Poor performance of cv::text

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I need to locate all letters on this screenshot:

Tried https://github.com/opencv/opencv_cont...

(playing with params of NMSBoxes didn't give me any good result)

and this one: https://github.com/opencv/opencv_cont...

(also played with different parameters several hours with no luck).

However trivial operations with tresholding and connected components can give relatively good results (code taken from stackoverflow):

    Mat large = imread(INPUT_FILE);
Mat rgb;
pyrDown(large, rgb);
Mat small;
cvtColor(rgb, small, CV_BGR2GRAY);
Mat grad;
Mat morphKernel = getStructuringElement(MORPH_ELLIPSE, Size(3, 3));
morphologyEx(small, grad, MORPH_GRADIENT, morphKernel);
imshow("grd", grad);
imshow("sml", small);
Mat bw;
threshold(grad, bw, 0.0, 255.0, THRESH_BINARY | THRESH_OTSU);
Mat connected;
morphKernel = getStructuringElement(MORPH_RECT, Size(9, 1));
morphologyEx(bw, connected, MORPH_CLOSE, morphKernel);
imshow("xx", connected);
Mat mask = Mat::zeros(bw.size(), CV_8UC1);
vector<vector<Point>> contours;
vector<Vec4i> hierarchy;
findContours(connected, contours, hierarchy, CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE, Point(0, 0));
for (int idx = 0; idx >= 0; idx = hierarchy[idx][0]) {
    Rect rect = boundingRect(contours[idx]);
    Mat maskROI(mask, rect);
    maskROI = Scalar(0, 0, 0);
    drawContours(mask, contours, idx, Scalar(255, 255, 255), CV_FILLED);
    double r = (double)countNonZero(maskROI) / (rect.width*rect.height);
    if (r > .45 
        &&
        (rect.height > 8 && rect.width > 8) 
        ) {
        rectangle(rgb, rect, Scalar(0, 255, 0), 2);
    }
}
imshow("res",rgb);

so what is wrong with samples from cv::text?