Tony said:

>I was hoping a filter of some sort would help with the contrast by
>darkening all other colours.


   You've got the right idea. As others pointed out, optimization
   will mean matching the response of your source/detector/filter
   combination to the extent possible. Edmund Sci is the most
   accessible filter vendor in the US. Are you stuck with existing
   yellow lines, or can you paint your own? A thin line of
   retroreflective paint and a beamsplitter detection setup would
   ignore just about everything except the line you want to follow.
   Contact me off-list if you need further info.

   Reg Neale

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