<DIV>Hi Bill,</DIV> <DIV>Sure, my mistake I meant variance of 30 (ITK) and standard deviation of 5 (MATLAB) which is very close. Can anyone help me with my other questions?</DIV> <DIV> </DIV> <DIV>Thank you very much,</DIV> <DIV>Shlomo.<BR><BR><B><I>Bill Lorensen <bill.lorensen@gmail.com></I></B> wrote:</DIV> <BLOCKQUOTE class=replbq style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #1010ff 2px solid">The CannyEdgeDetectionImageFilter has a SetVariance method. The variance is sigma squared. Are you specifying a variance of 900?<BR><BR>Bill<BR><BR><BR> <DIV><SPAN class=gmail_quote>On 6/25/06, <B class=gmail_sendername>Shlomo Kashani.</B> <<A href="mailto:shlomo_kashani@yahoo.com">shlomo_kashani@yahoo.com</A>> wrote:</SPAN> <BLOCKQUOTE class=gmail_quote style="PADDING-LEFT: 1ex; MARGIN: 0pt 0pt 0pt 0.8ex; BORDER-LEFT: rgb(204,204,204) 1px solid"> <DIV><SPAN class=e id=q_10c0bc21b3e323ce_0> <DIV style="MARGIN: 0in 0in 0pt"><FONT
face="Times New Roman" size=3>Hi All,</FONT></DIV> <DIV style="MARGIN: 0in 0in 0pt"><FONT face="Times New Roman" size=3>I am trying to use the class </FONT><SPAN style="FONT-SIZE: 10pt">CannyEdgeDetectionImageFilter </SPAN><FONT face="Times New Roman" size=3>in an iris recognition system. One of the first steps is segmenting the iris and the pupil by and edge detector and then finding the radii of the pupil and the iris using a circular Hough Transform. I have several questions regarding the canny edge detector implementation in ITK:</FONT></DIV> <DIV style="MARGIN: 0in 0in 0pt"><FONT face="Times New Roman" size=3></FONT> </DIV> <DIV style="MARGIN: 0in 0in 0pt"><FONT face="Times New Roman" size=3>1-I understand that in the original paper by Canny a first derivative of a Gaussian was used while ITK uses a LoG operator (second derivative of a Gaussian). Why was this method chosen over the original suggested method? </FONT></DIV> <DIV style="MARGIN: 0in 0in
0pt"><FONT face="Times New Roman" size=3></FONT> </DIV> <DIV style="MARGIN: 0in 0in 0pt"><FONT face="Times New Roman" size=3>2-in the class </FONT><SPAN style="FONT-SIZE: 10pt">CannyEdgeDetectionImageFilter</SPAN><FONT face="Times New Roman" size=3>, I noticed that there is no way of specifying the SIZE of the Gaussian kernel that the canny edge detector would use (by a call to </FONT><SPAN style="FONT-SIZE: 10pt">DiscreteGaussianImageFilter I guess ???)</SPAN><FONT face="Times New Roman" size=3>, rather only the standard deviation can be specified and I understand that the kernel size is determined automatically from the standard deviation. Is that correct and is there a way to over ride this behavior?</FONT></DIV> <DIV style="MARGIN: 0in 0in 0pt"><FONT face="Times New Roman" size=3></FONT> </DIV> <DIV style="MARGIN: 0in 0in 0pt"><FONT face="Times New Roman" size=3>3-I noticed that when using ITK I have to use a standard deviation as large as *30* which would
probably result in a huge Gaussian and Gaussian derivative kernel size while when using MATLAB (which uses a first derivative of a Gaussian) a standard deviation of 5 is enough. How come there is such a hug difference?</FONT></DIV> <DIV style="MARGIN: 0in 0in 0pt"><FONT face="Times New Roman" size=3></FONT> </DIV> <DIV style="MARGIN: 0in 0in 0pt"><FONT face="Times New Roman" size=3>Any help would be appreciated, </FONT></DIV> <DIV style="MARGIN: 0in 0in 0pt"><FONT face="Times New Roman" size=3></FONT> </DIV> <DIV style="MARGIN: 0in 0in 0pt"><FONT size=3><FONT face="Times New Roman">Shlomo Kashani. <SPAN> </SPAN></FONT></FONT> </DIV></SPAN></DIV> <DIV><SPAN class=ad> <DIV></DIV> <HR SIZE=1> Yahoo! Messenger with Voice. <A onclick="return top.js.OpenExtLink(window,event,this)" href="http://us.rd.yahoo.com/mail_us/taglines/postman1/*http://us.rd.yahoo.com/evt=39663/*http://voice.yahoo.com" target=_blank>Make PC-to-Phone Calls</A> to the US (and 30+
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