yolov8训练完成的模型转成ncnn的模型后，推理不出结果，网上查了说要进行前后处理，确实不会，能发个cpp的例子看看么！ about ncnn HOT 4 OPEN

ex.input("images", bgr);

std::vector<Object> proposals;

ncnn::Mat out;
ex.extract("output", out);
//std::cout << "out dims: " << out.dims << " w: " << out.w << " h: " << out.h << " d: " << out.d << " c: " << out.c << std::endl;

// output shape: [1, 84, 8400]; 84 means: [cx, cy, w, h, prob * 80]
cv::Mat output_buffer(out.h, out.w, CV_32F, (float*)out.data);
transpose(output_buffer, output_buffer); // [8400,84]
//std::cout << "rows : " << output_buffer.rows << " cols: " << output_buffer.cols << std::endl;

float score_threshold = prob_threshold;
std::vector<int> class_ids;
std::vector<float> class_scores;
std::vector<Rect> boxes;

// Figure out the bbox, class_id and class_score
for (int i = 0; i < output_buffer.rows; i++) {
    Mat classes_scores = output_buffer.row(i).colRange(4, 84);
    Point class_id;
    double maxClassScore;
    minMaxLoc(classes_scores, 0, &maxClassScore, 0, &class_id);

    if (maxClassScore > score_threshold) {
        class_scores.push_back(maxClassScore);
        class_ids.push_back(class_id.x);
        float cx = output_buffer.at<float>(i, 0);
        float cy = output_buffer.at<float>(i, 1);
        float w = output_buffer.at<float>(i, 2);
        float h = output_buffer.at<float>(i, 3);

        int left = int((cx - 0.5 * w) * scale);
        int top = int((cy - 0.5 * h) * scale);
        int width = int(w * scale);
        int height = int(h * scale);

        // printf("box: {%d, %d, %d, %d}, class_idx: %d, score: %f\n", left, top, left + width, top + height, class_id.x, maxClassScore);
        boxes.push_back(Rect(left, top, width, height));
    }
}
//NMS
std::vector<int> indices;
NMSBoxes(boxes, class_scores, score_threshold, nms_threshold, indices);

for (size_t i = 0; i < indices.size(); i++) {
    Object obj;
    int index = indices[i];
    obj.label = class_ids[index];
    obj.prob = class_scores[index];
    obj.rect.x = boxes[index].x;
    obj.rect.y = boxes[index].y;
    obj.rect.width = boxes[index].width;
    obj.rect.height = boxes[index].height;
    objects.push_back(obj);

    printf("### box: {%f, %f, %f, %f}, class_idx: %d, score: %f\n", obj.rect.x, obj.rect.y, obj.rect.x + obj.rect.width, obj.rect.y + obj.rect.height, obj.label, obj.prob);
}