rect> out_dets;
    int frames = 0;
    while (pipeline.pull(cv::gout(out_mat, out_dets))) {
        std::string name = "oak_infer_frame_" + std::to_string(frames) + ".png";
 
        cv::imwrite(name, out_mat);
 
        if (!out_dets.empty()) {
            std::cout << "Got " << out_dets.size() << " detections on frame #" << frames << std::endl;
        }
 
        ++frames;
        if (frames == duration) {
            pipeline.stop();
            break;
        }
    }
    std::cout << "Pipeline finished. Processed " << frames << " frames" << std::endl;
    return 0;
}