三 (3.2 imgproc) 图像直方图

直方图均衡化 — OpenCV 2.3.2 documentation http://www.opencv.org.cn/opencvdoc/2.3.2/html/doc/tutorials/imgproc/histograms/histogram_equalization/histogram_equalization.html#histogram-equalization

图像的直方图是什么?

• 直方图是图像中像素强度分布的图形表达方式.
• 它统计了每一个强度值所具有的像素个数.

直方图均衡化

#include "pch.h"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include 
#include 

using namespace cv;
using namespace std;

/**  @function main */
int main(int argc, char** argv)
{
    Mat src, dst;

    const char* source_window = "Source image";
    const char* equalized_window = "Equalized Image";

    /// 加载源图像
    src = imread("test.jpg", 1);

    if (!src.data)
    {
        cout << "Usage: ./Histogram_Demo " << endl;
        return -1;
    }

    resize(src, src,Size(500,500));
    /// 转为灰度图
    cvtColor(src, src, CV_BGR2GRAY);

    /// 应用直方图均衡化
    equalizeHist(src, dst);

    /// 显示结果
    namedWindow(source_window, CV_WINDOW_AUTOSIZE);
    namedWindow(equalized_window, CV_WINDOW_AUTOSIZE);

    imshow(source_window, src);
    imshow(equalized_window, dst);

    /// 等待用户按键退出程序
    waitKey(0);

    return 0;
}

直方图计算

#include "pch.h"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include 
#include 

using namespace std;
using namespace cv;

/** @函数 main */
int main(int argc, char** argv)
{
    Mat src, dst;

    /// 装载图像
    src = imread("test.jpg", 1);

    if (!src.data)
    {
        return -1;
    }

    /// 分割成3个单通道图像 ( R, G 和 B )
    vector rgb_planes;
    split(src, rgb_planes);

    /// 设定bin数目
    int histSize = 255;

    /// 设定取值范围 ( R,G,B) )
    float range[] = { 0, 255 };
    const float* histRange = { range };

    bool uniform = true; bool accumulate = false;

    Mat r_hist, g_hist, b_hist;

    /// 计算直方图:
    calcHist(&rgb_planes[0], 1, 0, Mat(), r_hist, 1, &histSize, &histRange, uniform, accumulate);
    calcHist(&rgb_planes[1], 1, 0, Mat(), g_hist, 1, &histSize, &histRange, uniform, accumulate);
    calcHist(&rgb_planes[2], 1, 0, Mat(), b_hist, 1, &histSize, &histRange, uniform, accumulate);

    // 创建直方图画布
    int hist_w = 400; int hist_h = 400;
    int bin_w = cvRound((double)hist_w / histSize);

    Mat histImage(hist_w, hist_h, CV_8UC3, Scalar(0, 0, 0));

    /// 将直方图归一化到范围 [ 0, histImage.rows ]
    normalize(r_hist, r_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
    normalize(g_hist, g_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());
    normalize(b_hist, b_hist, 0, histImage.rows, NORM_MINMAX, -1, Mat());

    /// 在直方图画布上画出直方图
    for (int i = 1; i < histSize; i++)
    {
        line(histImage, Point(bin_w*(i - 1), hist_h - cvRound(r_hist.at(i - 1))),
            Point(bin_w*(i), hist_h - cvRound(r_hist.at(i))),
            Scalar(0, 0, 255), 2, 8, 0);
        line(histImage, Point(bin_w*(i - 1), hist_h - cvRound(g_hist.at(i - 1))),
            Point(bin_w*(i), hist_h - cvRound(g_hist.at(i))),
            Scalar(0, 255, 0), 2, 8, 0);
        line(histImage, Point(bin_w*(i - 1), hist_h - cvRound(b_hist.at(i - 1))),
            Point(bin_w*(i), hist_h - cvRound(b_hist.at(i))),
            Scalar(255, 0, 0), 2, 8, 0);
    }

    /// 显示直方图
    namedWindow("calcHist Demo", CV_WINDOW_AUTOSIZE);
    imshow("calcHist Demo", histImage);

    waitKey(0);

    return 0;

}