1.创建纯色图片

cv::Mat mat(100, 100, CV_8UC3);
int es = mat.elemSize(); // 单个数据大小
int size = mat.rows * mat.cols * es; // 所有数据大小

for (int i = 0; i < size; i +=es){
    mat.data[i] = 0; // Blue
    mat.data[i + 1] = 0; // Green
    mat.data[i + 2] = 0; // Red
}
cv::imwrite("cv_blue.jpg",mat);

2.opencv颜色转换(RGB-HSV)
opencv中HSV的取值范围：H:[0,180],S:[0,255],V:[0,255]

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

int main() {
    //std::cout << cv::getVersionString() << std::endl;
    cv::Mat image = cv::imread("cv_blue.jpg");
    cv::cvtColor(image,image,CV_BGR2RGB);

    /**
     * H: [0,180],S:[0,255],V:[0,255]
     */
    cv::Mat temp = image.clone();
    cv::cvtColor(temp,temp,CV_RGB2HSV);
    int h = temp.at<cv::Vec3b>(0,0)[0];
    int s = temp.at<cv::Vec3b>(0,0)[1];
    int v = temp.at<cv::Vec3b>(0,0)[2];
    std::cout << "h:" << h / 180.0 << ", s:" << s / 255.0<<", v:" << v / 255.0 << std::endl;

    int red = static_cast<int>(image.at<cv::Vec3b>(0,0)[0]);
    int green = static_cast<int>(image.at<cv::Vec3b>(0,0)[1]);
    int blue = static_cast<int>(image.at<cv::Vec3b>(0,0)[2]);
    std::cout << "red:" << red << ", green:" << green <<", blue:" << blue << std::endl;
}

h:0.666667, s:1, v:0.996078
red:0, green:0, blue:254

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