Convert NEF to PNG Images

Refer: https://superuser.com/questions/577643/how-do-i-batch-convert-thousands-of-nefs-to-jpegs

Install Applications

sudo apt-get install netpbm dcraw

Convert One Image

dcraw -c -w input.NEF | pnmtopng > output.png

Run Application Against Multiple Files

for filename in *.NEF ; do dcraw -c -w "$filename" | pnmtopng > "$filename.png" ; done