What kind of filtering areyou doing? Are you using IPP?
An image of size640x480 is so small that it is hard tobelieve inany performance gains from switching to
more thanone thread to process it. Don't forget aboutcontext switches of threads becausethey don't
I woulduse a different technique to increase a performance of processing, that is,a priority boostto high
for a thread that does image processing.
You need to usevTune to analyze why the slowdown happens.