学习OpenCV——绘制彩色直方图（HSV2BGR）

#include <cv.h>
#include <highgui.h>
#include <iostream>
using namespace std;

int main( int argc, char** argv )
{
    IplImage * src= cvLoadImage("D:/2.jpg");

    IplImage* hsv = cvCreateImage( cvGetSize(src), 8, 3 );
    IplImage* h_plane = cvCreateImage( cvGetSize(src), 8, 1 );
    IplImage* s_plane = cvCreateImage( cvGetSize(src), 8, 1 );
    IplImage* v_plane = cvCreateImage( cvGetSize(src), 8, 1 );
    IplImage* planes[] = { h_plane, s_plane };

    /** H 分量划分为16个等级，S分量划分为8个等级 */
    int h_bins = 16, s_bins = 8;
    int hist_size[] = {h_bins, s_bins};

    /** H 分量的变化范围 */
    float h_ranges[] = { 0, 180 }; 

    /** S 分量的变化范围*/
    float s_ranges[] = { 0, 255 };
    float* ranges[] = { h_ranges, s_ranges };

    /** 输入图像转换到HSV颜色空间 */
    cvCvtColor( src, hsv, CV_BGR2HSV );
    cvCvtPixToPlane( hsv, h_plane, s_plane, v_plane, 0 );

    /** 创建直方图，二维, 每个维度上均分 */
    CvHistogram * hist = cvCreateHist( 2, hist_size, CV_HIST_ARRAY, ranges, 1 );
    /** 根据H,S两个平面数据统计直方图 */
    cvCalcHist( planes, hist, 0, 0 );

    /** 获取直方图统计的最大值，用于动态显示直方图 */
    float max_value;
    cvGetMinMaxHistValue( hist, 0, &max_value, 0, 0 );

    /** 设置直方图显示图像 */
    int height = 240;
    int width = (h_bins*s_bins*6);
    IplImage* hist_img = cvCreateImage( cvSize(width,height), 8, 3 );
    cvZero( hist_img );

    /** 用来进行HSV到RGB颜色转换的临时单位图像 */
    IplImage * hsv_color = cvCreateImage(cvSize(1,1),8,3);
    IplImage * rgb_color = cvCreateImage(cvSize(1,1),8,3);
    int bin_w = width / (h_bins * s_bins);
    for(int h = 0; h < h_bins; h++)
    {
        for(int s = 0; s < s_bins; s++)
        {
            int i = h*s_bins + s;
            /** 获得直方图中的统计次数，计算显示在图像中的高度 */
            float bin_val = cvQueryHistValue_2D( hist, h, s );
            int intensity = cvRound(bin_val*height/max_value);//Round, Floor, Ceil 转换浮点数为整数（cvRound 返回和参数最接近的整数值。 cvFloor 返回不大于参数的最大整数值。cvCeil 返回不小于参数的最小整数值。）

            /** 获得当前直方图代表的颜色，转换成RGB用于绘制 */
            cvSet2D(hsv_color,0,0,cvScalar(h*180.f / h_bins,s*255.f/s_bins,255,0));
            cvCvtColor(hsv_color,rgb_color,CV_HSV2BGR);
            CvScalar color = cvGet2D(rgb_color,0,0);

            cvRectangle( hist_img, cvPoint(i*bin_w,height),
                cvPoint((i+1)*bin_w,height - intensity),
                color, -1, 8, 0 );
        }
    }

    cvNamedWindow( "Source", 1 );
    cvShowImage( "Source", src );

    cvNamedWindow( "H-S Histogram", 1 );
    cvShowImage( "H-S Histogram", hist_img );

    cvWaitKey(0);
}

from： http://blog.csdn.net/yangtrees/article/details/7433598