OPENCV(5) —— 图像直方图

新版本对直方图不再使用之前的histogram的形式，而是用统一的Mat或者MatND的格式来存储直方图，可见新版本Mat数据结构的优势。

#include "stdafx.h"

#include <cv.h>

#include <highgui.h>

using namespace cv;

int main( int argc, char** argv )

{

    Mat src, hsv;

    /* if( argc != 2 || !(src=imread(argv[1], 1)).data )

        return -1; */

    src=imread("zhang.jpg", 1);

    cvtColor(src, hsv, CV_BGR2HSV);

    // Quantize the hue to 30 levels

    // and the saturation to 32 levels

    int hbins = 30, sbins = 32;        // bin 步长

    int histSize[] = {hbins, sbins};

    // hue varies from 0 to 179, see cvtColor

    float hranges[] = { 0, 180 };

    // saturation varies from 0 (black-gray-white) to

    // 255 (pure spectrum color)

    float sranges[] = { 0, 256 };

    const float* ranges[] = { hranges, sranges };

    MatND hist;

    // we compute the histogram from the 0-th and 1-st channels

    int channels[] = {0, 1};   // --- hue && saturation

    calcHist( &hsv, 1, channels, Mat(), // do not use mask

        hist, 2, histSize, ranges,

        true, // the histogram is uniform

        false );

    double maxVal=0;

    minMaxLoc(hist, 0, &maxVal, 0, 0);  // Finds the global minimum and maximum in an array.

        // void minMaxLoc(InputArray src, double* minVal, double* maxVal=0, Point* minLoc=0, Point* maxLoc=0, InputArray mask=noArray())

    // 直方图显示

    int scale = 10;

    Mat histImg = Mat::zeros(sbins*scale, hbins*10, CV_8UC3);

    for( int h = 0; h < hbins; h++ )

        for( int s = 0; s < sbins; s++ )

        {

            float binVal = hist.at<float>(h, s);

            int intensity = cvRound(binVal*255/maxVal);

            rectangle( histImg, Point(h*scale, s*scale),

                Point( (h+1)*scale - 1, (s+1)*scale - 1),

                Scalar::all(intensity),    // 二维直方图，颜色之深浅代表出现个数之多寡

                CV_FILLED );

        }

        namedWindow( "Source", 1 );

        imshow( "Source", src );

        namedWindow( "H-S Histogram", 1 );

        imshow( "H-S Histogram", histImg );

        waitKey();

}