I have tried several programs which claimed to do this, but found nothing yet usable in the real world, even the ones for a single line.

Will look at Melodyne, but does it produce anything other than a score? It isn't really practicable to feed a score into a program. Needs to create it in a format such as abc, MIDI, etc.

I do remember trying a program which would scan a score with OCR and create a MIDI, but made too many scanning errors to be useful. (Amazing how much it DID recognise and convert, though)