BGR转HSV，然后再次返回 [英] BGR to HSV and back again

问题描述

文档似乎并未解释HSV-> BGR转换的预期输入范围.这是一些示例代码，在该示例中，我尝试将原始BGR值转换为HSV后取回.有谁知道预期的缩放比例?

The documentation does not seem to explain what the expected range of the input is for an HSV->BGR conversion. Here is some example code where I am trying to get back the original BGR value after converting it to HSV. Does anyone know which scaling is expected?

#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;
}

推荐答案

函数HSVtoBGR中存在一些缩放问题.

You have some scaling problems in the function HSVtoBGR.

您需要将转换后而不是转换后的结果乘以255.请记住，类型CV_32F和CV_8U的Mat会发生不同的转换.

You need to multiply by 255 the result after the conversion, not before. Remember that different conversions take place for Mat of type CV_32F and CV_8U.

这应该可以正常工作:

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);
}

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