Re: CvSobel

Hello Luiz,
Still I get wrong results
For example I have an Image:
0 0 0 0 0 0 0 0 0 0
0 1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19
20 21 22 23 24 25 26 27 28 29
30 31 32 33 34 35 36 37 38 39
40 41 42 43 44 45 46 47 48 49
50 51 52 53 54 55 56 57 58 59
60 61 62 63 64 65 66 67 68 69
70 71 72 73 74 75 76 77 78 79
80 81 82 83 84 85 86 87 88 89

If I run following code...

IplImage* derivx = cvCreateImage(cvSize(width,height),IPL_DEPTH_16S,1);
IplImage* scaledderivx = cvCreateImage(cvSize(width,height),IPL_DEPTH_8U,1);
cvSobel(image2,derivx,1,0);
cvConvert(derivx,scaledderivx);

...., I get following Sobel matrix:
1 2 2 2 2 2 2 2 2 1
0 0 3 6 6 6 6 6 6 6
6 3 0 0 4 8 8 8 8 8
8 8 8 4 0 0 4 8 8 8
8 8 8 8 8 4 0 0 4 8
8 8 8 8 8 8 8 4 0 0
4 8 8 8 8 8 8 8 8 4
0 0 4 8 8 8 8 8 8 8
8 4 0 0 4 8 8 -91 0 0
0 -9 19 0 0 0 0 0 0 -1


But this are wrong values! If I manually compute the first derivate with 
filter [-1 0 1], the value of Pixel (2,2) for example is "13*1 + 12*0 -11" = 
2 and not 0 as computed by cvSobel.

What is wrong here?


Thank you very much

Stefan


















Am Dienstag, 7. März 2006 15:22 schrieb Luiz Curado:
>   Hello, Stefan!
>
>   Try something like this:
>
>   IplImage* src;
>   IplImage* outra;
>   IplImage* sobelImg;
>
>   // load src
>   outra = cvCreateImage( cvGetSize(src), IPL_DEPTH_16S, 1 );
>   cvSobel( src, outra, 1, 1 );
>   sobelImg = cvCreateImage( cvGetSize(src), IPL_DEPTH_8U, 1 );
>   cvConvertScale( outra, sobelImg );
>   cvNamedWindow( "3.Sobel", 1 );
>   cvShowImage( "3.Sobel", sobelImg );
>
>   With best regards,
>
>   Luiz Reginaldo
>
>
> Stefan Meyer <stefan.meyer@xxxxxxxxxxxxxxxxxxxxxxxxxx> escreveu:
>   Hello,
> could anyone explain me the usage of CVSobel? I Dont know, how I can
> compute the first derivatives respectively how I can use the result of
> CVSobel. If I compute the derivative manually, I get other values.
>
> Thanks
> Stefan
>
>
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-- 
Stefan Meyer
Phone: +49 9131 85-25158
Fax: +49 9131 85-25149

University of Erlangen-Nuremberg
 Department of Computer Science 12
 (Hardware-Software-Co-Design)
 Am Weichselgarten 3
 D-91058 Erlangen
 Germany


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