Optical music recognition (OMR) or Music OCR is the application of optical character recognition to interpret sheet music or printed scores into editable or playable form. Once captured digitally, the music can be saved in commonly used file formats, e.g. MIDI (for playback) and MusicXML (for page layout).
Early research into recognition of printed sheet music was performed at the graduate level in the late 1960s at MIT and other institutions. Successive efforts were made to localize and remove musical staff lines leaving symbols to be recognized and parsed. The first commercial music-scanning product, MIDISCAN (now SmartScore), was released in 1991 by Musitek corporation.
Unlike OCR of text, where words are parsed sequentially, music notation involves parallel elements, as when several voices are present along with unattached performance symbols positioned nearby. Therefore, the spatial relationship between notes, expression marks, dynamics, articulations and other annotations is an important part of the expression of the music.
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PDFtoMUSIC by Myriad is often seen as a Music OCR software, but it does actually no optical character recognition. The program simply reads PDF files which have been created by some scorewriter, locates the musical glyphs which have been written directly as characters of a music notation font. The optical recognition consists of concluding the musical relationship of those glyphs from their relative position in space, i.e. on the logical page of the PDF document, and combine those to a musical score. Only the PRO version can export this to a MusicXML file, while the standard version works only for the scorewriters by Myriad.