边缘梯度方向直方图的构建

在手势识别时,可利用模板手势与当前手势的边缘梯度方向直方图进行匹配来识别当前手势, 故而就需要构建图像的边缘梯度方向直方图.

梯度为：dx*dx+dy*dy开方.  　　　　　　　　　　

梯度方向则为：dy/dx(注意dx为0的情况处理).

#include "stdafx.h"
#include "cv.h"
#include "highgui.h"

int main()
{
    IplImage* src=cvLoadImage("C:/Users/shark/Desktop/fruits.jpg",0);
    CvSize size=cvGetSize(src);
    //边缘检测
    IplImage* canny=cvCreateImage(size,8,1);
    IplImage* canny32=cvCreateImage(size,IPL_DEPTH_32F,1);
    cvCanny(src,canny,60,180,3);
    cvConvert(canny,canny32);
    //梯度计算
    IplImage* dx=cvCreateImage(size,IPL_DEPTH_16S,1);
    IplImage* dy=cvCreateImage(size,IPL_DEPTH_16S,1);
    cvSobel(src,dx,1,0,3);
    cvSobel(src,dy,0,1,3);
    IplImage* dx32=cvCreateImage(size,IPL_DEPTH_32F,1);
    IplImage* dy32=cvCreateImage(size,IPL_DEPTH_32F,1);
    cvConvert(dx,dx32);
    cvConvert(dy,dy32);
    IplImage* gradient=cvCreateImage(size,IPL_DEPTH_32F,1);       //梯度图像
    IplImage* gradient_dir=cvCreateImage(size,IPL_DEPTH_32F,1);   //梯度方向图像
    cvDiv(dx32,dy32,gradient_dir);
　　
    cvMul(dx32,dx32,dx32,1.0);
    cvMul(dy32,dy32,dy32,1.0);
    cvAdd(dx32,dy32,gradient,0);
    for(int i=0;i<size.height;i++)
        for(int j=0;j<size.width;j++)
        {
            gradient->imageData[i*gradient->widthStep+j]=cvSqrt((float)

                gradient->imageData[i*gradient->widthStep+j]);
        }
    　　float theta;
        for(int i=0;i<size.height;i++)
            for(int j=0;j<size.width;j++)
            {
                if(cvGetReal2D(canny32,i,j)!=0 && cvGetReal2D(dx32,i,j)!=0)    

                    //dy/dx中dx!=0
                {
                    theta=cvGetReal2D(gradient_dir,i,j);
                    theta=atan(theta);
                    cvSetReal2D(gradient_dir,i,j,theta);
                }
                else
                {
                    cvSetReal2D(gradient_dir,i,j,0);
                }
            }
            int bins=20; float max=0;
            float range[]={-CV_PI/2,CV_PI/2};
            float* ranges[]={range};
            CvHistogram* hist=cvCreateHist(1,&bins,CV_HIST_ARRAY,ranges,1);
            IplImage* hist_img=cvCreateImage(cvSize(320,200),8,3);
            cvZero(hist_img);
            cvCalcHist(&gradient_dir,hist,0,canny);                       //只计算边界直方图
            cvGetMinMaxHistValue(hist,0,&max,0,0);
            cvConvertScale(hist->bins,hist->bins,max?255./max:0.,0);   //缩放bin到[0，255]
            double bin_width=(double)hist_img->width/bins*3/4;
            for(int i=0;i<bins;i++)
            {
                double val=cvGetReal1D(hist->bins,i)*hist_img->height/255;
                CvPoint p0=cvPoint(30+i*bin_width,hist_img->height);
                CvPoint p1=cvPoint(30+(i+1)*bin_width,hist_img->height-val);
                cvRectangle(hist_img,p0,p1,cvScalar(0,255),1,8,0);
            }
            cvNamedWindow("hist_img");
            cvShowImage("hist_img",hist_img);
            cvWaitKey();


}

原图：

梯度方向直方图：