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
