Limn can always (barring bugs, of course) fit some sort of outline to the bitmap input. But its default fit is likely to be far from the ideal: character features may disappear, curves distorted, straight lines turned into curves and curves into straight lines, and on and on.
To control the fitting process, you must specify options to override Limn's defaults. To describe those options, we must describe the algorithm Limn uses to do the fitting, which we do in this section. We mention the options at the appropriate point.
The next section summarizes all the options, in alphabetical order.
Here is a schematic of the algorithm. The subsections below go into detail for each step. Except for the very first step, this is implemented in `limn/fit.c'.
find pixel outlines for each pixel outline: find corners, yielding curve lists for each curve list: remove knees filter if too small: fit with straight line otherwise fit with spline: set initial t values find tangents fit with one spline while error > reparameterize-threshold, reparameterize if error > error-threshold, subdivide and recurse if linearity < line-threshold, change to straight line revert bad lines align endpoints
10.1.1 Finding pixel outlines Extracting the edges from the bitmap.10.1.2 Finding corners Finding subsections of each outline.10.1.3 Removing knees Removing extraneous points.10.1.4 Filtering curves Smoothing the outlines.10.1.5 Fitting the bitmap curve Doing the fitting.10.1.6 Changing splines to lines Use straight lines where possible.10.1.7 Changing lines to splines Sometimes it isn't possible.10.1.8 Aligning endpoints If points are close enough, line them out.10.1.9 Displaying fitting online Seeing the results as Limn runs.