Tracer

This tool lets you autotrace the images assigned to glyphs. It applies several simplification algorithms to reduce the complexity of the traced outlines.

Trace

• Threshold: The value to be used when converting the image to a black and white bitmap.
• Tolerance: The tracing accuracy tolerance. A higher number will result in less accuracy.
• Turd Size: Suppress speckles (aka turds) below this size.
• Blur: The amount to blur the image before converting to a black and white bitmap.

Tracer uses the autotracing implementation in DrawBot. DrawBot uses Potrace. So for complete documentation on trace settings, refer to these links.

Simplify

• Segment Count: Contours with fewer segments than this number will be discarded.
• Small Curves: Curves shorter than this number will be converted to lines.
• Small Contours: Contours with an area smaller than this number will be discarded.
• Douglas Peucker: Apply the Ramer–Douglas–Peucker algorithm.
• Visvalingam Whyatt: Apply the Visvalingam Whyatt algorithm.
• Shallow Curves: Convert curves with a curve length that is similar to a line from the same on curve points to a line.
• Spikes: Remove those spiky points that autotracing is notorious for producing. Well, try to remove them at least.
• Remove Overlapping Points: Remove overlapping points.

If you don't want any simplification, set all of the values to zero.

Destination

• Layer: The name of the layer the trace should be stored in. If the given name doesn't exist, a new layer will be created.
• Trace Selected Glyphs: Trace the glyphs selected in the list.
• Trace All Glyphs: Trace all of the glyphs in the list.

Preview

This gives you a preview of tracing with the input settings. The button below will let you customize what you are seeing.

Scripting

The internals of this extension are accessible via Python. You can get the documentation for the various functions and classes by getting the docstrings from these.

import tracer

tracer.traceGlyphImage
tracer.simplifyGlyphContours
tracer.countGlyphPoints
tracer.SimplifyContoursPen
tracer.CountPen

You can also look at the source code.