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[C++] Using DNN with Tiny Yolo v2, not getting 13x13 (just 125 x 1)

Hey all,

I'm trying to use this model as a test reference: https://github.com/onnx/models/tree/master/vision/object_detection_segmentation/tiny_yolov2

They claim the output is supposed to be a 1x125x13x13 but I'm not sure I'm getting that...

My OpenCV version is 4.1.1.

I can see that I get a [125 x 1] but I'm not sure where the 13x13 is supposed to come from or how I'm supposed to process these results into getting the bounding box data...

Here's my code below:

#include <opencv2/dnn/dnn.hpp>
#include <opencv2/imgcodecs.hpp>
#include <opencv2/imgproc.hpp>

#include <gsl/span>

#include <vector>
#include <iostream>
#include <cassert>

int main()
{
    auto img = cv::imread("/home/christian/Downloads/horse.jpg");

    assert(img.channels() == 3);
    assert(img.depth() == CV_8U);

    img.convertTo(img, CV_32F);
    cv::resize(img, img, cv::Size(416, 416));

    assert(img.cols == 416);
    assert(img.rows == 416);
    assert(img.channels() == 3);
    assert(img.depth() == CV_32F);

    auto model = cv::String("/home/christian/Downloads/tiny_yolov2 (1)/tiny_yolov2/model.onnx");
    auto net   = cv::dnn::readNet(model);

    auto outLayers    = net.getUnconnectedOutLayers();
    auto outLayerType = net.getLayer(outLayers[0])->type;
    std::cout << "layer type is : " << outLayerType << "\n";

    auto layerNames = net.getLayerNames();
    std::cout << layerNames.size() << "\n";
    for (auto const& name : layerNames)
    {
        std::cout << name << "\n";
    }

    auto blob = cv::Mat();
    cv::dnn::blobFromImage(img, blob, 1.0 / 255, cv::Size(416, 416), cv::Scalar(0, 0, 0), true, false, CV_32F);

    net.setInput(blob);

    auto outs = std::vector<std::vector<cv::Mat>>();
    outs.resize(13);
    for (auto& out : outs)
    {
        out.resize(13);
    }

    auto outNames = net.getUnconnectedOutLayersNames();
    net.forward(outs, outNames);

    for (auto const& out : outs)
    {
        std::cout << out.size() << "\n";
        auto& o = out[0];
        std::cout << o.size() << "\n";
        std::cout << o.rows << ", " << o.cols << "\n";
    }

    return 0;
}