Opencv4中drawContours函数只能绘制出蓝色的线

Question

color中只有蓝色的通道调整有用，红色和绿色怎么调都没有作用，不知道这是为什么？

#include <opencv2/opencv.hpp>
#include <string>
#include <iostream>

std::string Type2String(int type)
{
    std::string strType;
    uchar depth = type & CV_MAT_DEPTH_MASK;
    uchar chans = 1 + (type >> CV_CN_SHIFT);
    switch (depth)
    {
    case CV_8U:
        strType = "CV_8U"; break;
    case CV_8S:
        strType = "CV_8S"; break;
    case CV_16U:
        strType = "CV_16U"; break;
    case CV_16S:
        strType = "CV_16S"; break;
    case CV_32S:
        strType = "CV_32S"; break;
    case CV_32F:
        strType = "CV_32F"; break;
    case CV_64F:
        strType = "CV_64F"; break;
    default:
        strType = "UNKNOWN_TYPE"; break;
    }
    strType += "C";
    strType += (chans + '0');

    return strType;
}

int main()
{
    cv::Mat segmentation = cv::imread("D:/Desktop/轮廓test/segmentation.jpg");

    if (segmentation.empty())
    {
        std::cout << "图片为空" << std::endl;
        return 1;
    }

    std::cout << "segmentation：" << Type2String(segmentation.type()) << std::endl;

    cv::Mat segmentation_gary;
    cvtColor(segmentation, segmentation_gary, cv::COLOR_BGR2GRAY);

    std::cout << "segmentation_gary：" << Type2String(segmentation_gary.type()) << std::endl;

    std::vector< std::vector<cv::Point> > contours;
    std::vector<cv::Vec4i> hierarchy;
    
    findContours(segmentation_gary, contours, hierarchy, cv::RETR_EXTERNAL, cv::CHAIN_APPROX_SIMPLE, cv::Point(0, 0));

    std::cout << "segmentation：" << Type2String(segmentation.type()) << std::endl;

    for (size_t i = 0; i < contours.size(); i++)
    {
        cv::Scalar color = (255, 0, 255);
        drawContours(segmentation, contours, i, color, 5, 8, hierarchy, 0, cv::Point(0, 0));
    }
    imshow("轮廓", segmentation);

    cv::waitKey();
    return 0;
}

这是原图

这是运行结果（如果蓝色通道为0，其他通道为任何值都不显示线条）

Answer 1

试试：
Scalar color( rand()&255, rand()&255, rand()&255 );