cvSobel problems - opencv - opencv

Question

i've got the code below:
// Image Processing.cpp : Defines the entry point for the console application.
//
//Save an available image.
#include "stdafx.h"
#include "cv.h"
#include "highgui.h"
#include "cxcore.h"
/*
The purpose of this program is to show an example of THRESHOLDING.
*/
int _tmain(int argc, _TCHAR* argv[])
{
IplImage* src = cvLoadImage("D:\\document\\Study\\university of technology\\semester_8\\Computer Vision\\Pics for test\\black-white 4.jpg");
IplImage* dst = cvCreateImage(cvGetSize(src),IPL_DEPTH_8U,3);
IplImage* temp1 = cvCreateImage(cvGetSize(src),IPL_DEPTH_8U,1);
IplImage* temp2 = cvCreateImage(cvGetSize(src),IPL_DEPTH_8U,1);
cvCvtColor(src,temp1,CV_RGB2GRAY);
cvSobel(temp1,temp2,0,1,3);
cvMerge(temp2,temp2,temp2,NULL,dst);
cvNamedWindow("src",1);
cvNamedWindow("dst",1);
cvShowImage("src",src);
cvShowImage("dst",temp2);
cvWaitKey(0);
cvReleaseImage(&src);
//cvReleaseImage(&dst);
cvDestroyAllWindows();
return 0;
}
when i run it, there's an warning as the picture below:
but if i still click on "countinue" button, the result is displayed!
hope someone can give me an explaination !

Answer 1

The result is correct. The description of the program is not. Your xorder=0 and yorder=1 which means that you are detecting the first derivative in the y-direction. The white pixels in the image correspond to boundaries that can be detected by a vertical derivative, namely as close to horizontal boundaries as possible. This is why the vertical lines are barely ever detected.
CvSobel by itself has NOTHING to do with thresholding. CvSobel is a function used for finding boundaries and contours. Thresholding is most commonly an operation that creates a black-and-white image from a greyscale image. It is also called image binarization.
If you want to threshold an image, start with cvThreshold and cvAdaptiveThreshold.

Answer 2

i've fixed it, here is my code:
// Image Processing.cpp : Defines the entry point for the console application.
//
//Save an available image.
#include "stdafx.h"
#include "cv.h"
#include "highgui.h"
#include "cxcore.h"
/*
The purpose of this program is to show an example of Sobel method.
*/
int _tmain(int argc, _TCHAR* argv[])
{
IplImage* src = cvLoadImage("D:\\document\\Study\\university of technology\\semester_8\\Computer Vision\\Pics for test\\black-white 4.jpg");
IplImage* dst = cvCreateImage(cvGetSize(src),IPL_DEPTH_8U,1);
IplImage* dst_x = cvCreateImage(cvGetSize(src),IPL_DEPTH_8U,1);
IplImage* dst_y = cvCreateImage(cvGetSize(src),IPL_DEPTH_8U,1);
IplImage* temp1 = cvCreateImage(cvGetSize(src),IPL_DEPTH_8U,1);
IplImage* temp2 = cvCreateImage(cvGetSize(src),IPL_DEPTH_16S,1);
cvCvtColor(src,temp1,CV_RGB2GRAY);
cvSobel(temp1,temp2,0,1,3);
cvConvertScale(temp2,dst_y,1.0,0);
cvSobel(temp1,temp2,1,0,3);
cvConvertScale(temp2,dst_x,1.0,0);
//k nen dao ham cung luc theo x va y ma nen dao ham rieng roi dung ham cvAdd.
//cvSobel(temp1,temp2,1,1,3);
//cvConvertScale(temp2,dst,1.0,0);
cvAdd(dst_x,dst_y,dst,NULL);
cvNamedWindow("src",1);
cvNamedWindow("dst",1);
cvNamedWindow("dst_x",1);
cvNamedWindow("dst_y",1);
cvShowImage("src",src);
cvShowImage("dst",dst);
cvShowImage("dst_x",dst_x);
cvShowImage("dst_y",dst_y);
cvWaitKey(0);
cvReleaseImage(&src);
cvReleaseImage(&dst);
cvReleaseImage(&temp1);
cvReleaseImage(&temp2);
cvDestroyAllWindows();
return 0;
}