代码

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

#define ERROR_OUT__ std::cerr<<"[ERROR][File:"<<__FILE__<<"][Line:"<<__LINE__<<"]"

#ifndef _DEBUG
#define TB__(A) int64 A; A = cv::getTickCount()
#define TE__(A) std::cout << #A << " : " << 1.E3 * double(cv::getTickCount() - A)/double(cv::getTickFrequency()) << "ms" << std::endl
#else
#define TB__(A)
#define TE__(A)
#endif

class Print{
public:
    static void min_max_loc(cv::Mat &src){
        std::vector<cv::Mat> mats;
        cv::split(src, mats);
        for (size_t c = 0; c < mats.size(); c++){
            double min_val, max_val;
            cv::Point min_loc, max_loc;
            cv::minMaxLoc(mats[c], &min_val, &max_val, &min_loc, &max_loc);
            printf("channel %d, minv %6.6f, maxv %6.6f, minl [%6d, %6d], maxl [%6d, %6d]\n", \
                c, min_val, max_val, min_loc.x, min_loc.y, max_loc.x, max_loc.y);
        }
    }
};

int main(){
    cv::Mat image, cielab, cielabf;
    image.create(720, 1280, CV_8UC3);
    TB__(__randomu);
    cv::randu(image, cv::Scalar::all(0), cv::Scalar::all(256));
    TE__(__randomu);

    // warming up
    cv::cvtColor(image, cielab, CV_BGR2Lab);
    TB__(__bgr2lab_8UC3);
    cv::cvtColor(image, cielab, CV_BGR2Lab);
    cielab.convertTo(cielabf, CV_32FC3);
    TE__(__bgr2lab_8UC3);
    Print::min_max_loc(cielabf);


    image.convertTo(image, CV_32FC3, 1. / 255.);
    // warming up
    cv::cvtColor(image, cielabf, CV_BGR2Lab);
    TB__(__bgr2lab_32FC3);
    cv::cvtColor(image, cielabf, CV_BGR2Lab);
    TE__(__bgr2lab_32FC3);

    Print::min_max_loc(cielabf);

    return 0;
}

---

测试平台及输出

CPU : i5-4590 @3.3GHz

输出：

__randomu : 2.13923ms
__bgr2lab_8UC3 : 5.99754ms
channel 0, minv 0.000000, maxv 255.000000, minl [   460,    420], maxl [   410,    106]
channel 1, minv 42.000000, maxv 226.000000, minl [   170,     27], maxl [  1260,     43]
channel 2, minv 20.000000, maxv 222.000000, minl [    61,    223], maxl [   640,     10]
__bgr2lab_32FC3 : 17.1545ms
channel 0, minv 0.019787, maxv 99.877167, minl [   460,    420], maxl [   410,    106]
channel 1, minv -86.124870, maxv 97.908821, minl [   826,    581], maxl [   181,    276]
channel 2, minv -107.861755, maxv 94.271385, minl [   520,    399], maxl [   839,     96]