About accid and accid.ges

[rigaux]

When running musicdiff to compare a MEI predicted score (obtained via OMR -> music21 -> converter21) and the ground truth (obtained by exporting MEI from Sibelius), we find that most of the differences come from the fact that notes with 'accid.ges' are considered distinct from notes with simple 'accid'.

Attribute accid.ges is found in the ground truth, whereas accid is found in the predicted. I understand that "accid' means "performed + written" whereas "accid.ges" means "performed (but not written is the accid were met before in the measure).

Here is an example: at measure 8, the second A flat is marked as a difference by musicdiff. The MEI converter produced an 'accid' attribute, even though a first A flat was met before in the measure.

Ground truth note:

Predicted note

In Music21, I can see the displayStyle by default is "normal" (https://www.music21.org/music21docs/moduleReference/modulePitch.html#music21.pitch.Accidental.displayType) so my understanding is that the second A flat should be produced with "accid.ges".

Hope it is clear :-) So what can we do ? Is there any action to be taken in the music21 code ? Is there a change to to in the converter ? There is not OMR error there, only (IMO) a matter of encoding.

Thanks a lot

Philippe

ground_truth.mei.xml

predicted.mei.xml

C006_0_diff.pdf

[gregchapman-dev]

This is going to get more complex, I think, so I will take this to email, and then summarize back here.

[gregchapman-dev]

Setting accidental.displayStatus (instead of accidental.displayType) fixes the issue by being more explicit. Setting accidental.displayType to "normal" and then calling score.makeAccidentals(...) to automatically set all the accidental.displayStatus fields is the other way to do this, but that makes less sense in this case because the OMR system knows whether or not the accidental is visible, so explicitly setting displayStatus to True or False on each accidental is the way to go.