[ Ref. Jerry McBride in 200608 MMDigest ]

It's a two-step process.  Scan the piano roll into a MIDI file and then
produce the notation from the MIDI file using something like Cakewalk
or Musitek SmartScore X2 Songbook.

I have found that piano rolls converted to sheet music are not very
playable because the software doesn't know where each bar begins, so
timing and note values are all over the place.  Nevertheless, with
patience, you can (almost) sort it out, or at least get some hints from
the score on embellishments to help your own playing from an original
sheet.

Geoff Ward