pngtopnm map600.png | pnmcut -left 300 -top 300 -width 20400 -height 13200 > map600.ppm
cat map600.ppm | pnmdepth 65535 | pnmgamma -srgbramp -ungamma | pnmscale -reduce 4 | pnmgamma -srgbramp | pnmdepth 255 > map150.ppm
cat map600.ppm | pnmdepth 65535 | pnmgamma -srgbramp -ungamma | pnmscale -reduce 8 | pnmgamma -srgbramp | pnmdepth 255 > map75.ppm
cat overlay_2p_600.ppm | pnmdepth 65535 | pnmgamma -srgbramp -ungamma | pnmscale -reduce 4 | pnmgamma -srgbramp | pnmdepth 255 > overlay_2p_150.ppm
cat overlay_2p_600.ppm | pnmdepth 65535 | pnmgamma -srgbramp -ungamma | pnmscale -reduce 8 | pnmgamma -srgbramp | pnmdepth 255 > overlay_2p_75.ppm
cat overlay_3p_600.ppm | pnmdepth 65535 | pnmgamma -srgbramp -ungamma | pnmscale -reduce 4 | pnmgamma -srgbramp | pnmdepth 255 > overlay_3p_150.ppm
cat overlay_3p_600.ppm | pnmdepth 65535 | pnmgamma -srgbramp -ungamma | pnmscale -reduce 8 | pnmgamma -srgbramp | pnmdepth 255 > overlay_3p_75.ppm