OpenCV：断言失败

Question

I get this type of error when I try to use the adaptiveThreshold() function. What could have gone wrong?

here is my code:

int main()
{
    try 
    {
        cv::Mat img = cv::imread("rubikscube.png");
        cv::Mat thres_final;
        cv::Mat adap_thres_final;

        cv::threshold(img, thres_final, 0, 255, CV_THRESH_BINARY);
        cv::adaptiveThreshold(img, adap_thres_final, 255, CV_ADAPTIVE_THRESH_GAUSSIAN_C, CV_THRESH_BINARY, 11, 2);

        cv::namedWindow("Source");
        cv::imshow("Source", img);

        cv::namedWindow("Threshold");
        cv::imshow("Threshold", thres_final);

        cv::namedWindow("Adaptive Threshold");
        cv::imshow("Adaptive Threshold", adap_thres_final);

        cv::waitKey(0);

    }
    catch (...)
    {
        std::cout << "Exception Occured! \n";
    }

    return 0;
}

Answer 1

When I run this code on my machine, I get the following error

OpenCV Error: Assertion failed (src.type() == CV_8UC1) in adaptiveThreshold, file /Users/lakshayg/dev/opencv/modules/imgproc/src/thresh.cpp, line 795

adaptiveThreshold accepts images of type CV_8UC1 but the one you are passing is CV_8UC3 .

One way of fixing this would be to read the image as grayscale in the first place.

The imread call with change to

cv::Mat img = cv::imread("rubikscube.png", CV_LOAD_IMAGE_GRAYSCALE);

The CV_LOAD_IMAGE_GRAYSCALE here directs the function to read the image as grayscale.