problem regarding edge detection

I am applying edge detection methods like Sobel, prewitt,robert etc. Can anybody please tell me how can I find probability of detection & Probability of False alarm with different values of SNR, after applying these edge detection methods... Thanks in advance..

Answer 1

[Image Analyst]

Call bwlabel to label the images. Then use something like ginput to ask your user which edges are genuine and which are false. Then just take the ratio of the number of false blobs divided by the total number of blobs.

[matlab_image]

Thanks for your answer. But can you please explain it a little bit more. Is there any method of finding Probability of Detection(PD) and Probability of False Alarm(PFA) without taking input from user i.e. is there any possible method for finding PD & PFA. I have another question to ask from you. When I am using ginput without giving any n value, I don't know how to stop it.In the matlab help it is written that "[x,y] = ginput gathers an unlimited number of points until you press the Return key." Can you please tell me which is Return key????? Thanks in advance......

[Walter Roberson]

Whether something is considered an edge or not can depend upon intention. For example, you might have an image of fabric that has a strong paisley pattern (a pattern that has strong visual edges), and yet be interested in detecting the seams that have little visual presence, by careful analysis of mis-alignment in blobs.

Or my favorite example: the Cosmic Microwave Background Radiation (CMBR) was considered pure noise when it was originally noticed, but later it became important to re-examine those images masking out the more obvious structures to find the subtle ones.

It is therefore not possible to construct a program which finds the PD and PFA without taking input from the user about what the features of interest are.

[matlab_image]

ok..thanks. can you please give me answer of my 2nd question.When I am using ginput without giving any n value, I don't know how to stop it.In the matlab help it is written that "[x,y] = ginput gathers an unlimited number of points until you press the Return key." Can you please tell me which is Return key?????

[Walter Roberson]

Some keyboards label the Return key with the label "Return". Some keyboards label it with the label "Enter". Some label it "Entre'". Others probably label it other things. It is usually an oversized key near the right-hand side of the main keyboard.

[matlab_image]

Thanks a lot......I have 3 questions to ask from you: 1)Can any of you please explain it a little bit more.I am still unable to calculate the value of PD and PFA... Please help me I need it very urgent.... I have applied bwlabel and ginput but after this how to calculate the ratio of false blobs and total blobs.................. 2)when I click on false edges how can i know how many times user clicked for false edge..Is it taken manually or is there any method for counting no. of clicks...............3)I have another problem which is not related with this is that I am facing lots of problems while logging into and opening Mathworks. Can you please tell me what is the reason behind this...

[Image Analyst]

1) If you don't know if an edge is a true edge or a false edge then I can't help you. Perhaps you can just make up random numbers in that case. I mean, if you don't know what's true and false then who would?

2) numberOfClicks = length(x); where x is returned from ginput().

3) Call the Mathworks and tell them that you can't use their web site because of some kind of a login problem.

[matlab_image]

Thanks for answering..... I know which are false edges and which are true.. but I have doubts about PD and PFA..... So I will try to clear these while reading some tutorials........ Thanks again....