导数 sobel
核心函数：cvSobel
程序：
第5个参数使用CV_SCHARR对于第二个原图像的效果：
代码：
#include "cv.h"
#include "cxcore.h"
#include "highgui.h"
#include <iostream>
int DerivativeSobel(int argc,char** argv)
{
IplImage* src=cvLoadImage("e:\\picture\\7.JPG",0);
IplImage* dst1=cvCreateImage(cvGetSize(src),IPL_DEPTH_16S,src->nChannels); //注意类型是IPL_DEPTH_16S
IplImage* x1=cvCreateImage(cvGetSize(src),8,src->nChannels);
IplImage* x2=cvCreateImage(cvGetSize(src),8,src->nChannels);
IplImage* y1=cvCreateImage(cvGetSize(src),8,src->nChannels);
IplImage* y2=cvCreateImage(cvGetSize(src),8,src->nChannels);
IplImage* x1y1=cvCreateImage(cvGetSize(src),8,src->nChannels);
IplImage* x2y2=cvCreateImage(cvGetSize(src),8,src->nChannels);
cvZero(dst1);
cvSobel(src,dst1,1,0,3); //对x求1阶导
cvConvertScale(dst1,x1);
cvZero(dst1);
cvSobel(src,dst1,2,0,3); //对x求2阶导
cvConvertScale(dst1,x2);
cvZero(dst1);
cvSobel(src,dst1,0,1,3); //对y求1阶导
cvConvertScale(dst1,y1);
cvZero(dst1);
cvSobel(src,dst1,0,2,3); //对y求2阶导
cvConvertScale(dst1,y2);
cvZero(dst1);
cvSobel(src,dst1,1,1,3); //对x和y求1阶导
cvConvertScale(dst1,x1y1);
cvZero(dst1);
cvSobel(src,dst1,2,2,3); //对x和y求2阶导
cvConvertScale(dst1,x2y2);
cvNamedWindow("src");
cvNamedWindow("x1");
cvNamedWindow("x2");
cvNamedWindow("y1");
cvNamedWindow("y2");
cvNamedWindow("x1y1");
cvNamedWindow("x2y2");
cvShowImage("src",src);
cvShowImage("x1",x1);
cvShowImage("x2",x2);
cvShowImage("y1",y1);
cvShowImage("y2",y2);
cvShowImage("x1y1",x1y1);
cvShowImage("x2y2",x2y2);
cvWaitKey(0);
cvDestroyWindow("src");
cvDestroyWindow("x1");
cvDestroyWindow("x2");
cvDestroyWindow("y1");
cvDestroyWindow("y2");
cvDestroyWindow("x1y1");
cvDestroyWindow("x2y2");
cvReleaseImage(&src);
cvReleaseImage(&dst1);
cvReleaseImage(&x1);
cvReleaseImage(&x2);
cvReleaseImage(&y1);
cvReleaseImage(&y2);
cvReleaseImage(&x1y1);
cvReleaseImage(&x2y2);
return 0;
}
总结：
对x方向的1阶导数是沿着X轴方向的变化程度，对Y方向的1阶导数是沿着Y轴方向的变化程度
1阶导数从低值变化到高值为正，所以可以显示出来白色，而反过来为负，所以显示不出来了，而二阶导数却都为正数，所以都能显示；因此一阶导数常常只能显示内轮廓或者外轮廓（是哪个具体看哪个是从低值到高值），而二阶导数能够同时显示内轮廓和外轮廓
对x和y同时求一阶导数只能x和y方向都有变化的才能显示出来，否则不显示，二阶导数同理