understanding ghostscript

shrink.sh

        gs                                      \
          -q -dNOPAUSE -dBATCH -dSAFER          \
          -sDEVICE=pdfwrite                     \
          -dNumRenderingThreads=2               \
          -dEmbedAllFonts=true                  \
          -dSubsetFonts=true                    \
          -dDownsampleColorImages=true          \
          -dColorImageDownsampleType=/Bicubic   \
          -dColorImageResolution=72             \
          -dDownsampleGrayImages=true           \
          -dGrayImageDownsampleType=/Bicubic    \
          -dGrayImageResolution=72              \
          -dDownsampleMonoImages=true           \
          -dMonoImageDownsampleType=/Bicubic    \
          -dMonoImageResolution=72              \
          -sOutputFile="$2"                     \
          "$1"