#include <opencv2/opencv.hpp>

#include <iostream>

using namespace cv;

using namespace std;

int main(int argc, char** argv)

{

    Mat src = imread("f:/images/butterfly.jpg");

    if (src.empty())

    {

        printf("Could not find the image!\n");

        return -1;

    }

    namedWindow("input", WINDOW_AUTOSIZE);

    imshow("input", src);

    vector<Mat> mv;

    split(src, mv);

    // 计算直方图

    int histSize = 256;

    float range[] = { 0, 255 };

    const float* histRanges = { range };

    Mat b_hist, g_hist, r_hist;

    calcHist(&mv[0], 1, 0, Mat(), b_hist, 1, &histSize, &histRanges, true, false);

    calcHist(&mv[1], 1, 0, Mat(), g_hist, 1, &histSize, &histRanges, true, false);

    calcHist(&mv[2], 1, 0, Mat(), r_hist, 1, &histSize, &histRanges, true, false);

    Mat result = Mat::zeros(Size(600, 400), CV_8UC3);

    int margin = 50;

    int maxValue = result.rows - 2 * margin;

    // 归一化

    normalize(b_hist, b_hist, 0, maxValue, NORM_MINMAX, -1, Mat());

    normalize(g_hist, g_hist, 0, maxValue, NORM_MINMAX, -1, Mat());

    normalize(r_hist, r_hist, 0, maxValue, NORM_MINMAX, -1, Mat());

    float step = 500.0 / 256.0;

    // 绘制直方图

    for (int i = 0; i < 255; i++) {

        float bh1 = b_hist.at<float>(i, 0);

        float gh1 = g_hist.at<float>(i, 0);

        float rh1 = r_hist.at<float>(i, 0);

        float bh2 = b_hist.at<float>(i + 1, 0);

        float gh2 = g_hist.at<float>(i + 1, 0);

        float rh2 = r_hist.at<float>(i + 1, 0);

        line(result,

            Point(step * i + margin, maxValue + 50 - bh1),

            Point(step * (i + 1) + margin, maxValue + 50 - bh2),

            Scalar(255, 0, 0), 1, 8, 0);

        line(result,

            Point(step * i + margin, maxValue + 50 - gh1),

            Point(step * (i + 1) + margin, maxValue + 50 - gh2),

            Scalar(0, 255, 0), 1, 8, 0);

        line(result,

            Point(step * i + margin, maxValue + 50 - rh1),

            Point(step * (i + 1) + margin, maxValue + 50 - rh2),

            Scalar(0, 0, 255), 1, 8, 0);

    }

    imshow("result", result);

    waitKey(0);

    destroyAllWindows();

}

函数抽取：

void show_hist(string name, Mat src) {

    vector<Mat> mv;

    split(src, mv);

    // 计算直方图

    int histSize = 256;

    float range[] = { 0, 255 };

    const float* histRanges = { range };

    Mat b_hist, g_hist, r_hist;

    calcHist(&mv[0], 1, 0, Mat(), b_hist, 1, &histSize, &histRanges, true, false);

    calcHist(&mv[1], 1, 0, Mat(), g_hist, 1, &histSize, &histRanges, true, false);

    calcHist(&mv[2], 1, 0, Mat(), r_hist, 1, &histSize, &histRanges, true, false);

    Mat result = Mat::zeros(Size(600, 400), CV_8UC3);

    int margin = 50;

    int maxValue = result.rows - 2 * margin;

    // 归一化

    normalize(b_hist, b_hist, 0, maxValue, NORM_MINMAX, -1, Mat());

    normalize(g_hist, g_hist, 0, maxValue, NORM_MINMAX, -1, Mat());

    normalize(r_hist, r_hist, 0, maxValue, NORM_MINMAX, -1, Mat());

    float step = 500.0 / 256.0;

    // 绘制直方图

    for (int i = 0; i < 255; i++) {

        float bh1 = b_hist.at<float>(i, 0);

        float gh1 = g_hist.at<float>(i, 0);

        float rh1 = r_hist.at<float>(i, 0);

        float bh2 = b_hist.at<float>(i + 1, 0);

        float gh2 = g_hist.at<float>(i + 1, 0);

        float rh2 = r_hist.at<float>(i + 1, 0);

        line(result,

            Point(step * i + margin, maxValue + 50 - bh1),

            Point(step * (i + 1) + margin, maxValue + 50 - bh2),

            Scalar(255, 0, 0), 1, 8, 0);

        line(result,

            Point(step * i + margin, maxValue + 50 - gh1),

            Point(step * (i + 1) + margin, maxValue + 50 - gh2),

            Scalar(0, 255, 0), 1, 8, 0);

        line(result,

            Point(step * i + margin, maxValue + 50 - rh1),

            Point(step * (i + 1) + margin, maxValue + 50 - rh2),

            Scalar(0, 0, 255), 1, 8, 0);

    }

    imshow(name, result);

}