OpenCV4入门080：图像直方图动态调整参数均衡化

入门系列索引：OpenCV入门索引目录

此程序结合滚动条的创建，演示了如何用calcHist来创建直方图。可以条件滚动条，看到不同形态的图像直方图。

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//---------------------------------【头文件、命名空间包含部分】----------------------------
//      描述：包含程序所使用的头文件和命名空间
//------------------------------------------------------------------------------------------------
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
using namespace cv;
using namespace std;

//-----------------------------------【全局变量声明部分】---------------------------------------
//      描述：声明全局变量
//---------------------------------------------------------------------------------------------------
int _brightness = 100;
int _contrast   = 100;
Mat image;

/* brightness/contrast callback function */
static void updateBrightnessContrast(int /*arg*/, void *) {
    int histSize   = 64;
    int brightness = _brightness - 100;
    int contrast   = _contrast - 100;

    /*
     * The algorithm is by Werner D. Streidt
     * (http://visca.com/ffactory/archives/5-99/msg00021.html)
     */
    double a, b;
    if (contrast > 0) {
        double delta = 127. * contrast / 100;
        a            = 255. / (255. - delta * 2);
        b            = a * (brightness - delta);
    } else {
        double delta = -128. * contrast / 100;
        a            = (256. - delta * 2) / 255.;
        b            = a * brightness + delta;
    }

    Mat dst, hist;
    image.convertTo(dst, CV_8U, a, b);
    imshow("image", dst);

    calcHist(&dst, 1, 0, Mat(), hist, 1, &histSize, 0);
    Mat histImage = Mat::ones(200, 320, CV_8U) * 255;

    normalize(hist, hist, 0, histImage.rows, NORM_MINMAX, CV_32F);

    histImage = Scalar::all(255);
    int binW  = cvRound((double)histImage.cols / histSize);

    for (int i = 0; i < histSize; i++)
        rectangle(histImage, Point(i * binW, histImage.rows),
                  Point((i + 1) * binW, histImage.rows - cvRound(hist.at<float>(i))),
                  Scalar::all(0), -1, 8, 0);
    imshow("histogram", histImage);
}

//-----------------------------------【main( )函数】--------------------------------------------
//      描述：控制台应用程序的入口函数，我们的程序从这里开始
//-------------------------------------------------------------------------------------------------
int main(int argc, const char **argv) {
    image = imread("1.png", 1);
    imshow("src", image);

    // 载入原始图
    image = imread("1.png", 0);
    imshow("gray", image);

    namedWindow("image", 0);
    namedWindow("histogram", 0);

    createTrackbar("brightness", "image", &_brightness, 200, updateBrightnessContrast);
    createTrackbar("contrast", "image", &_contrast, 200, updateBrightnessContrast);

    updateBrightnessContrast(0, 0);
    waitKey();

    return 0;
}
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