学步园

下面用两种方法实现直方图的计算和绘制，其一用自己实现计算直方图，其二利用OpenCV提供的库函数计算直方图。代码和算法不难，适合OpenCV初学者学习之用。如有疏漏错误之处，还请各路方家指出。下面使用的测试图是标准的lena图。

代码之一

#include <cv.h><br /> #include <highgui.h><br /> #pragma comment( lib, "cv.lib" )<br /> #pragma comment( lib, "cxcore.lib" )<br /> #pragma comment( lib, "highgui.lib" )<br /> int main()<br /> {<br /> IplImage* src=cvLoadImage("lena.jpg",0);<br /> int width=src->width;<br /> int height=src->height;<br /> int step=src->widthStep;<br /> uchar* data=(uchar *)src->imageData;<br /> int hist[256]={0};<br /> for(int i=0;i<height;i++)<br /> {<br /> for(int j=0;j<width;j++)<br /> {<br /> hist[data[i*step+j]]++;<br /> }<br /> }<br /> int max=0;<br /> for(i=0;i<256;i++)<br /> {<br /> if(hist[i]>max)<br /> {<br /> max=hist[i];<br /> }<br /> }<br /> IplImage* dst=cvCreateImage(cvSize(400,300),8,3);<br /> cvSet(dst,cvScalarAll(255),0);<br /> double bin_width=(double)dst->width/256;<br /> double bin_unith=(double)dst->height/max;<br /> for(i=0;i<256;i++)<br /> {<br /> CvPoint p0=cvPoint(i*bin_width,dst->height);<br /> CvPoint p1=cvPoint((i+1)*bin_width,dst->height-hist[i]*bin_unith);<br /> cvRectangle(dst,p0,p1,cvScalar(0,255),-1,8,0);<br /> }<br /> cvNamedWindow("src",1);<br /> cvShowImage("src",src);<br /> cvNamedWindow("dst",1);<br /> cvShowImage("dst",dst);<br /> cvWaitKey(0);<br /> cvDestroyAllWindows();<br /> cvReleaseImage(&src);<br /> cvReleaseImage(&dst);<br /> return 0;<br /> }

代码效果如下

代码之二

#include <cv.h><br /> #include <highgui.h><br /> #pragma comment( lib, "cv.lib" )<br /> #pragma comment( lib, "cxcore.lib" )<br /> #pragma comment( lib, "highgui.lib" )<br /> int main()<br /> {<br /> IplImage* src=cvLoadImage("lena.jpg",0);<br /> int size=256;<br /> float range[]={0,255};<br /> float* ranges[]={range};<br /> CvHistogram* hist=cvCreateHist(1,&size,CV_HIST_ARRAY,ranges,1);<br /> cvCalcHist(&src,hist,0,NULL);<br /> float max=0;<br /> cvGetMinMaxHistValue(hist,NULL,&max,NULL,NULL);<br /> IplImage* dst=cvCreateImage(cvSize(400,300),8,3);<br /> cvSet(dst,cvScalarAll(255),0);<br /> double bin_width=(double)dst->width/size;<br /> double bin_unith=(double)dst->height/max;<br /> for(int i=0;i<size;i++)<br /> {<br /> CvPoint p0=cvPoint(i*bin_width,dst->height);<br /> CvPoint p1=cvPoint((i+1)*bin_width,dst->height-cvGetReal1D(hist->bins,i)*bin_unith);<br /> cvRectangle(dst,p0,p1,cvScalar(0,255),-1,8,0);<br /> }<br /> cvNamedWindow("src",1);<br /> cvShowImage("src",src);<br /> cvNamedWindow("dst",1);<br /> cvShowImage("dst",dst);<br /> cvWaitKey(0);<br /> cvDestroyAllWindows();<br /> cvReleaseImage(&src);<br /> cvReleaseImage(&dst);<br /> return 0;<br /> }

代码效果如下

可见上面两种方法的结果并无明显的差异。

通过复用上面的代码。我们可以得到彩色图像各通道的直方图，代码如下

#include <cv.h><br /> #include <highgui.h><br /> #pragma comment( lib, "cv.lib" )<br /> #pragma comment( lib, "cxcore.lib" )<br /> #pragma comment( lib, "highgui.lib" )<br /> int main()<br /> {<br /> IplImage* src=cvLoadImage("lena.jpg",1);<br /> IplImage* r=cvCreateImage(cvGetSize(src), IPL_DEPTH_8U, 1);<br /> IplImage* g=cvCreateImage(cvGetSize(src), IPL_DEPTH_8U, 1);<br /> IplImage* b=cvCreateImage(cvGetSize(src), IPL_DEPTH_8U, 1);<br /> cvSplit(src,b,g,r,NULL);<br /> IplImage* gray = cvCreateImage(cvGetSize(src),8,1);<br /> cvCvtColor(src,gray,CV_BGR2GRAY);<br /> int size=256;<br /> float range[]={0,255};<br /> float* ranges[]={range};</p> <p> CvHistogram* r_hist = cvCreateHist(1,&size,CV_HIST_ARRAY,ranges,1);<br /> CvHistogram* g_hist = cvCreateHist(1,&size,CV_HIST_ARRAY,ranges,1);<br /> CvHistogram* b_hist = cvCreateHist(1,&size,CV_HIST_ARRAY,ranges,1);<br /> CvHistogram* hist = cvCreateHist(1,&size,CV_HIST_ARRAY,ranges,1);<br /> cvCalcHist(&r,r_hist,0,NULL);<br /> IplImage* r_dst=cvCreateImage(cvSize(400,300),8,3);<br /> cvSet(r_dst,cvScalarAll(255),0);<br /> float r_max=0;<br /> cvGetMinMaxHistValue(r_hist,NULL,&r_max,NULL,NULL);<br /> double r_bin_width=(double)r_dst->width/size;<br /> double r_bin_unith=(double)r_dst->height/r_max;<br /> for(int i=0;i<size;i++)<br /> {<br /> CvPoint p0=cvPoint(i*r_bin_width,r_dst->height);<br /> CvPoint p1=cvPoint((i+1)*r_bin_width,r_dst->height-cvGetReal1D(r_hist->bins,i)*r_bin_unith);<br /> cvRectangle(r_dst,p0,p1,cvScalar(255,0,0),-1,8,0);<br /> }<br /> cvCalcHist(&g,g_hist,0,NULL);<br /> IplImage* g_dst=cvCreateImage(cvSize(400,300),8,3);<br /> cvSet(g_dst,cvScalarAll(255),0);<br /> float g_max=0;<br /> cvGetMinMaxHistValue(g_hist,NULL,&g_max,NULL,NULL);<br /> double g_bin_width=(double)g_dst->width/size;<br /> double g_bin_unith=(double)g_dst->height/g_max;<br /> for(i=0;i<size;i++)<br /> {<br /> CvPoint p0=cvPoint(i*g_bin_width,g_dst->height);<br /> CvPoint p1=cvPoint((i+1)*g_bin_width,g_dst->height-cvGetReal1D(g_hist->bins,i)*g_bin_unith);<br /> cvRectangle(g_dst,p0,p1,cvScalar(0,255,0),-1,8,0);<br /> }<br /> cvCalcHist(&b,b_hist,0,NULL);<br /> IplImage* b_dst=cvCreateImage(cvSize(400,300),8,3);<br /> cvSet(b_dst,cvScalarAll(255),0);<br /> float b_max=0;<br /> cvGetMinMaxHistValue(b_hist,NULL,&b_max,NULL,NULL);<br /> double b_bin_width=(double)b_dst->width/size;<br /> double b_bin_unith=(double)b_dst->height/b_max;<br /> for(i=0;i<size;i++)<br /> {<br /> CvPoint p0=cvPoint(i*b_bin_width,b_dst->height);<br /> CvPoint p1=cvPoint((i+1)*b_bin_width,b_dst->height-cvGetReal1D(b_hist->bins,i)*b_bin_unith);<br /> cvRectangle(b_dst,p0,p1,cvScalar(0,0,255),-1,8,0);<br /> }<br /> cvCalcHist(&gray,hist,0,NULL);<br /> IplImage* gray_dst=cvCreateImage(cvSize(400,300),8,3);<br /> cvSet(gray_dst,cvScalarAll(255),0);<br /> float max=0;<br /> cvGetMinMaxHistValue(hist,NULL,&max,NULL,NULL);<br /> double bin_width=(double)gray_dst->width/size;<br /> double bin_unith=(double)gray_dst->height/max;<br /> for(i=0;i<size;i++)<br /> {<br /> CvPoint p0=cvPoint(i*bin_width,gray_dst->height);<br /> CvPoint p1=cvPoint((i+1)*bin_width,gray_dst->height-cvGetReal1D(hist->bins,i)*bin_unith);<br /> cvRectangle(gray_dst,p0,p1,cvScalar(0),-1,8,0);<br /> }<br /> IplImage* dst=cvCreateImage(cvSize(800,600),8,3);<br /> cvSetZero(dst);<br /> CvRect rect = cvRect(0, 0, 400, 300);<br /> cvSetImageROI(dst, rect);<br /> cvCopy(r_dst, dst);<br /> rect = cvRect(400, 0, 400, 300);<br /> cvSetImageROI(dst, rect);<br /> cvCopy(g_dst, dst);<br /> rect = cvRect(0, 300, 400, 300);<br /> cvSetImageROI(dst, rect);<br /> cvCopy(b_dst, dst);<br /> rect = cvRect(400, 300, 400, 300);<br /> cvSetImageROI(dst, rect);<br /> cvCopy(gray_dst, dst);<br /> cvResetImageROI(dst);<br /> cvNamedWindow("src",1);<br /> cvShowImage("src",src);<br /> cvNamedWindow("dst",1);<br /> cvShowImage("dst",dst);<br /> cvSaveImage("dst.jpg",dst);<br /> cvWaitKey(0);<br /> cvDestroyAllWindows();<br /> cvReleaseImage(&src);<br /> cvReleaseImage(&dst);<br /> cvReleaseImage(&r);<br /> cvReleaseImage(&g);<br /> cvReleaseImage(&b);<br /> cvReleaseImage(&gray);<br /> cvReleaseImage(&r_dst);<br /> cvReleaseImage(&g_dst);<br /> cvReleaseImage(&b_dst);<br /> cvReleaseImage(&gray_dst);<br /> return 0;<br /> }

效果图如下