solution for pixel radiance problem

Hi Greg,
  Thanks for telling me the options "-ps 1 -pj 0 -dt 0 -sj 0", it
indeed increase the accuracy. But the error is still very large. Again
thanks for telling me the command "rtrace". It's really a useful tool to
help me debug my program and it facilitated me to find out there is
something wrong about conversion from PIC file to TIFF file. I failed to
disable the gamma correction!!! After setting the gamma exponent to 1, all
the values are correct. Many many thanks!!!