Last modified: October 27, 2015
In module gamera.toolkits.musicstaves.musicstaves_rl_fujinaga
This staff removal algorithm is based directly on Ichiro Fujinaga's staff removal code, though through the filter of two major rewrites, the first by Karl MacMillan and the second by Michael Droettboom.
This code is known to be functionally equivalent to Fujinaga's original code with the following exceptions:
A notable feature of this algorithm is that it attempts to straighten staves through deskewing, by shearing thin vertical strips up and down by cross-correlating them with their neighbors. This deskewing first happens globally on the page and then on each staff individually. This helps to rectify images where the staves
a) are not straight, as in the spine of a large book, or other anomalies in the printing
b) are not parallel with one another, as is often the case in older hand-printed music.
A consequence of this is that staffline detection is not easily decoupled from deskewing. The deskewing can not finish without knowing where the stafflines are, and the stafflines can only be found as the iterative deskewing takes place, (since stafflines are modelled as perfectly straight and horizontal line segments).
In the last rewrite of the code, staff removal was decoupled from staff finding and deskewing. So there are three separate functions available so that the removal step could be interchanged with something else:
find_and_remove_staves_fujinaga find_and_deskew_staves_fujinaga remove_staves_fujinaga
TODO: There's a lot more to explain here.
References:
| Author: | Michael Droettboom, Karl MacMillan and Ichiro Fujinaga |
|---|
Detects and removes staff lines from a music/tablature image.
Signature:
remove_staves(crossing_symbols='all', num_lines=5, skew_strip_width=0, max_skew=5.0, undo_deskew=False)
with
- crossing_symbols:
- Determines which symbols crossing staff lines should be kept intact. Supported values are 'all', 'bars' or 'none'. Currently ignored
- num_lines:
- The number of stafflines in each staff. (Autodetection of number of stafflines not yet implemented).
- skew_strip_width = 0
- The width (in pixels) of vertical strips used to deskew the image. Smaller values will deskew the image with higher resolution, but this may make the deskewing overly sensitive. Larger values may miss fine detail. If skew_strip_width <= 0, the width will be autodetermined to be the global staffspace_h * 2.
- max_skew = 5.0
- The maximum amount of skew that will be detected within each vertical strip. Expressed in degrees. This value should be fairly small, because deskewing only approximates rotation at very small degrees.
- undo_deskew = False
- since the fujinaga performs deskewing on the input image, it might be necessary to undo it, for evaluational reasons.
Returns the y-positions of all staff lines at a given x-position. Can only be called after remove_staves.
Signature:
get_staffpos(x=0)
with
- x:
- This parameter is currently ignored, but we do know where the left and right sides of the staff are, so we could do something with that.
The return value is a list of StaffObj.