为什么cv :: format没有给我预期的结果? [英] Why cv::format is not giving me the expected result?

问题描述

我正在发布模式下使用带有VS 2015的C ++的openCV 3.4.0

I am working with openCV 3.4.0 using C++ with VS 2015 in release mode

我正在尝试将文本放在cv :: Mat中的特定位置.

I am trying to put text on a specific place in the cv::Mat.

当我尝试这样做时，它会起作用:

While I am trying this it works:

    //int FPS = calculate_FPS(measure_time(false));
    int FPS = 6;
    std::cout << "FPS = " << FPS << std::endl;
    measure_time(true);
    cv::putText(canvas(frame_per_second_area), cv::format("FPS: %d", FPS) , cv::Point(frame_per_second_area.width*0.20, frame_per_second_area.height*0.7), cv::FONT_HERSHEY_PLAIN, 1, cv::Scalar(0, 0, 0));

它看起来像:

直到这里一切都很好. 但是，当我尝试这种方式时，会得到不好的结果:

Until here everything is fine. However while I trying this way I get bad results:

    int FPS = calculate_FPS(measure_time(false));
    //int FPS = 6;
    std::cout << "FPS = " << FPS << std::endl;
    measure_time(true);
    cv::putText(canvas(frame_per_second_area), cv::format("FPS: %d", FPS) , cv::Point(frame_per_second_area.width*0.20, frame_per_second_area.height*0.7), cv::FONT_HERSHEY_PLAIN, 1, cv::Scalar(0, 0, 0));

它看起来像:

需要提及的是，屏幕输出看起来不错:

Need to mention that the output to the screen looks good:

需要提及#2-这是函数声明:

Need to mention #2 - This is the function declaration:

int calculate_FPS(double elapsed_time_in_ms);

推荐答案

问题不是在调用:calculate_FPS(measure_time(false));与否.实际的问题是您在同一画布上重复渲染文本.我可以向您演示一下:

The problem is not calling: calculate_FPS(measure_time(false)); or not. The actual problem is that you rendering the text repeatedly on the same canvas. I can demonstrate this to you:

canvas = np.ones((100, 200, 3), dtype=np.uint8)

# Set the canvas background color as Red.
canvas[:, :] = np.array([0, 0, 255])

for i in xrange(15):
    cv2.putText(canvas, "FPS: " + str(i), (50, 70), cv2.FONT_HERSHEY_PLAIN, 1, np.array([0, 0, 0]))

canvas = np.ones((100, 200, 3), dtype=np.uint8)

# Set the canvas background color as Red.
canvas[:, :] = np.array([0, 0, 255])

for i in xrange(15):
    canvas[:, :] = np.array([0, 0, 255])
    cv2.putText(canvas, "FPS: " + str(i), (50, 70), cv2.FONT_HERSHEY_PLAIN, 1, np.array([0, 0, 0]))

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