使用openCV画出一幅图像的直方图

// 对单通道图像做直方图
//

#include "cv.h"
#include "highgui.h"
#include <stdio.h>
#include <ctype.h>

int main( int argc, char** argv )
{
IplImage *src = 0;
IplImage *histimg = 0;
CvHistogram *hist = 0;

int hdims = 50;    // 划分HIST的个数，越高越精确
float hranges_arr[] = {0,255};
float* hranges = hranges_arr;
int bin_w;
float max_val;
int i;

if( argc != 2 || (src=cvLoadImage(argv[1], 0)) == NULL)  // force to gray image
return -1;

cvNamedWindow( "Histogram", 1 );
hist = cvCreateHist( 1, &hdims, CV_HIST_ARRAY, &hranges, 1 );  // 计算直方图
histimg = cvCreateImage( cvSize(320,200), 8, 3 );

cvZero( histimg );

cvCalcHist( &src, hist, 0, 0 ); // 计算直方图
cvGetMinMaxHistValue( hist, 0, &max_val, 0, 0 );  // 只找最大值
cvConvertScale( hist->bins, hist->bins, max_val ? 255. / max_val : 0., 0 ); // 缩放 bin 到区间 [0,255]

cvZero( histimg );
bin_w = histimg->width / hdims;  // hdims: 条的个数，则 bin_w 为条的宽度

// 画直方图
for( i = 0; i < hdims; i++ )
{
double val = ( cvGetReal1D(hist->bins,i)*histimg->height/255 );
CvScalar color = CV_RGB(255,255,0); //(hsv2rgb(i*180.f/hdims);
cvRectangle( histimg, cvPoint(i*bin_w,histimg->height),
cvPoint((i+1)*bin_w,(int)(histimg->height - val)),
color, 1, 8, 0 );
}

cvShowImage( "Histogram", histimg );
cvWaitKey(0);

cvDestroyWindow("Histogram");
cvReleaseImage( &src );
cvReleaseImage( &histimg );
cvReleaseHist ( &hist );

return 0;

}