Understanding the Pattern-Matching algorithm

[pellman]

I have a user that decided to look for a pattern that is a quarter of the size of the image in a basically grey image with some very small contrast differences in the pattern. This was done to verify consistency (I'm not sure it is a valid test). Most of the time the pattern is found with a score that varies with the noice in the image, with sccores around 500 to 800. Now and then the search fails completly with no score. My question is: Will the algorithm used sometimes fail due to that it finds so many matches that a good decision can't be generated or is there some other explanaition on this case.

[Sean_C.]

Hello Pellman,

Thank you for contacting National Instruments.

What hardware and software are you using? If LabVIEW, what version? It would also be helpful if you could post your pattern matching algorithm.

Please respond with more information and I will be glad to help.

Sean C.
Applications Engineer
National Instruments

[pellman]

Sean

I'm using NI 1409 Frame grabber with LabView 6.1 and Vision 6.1 Pattern matching Vi's using the "IMAQ Setup Match Pattern.Vi and IMAQ Match Pattern that uses LV_MatchPattern.
So the Algorithm is NI's.

I'm trying to figure out the reason that it sometimes can't find the pattern at all. As mentioned the Image is basically a grey image with very little contrast and has a faint pattern in it but is relatively noisy.

Basically an explanation on what can happen in the algorithm that causes this failure. As mentioned in my first message , I don't think this is a valid test that my customer is doing so I would like to have a good explanation why it is not good.

[Julie S]

Most likely the failure is due to the fact that the pattern is faint and there is a lot of noise which blurs the pattern even more. For more detailed information on the Pattern Matching algorithm, take a look at the following resources.

How to Match Patterns or Shapes in IMAQ Vision?
http://digital.ni.com/public.nsf/websearch/862567530005F09C86256754005ED3D8

IMAQ Vision for LabVIEW User Manual, page 5-17:
http://digital.ni.com/manuals.nsf/websearch/CDEE235576535B2586256D3C005FBC98?OpenDocument&node=132090_US

IMAQ Vision Concepts Manual, chapter 12
http://digital.ni.com/manuals.nsf/websearch/55A90080787F932586256D3C0065F4DA?OpenDocument&node=132090_US

Hope this helps -
Julie S
Applications Engineer
National Instruments