TechNote (Archived)

FreeHand Autotrace for Beginners

Understanding Autotrace

The FreeHand Autotrace tool converts bitmap objects into vector paths. In addition, FreeHand can also autotrace other vector objects which may already be on the page.

Understanding the basic features

Color Mode

How many colors do you want to extract from your scan? The initial settings start with 2 and end with 256, but you can enter any number you like into the field. The more colors you expect FreeHand to convert, the longer the trace will take. More colors will also require more RAM, and if you attempt to trace a large object at 256 colors you may run out of memory.

You can also choose to trace your scan using a grayscale palette, eliminating all color information from the subsequent PostScript objects.

Resolution

How detailed do you want the trace to be? Again, more detail takes longer to trace and takes more memory.

Trace layers

FreeHand has a unique autotrace tool. No other tracing tool can trace bitmaps AND vector paths. Because of this feature you need a way to tell FreeHand which objects on the page you wish to trace. For example, you might have a scan on the background layer and some vector paths on the foreground layer. If you want to trace the vectors, choose "Foreground" in Trace Layers. If you wish to trace both the scan and the vector objects, choose "All".

Path Conversion

Because FreeHand can draw with both filled, closed paths and open paths, we have to make some decisions about how we want to trace.

Outline

This feature converts all like-colored areas to filled, closed FreeHand objects, stacked on top of each other. It is very basic, but it can give you excellent results for tracing black and white line art. Remember, the quality of the trace depends on the resolution quality of the original scan.

Centerline

Using the same basic areas of pixel color as Outline, the centerline affect creates a stroke at the center of these areas. There will be no filled objects. This option is good for capturing fine detail in pen and ink sketches.

Outline/Centerline

This option uses both techniques described above. It provides more detail, but is a more complex PostScript drawing.

Outer Edge

This feature traces only the outer edge of the scan or path. This technique is very useful for creating quick masks to use as an alpha channel or a container for a paste inside.

Trace Conformity

This variable lets you instruct FreeHand how close to the trace it should "stick" to the pixels it's tracing. Looser settings will ignore detail, concentrating on tracing larger areas of consistent color. A tighter trace will attempt to create a path that follows every detail and line in your scan. Playing with this value can give you some interesting creative results.

Noise Tolerance

Every scan has "stray" pixels which you didn't intend as part of the original art. These may show up as a few single black pixels in a white background area, perhaps caused by dust on the glass of the scanner. A higher noise tolerance value gives you a vector path for every single pixel in the scan.

So, if your scan is very clean with crisp edges, you can generally afford to set this value toward minimum. But if your scan is very dirty, containing many fuzzy areas and lots of noise, you'll want to set this value to maximum. Experimenting with this value can save plenty of vector path cleanup.