c++ - BGR 到 HSV 并再次返回

Question

文档似乎没有解释 HSV->BGR 转换的预期输入范围。这是一些示例代码，我试图在将其转换为 HSV 后取回原始 BGR 值。有谁知道预期的缩放比例？

#include <iostream>

#include <opencv2/opencv.hpp>

cv::Vec3b HSVtoBGR(const cv::Vec3f& hsv)
{
    cv::Vec3f hsvAdjusted = hsv; // If we use this directly, the output is (0,0,1) which is very wrong
    //hsvAdjusted[0] *= 360.; // If we do this to bring all of the values into the range (0,1), the output is (0,1,0), which is also very wrong

    // If we do this to bring all of the values into the range (0,255), the output is (0,0,200), which is still very wrong
    hsvAdjusted[1] *= 255./360.;
    hsvAdjusted[1] *= 255.;
    hsvAdjusted[2] *= 255.;

    cv::Mat_<cv::Vec3f> hsvMat(hsvAdjusted);

    cv::Mat_<cv::Vec3f> bgrMat;

    cv::cvtColor(hsvMat, bgrMat, CV_HSV2BGR);

    cv::Vec3b bgr = static_cast<cv::Vec3b>(bgrMat(0,0));
    return bgr;
}

/** Input 0 <= B <= 255, 0 <= G <= 255, 0 <= R <= 255
  * Output 0 <= H <= 360, 0 <= S <= 1, 0 <= V <= 1  */
cv::Vec3f BGRtoHSV(const cv::Vec3b& bgr)
{
    cv::Mat3f bgrMat(static_cast<cv::Vec3f>(bgr));

    bgrMat *= 1./255.;

    cv::Mat3f hsvMat;
    cv::cvtColor(bgrMat, hsvMat, CV_BGR2HSV);

    cv::Vec3f hsv = hsvMat(0,0);

    return hsv;
}

int main()
{
    // Create a BGR color
    cv::Vec3b bgr(5, 100, 200);
    std::cout << "bgr: " << bgr << std::endl;

    // Convert BGR to HSV
    cv::Vec3f hsv = BGRtoHSV(bgr);
    std::cout << "hsv: " << hsv << std::endl; // outputs // (29.23, .976, .7843), which seems correct

    // Convert back from HSV to BGR
    cv::Vec3b bgr2 = HSVtoBGR(hsv);
    std::cout << "bgr2: " << bgr2 << std::endl;

    return 0;
}

Answer 1

函数 HSVtoBGR 中存在一些缩放问题。

您需要将转换后的结果乘以 255，而不是之前。请记住，CV_32F 和 CV_8U 类型的 Mat 会发生不同的转换。

这应该按预期工作:

cv::Vec3b HSVtoBGR(const cv::Vec3f& hsv)
{
    cv::Mat_<cv::Vec3f> hsvMat(hsv);
    cv::Mat_<cv::Vec3f> bgrMat;

    cv::cvtColor(hsvMat, bgrMat, CV_HSV2BGR);

    bgrMat *= 255; // Upscale after conversion

    // Conversion to Vec3b is handled by OpenCV, no need to static_cast
    return bgrMat(0);
}