c++ - 无法在 OpenCV 中获取直方图图像

Question

我是 OpenCV 的新手，正在学习绘制单 channel 图像的直方图。当我运行程序时，我只得到一条白线。请告诉我这段代码有什么问题。

int histSize[1] = {256};
float hranges[2] = {0.0, 255.0};
const float* ranges[1] = {hranges};
int channels[1] = {0};

cv::MatND getHistogram(const cv::Mat &image) {
    cv::MatND hist;

    cv::calcHist(&image,1,channels,cv::Mat(),hist,1,histSize,ranges);

    return hist;
}

cv::Mat getHistogramImage(const cv::Mat &image) {
    cv::MatND hist = getHistogram(image);

    double minVal = 0;
    double maxVal = 0;

    cv::minMaxLoc(hist,&minVal,&maxVal,0,0);

    cv::Mat histImg(histSize[0],histSize[0],CV_8U,cv::Scalar(255));

    int hpt = static_cast<int>(0.9*histSize[0]);

    for(int h=0; h<256; ++h){
        float binVal = hist.at<float>(h);

        int intensity = static_cast<int>(binVal*hpt/maxVal);

        cv::line(histImg,cv::Point(h,histSize[0]),
                         cv::Point(h,histSize[0]-intensity),
                         cv::Scalar::all(0));
    }
    return histImg;
}

Answer 1

对于单 channel (以及色调 channel )，可以使用以下代码:

{
    Mat input("filepath/image.jpg", 1);
    Mat hsv_input;

cvtColor( input, hsv_input, CV_BGR2HSV );

int h_bins = 5; 
int histSize[] = { h_bins}; 
float h_ranges[] = { 0, 180 };

const float* ranges[] = { h_ranges};
int channels[] = { 0 };

MatND original_hist_input;
calcHist( &hsv_input, 1, channels, Mat(), original_hist_input, 1, histSize, ranges, true, false );
normalize( original_hist_input, original_hist_input, 0, 1, NORM_MINMAX, -1, Mat() );    

}