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自从YOLOv5更新成7.0版本，YOLOv8推出以后，OpenCV4.6以前的版本都无法再加载导出ONNX格式模型了，只有OpenCV4.7以上版本才可以支持最新版本YOLOv5与YOLOv8模型的推理部署。首先看一下最新版本的YOLOv5与YOLOv8的输入与输出格式：
推理演示截图：
ni hao
std::string;
auto net = cv::dnn::readNetFromONNX(onnxpath);
net.setPreferableBackend(cv::dnn::DNN_BACKEND_OPENCV);
net.setPreferableTarget(cv::dnn::DNN_TARGET_CPU);
cv::VideoCapture capture("D:/images/video/sample.mp4");
cv::Mat frame;
while (true) {
bool ret = capture.read(frame);
if (frame.empty()) {
break;
}
int64 start = cv::getTickCount();
// 图象预处理 - 格式化操作
int w = frame.cols;
int h = frame.rows;
int _max = std::max(h, w);
cv::Mat image = cv::Mat::zeros(cv::Size(_max, _max), CV_8UC3);
cv::Rect roi(0, 0, w, h);
frame.copyTo(image(roi));
float x_factor = image.cols / 640.0f;
float y_factor = image.rows / 640.0f;
// 推理
cv::Mat blob = cv::dnn::blobFromImage(image, 1 / 255.0, cv::Size(640, 640), cv::Scalar(0, 0, 0), true, false);
net.setInput(blob);
cv::Mat preds = net.forward();
// 后处理, 1x25200x85
cv::Mat det_output(preds.size[1], preds.size[2], CV_32F, preds.ptr<float>());
float confidence_threshold = 0.5;
std::vector<cv::Rect> boxes;
std::vector<int> classIds;
std::vector<float> confidences;
for (int i = 0; i < det_output.rows; i++) {
float confidence = det_output.at<float>(i, 4);
if (confidence < 0.25) {
continue;
}
cv::Mat classes_scores = det_output.row(i).colRange(5, preds.size[2]);
cv::Point classIdPoint;
double score;
minMaxLoc(classes_scores, 0, &score, 0, &classIdPoint);
// 置信度 0～1之间
if (score > 0.25)
{
float cx = det_output.at<float>(i, 0);
float cy = det_output.at<float>(i, 1);
float ow = det_output.at<float>(i, 2);
float oh = det_output.at<float>(i, 3);
int x = static_cast<int>((cx - 0.5 * ow) * x_factor);
int y = static_cast<int>((cy - 0.5 * oh) * y_factor);
int width = static_cast<int>(ow * x_factor);
int height = static_cast<int>(oh * y_factor);
cv::Rect box;
box.x = x;
box.y = y;
box.width = width;
box.height = height;
boxes.push_back(box);
classIds.push_back(classIdPoint.x);
confidences.push_back(score);
}
}
// NMS
std::vector<int> indexes;
cv::dnn::NMSBoxes(boxes, confidences, 0.25, 0.50, indexes);
for (size_t i = 0; i < indexes.size(); i++) {
int index = indexes;
int idx = classIds[index];
cv::rectangle(frame, boxes[index], colors[idx % 5], 2, 8);
cv::rectangle(frame, cv::Point(boxes[index].tl().x, boxes[index].tl().y - 20),
cv::Point(boxes[index].br().x, boxes[index].tl().y), cv::Scalar(255, 255, 255), -1);
cv::putText(frame, classNames[idx], cv::Point(boxes[index].tl().x, boxes[index].tl().y - 10), cv::FONT_HERSHEY_SIMPLEX, .5, cv::Scalar(0, 0, 0));
}
float t = (cv::getTickCount() - start) / static_cast<float>(cv::getTickFrequency());
putText(frame, cv::format("FPS: %.2f", 1.0 / t), cv::Point(20, 40), cv::FONT_HERSHEY_PLAIN, 2.0, cv::Scalar(255, 0, 0), 2, 8);
char c = cv::waitKey(1);
if (c == 27) {
break;
}
cv::imshow("OpenCV4.8 + YOLOv5", frame);
}
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