Friday Fundamentals: Tracing Rasterized Line Art in Illustrator

Today’s Friday Fundamentals (still Friday here in Colorado, plus I get a bonus hour because I’m really a Californian) celebrates the release of Deke’s updated Illustrator CC One-on-One: Fundamentals course. And because I’m in charge, I’m going to cover one of the first things I was ever interested in doing with Illustrator: tracing artwork.

Tracing Line Art in Illustrator

Tracing is handy when you have a rasterized bit of art (i.e. art that’s made out of pixels) that you’d like to turn into clean Illustrator vector-based goodness. Especially if redrawing in Illustrator is beyond the limits of your time, patience, or talent (as in my case). Speaking of my case, I was trying to duplicate a logo for a baseball league, which I inherited from a person who only left behind a tiny 150-pixel GIF file when his kids grew out of little league. In Chapter 6 of Deke’s updated course, he uses an intricate butterfly he drew with Sharpie and paper, then scanned into a TIF file. The process is the same.

Changing line art or other rasterized graphics into vectors has some advantages, as you can imagine. The biggest of these involves, well, making the biggest art. Like the giant laminated posters I was trying to plaster all over town to encourage baseball registration. Since vectors are mathematically defined, you can blow your graphics up as large as you like and keep all the beautiful smoothness your baseball bats, butterflies, or other beauties deserve.

Here are the key things to know about tracing in Illustrator that I learned from Deke’s course, which apply to CS6 (and really CS5 if you can get over the interface differences), as well:

1) Decide whether you want to link to your original file or embed it in your Illustrator document:

There are two ways to apply Illustrator’s tracing function to your original file. You can embed the file directly into a new document by simply opening said original with Illustrator. Or, you can place the file into an already created document (using the File > Place) command, a process which links to the original without embedding.

As you can see below, the visual results of the trace are identical:

You can embed or link your rasterized art into Illustrator for tracing

But you can also see that the options are slightly different. When you embed the file, it simply becomes part of your document forever. This is good if you need to keep track of that file without worrying about losing access to its location, drive, server, etc.

However, in many (daresay most) cases, linking the file is advantageous. First, the Illustrator file remains smaller. But perhaps more interestingly, linking means you can make changes to the original, and the trace will actually update because the tracing function in Illustrator is dynamic. At any time, you can use the Edit Original button in the options bar to open your file in it’s assigned application. (In this case, the original is a TIF, so on my computer it would open in Photoshop.) Any time the original is edited, Illustrator informs you that the link needs to be updated:

Illustrator lets you know your linked file needs updating

Clicking Yes in this case causes the trace to be redrawn based on the changes in the original. There’s also a link in the options bar if you need to see where the original is hiding. 

Either way you choose to go, once you’ve got your original in place, select it in the Layers panel and click Image Trace in the options bar.

At which point, you may find out that….

2. Illustrator thinks you want a low res rasterized file to work from; you probably don’t.

If you bring in a fairly high resolution rasterized file, when you go to trace it, Illustrator will warn you that it may take a bit of computational time to do so. In fact, it may make the following suggestion:

I’ve purposely checked Do not show again because, frankly, Illustrator doesn’t know what I want. As you can see below, the low res original (on the left, below) resulted in a trace that’s far less detailed than one based on the high res image (on the right). So pour yourself a beverage, and let Illustrator take it’s time with your highly detailed file.

Compare Illustrator tracing with a low and high resolution original.

3 ) After the initial trace, you can adjust the results in the Image panel.

In the case of Deke’s butterfly, there were some stray marks (lint, smudges, dead insects) from the scan that needed cleaning up. You can access the Image Trace panel for fine-tuning by clicking as shown in the options bar. For getting rid of the schnivels (as Deke calls those stray scan marks because it’s more appetizing than “dead gnats”), increasing the Threshold setting to 70 sends more “grays” to white (whereas they had previously been interpreted as black, resulting in detritus floating around the butterfly.)

You can adjust your results in the Image Trace Panel

The second bit of fine-tuning in Deke’s case involves twirling open the Advanced part of the Image Trace panel and increasing the Noise setting. As you do this, keep an eye on the finer details of your image (like those in the blue box below) so that you don’t loose them along with the unwanted bits (as were previously in the red box below). What, you can’t see the stray dots in the red box? That’s because increasing the Noise to 50 got rid of them without damaging that delicate bit of butterfly filagree.

Increase the Noise setting to remove the final stray black dots

Turning on the Ignore White checkbox in this case also helps simplify the paths that get created. Technically, we only want to trace the black in this image (the white will take care of itself.) NOTE: Deke says I’m burying the lead here, and this is the KEY thing to turn on in the panel if you’re tracing a black and white image.) 

4) Expand is Illustrator code for “turn it into path outlines.”

Eventually, you’ll get the trace the way you like, but it won’t officially become path outlines until you tell Illustrator to do so by clicking the Expand button in the options bar. At that point, you’ll see the anchor points and path outlines magically appear.

Expand is Illustrator-code for

In the course, Deke goes onto explain how he uses the Shapebuilder tool to attach this half-butterfly with its flipped opposite. He also shares some handy advice for simplifying the path before doing so. The result is this lovely creature that was way to much fun to fill with various gradients for this effect. (Deke wants me to take credit for coloring this. Stay tuned for the Intermediate course—in a few weeks—to see how to do it easily with Live Paint.)

Note from Deke: click the image above to see a higher-res version. I wanted to see the damn thing up close, so I thought I’d make it available to everyone.

To watch Deke’s videos, check out Chapter 6 of the Illustrator CC course. If you’re not a member of, you can get a free week’s trial by going to Trace on, my butterflies!

Next entry:Illustrator One-on-One: Fundamentals, updated for Creative Cloud (Still Thriving)

Previous entry:Deke’s Techniques 239: Turn a Portrait into a Dot Drawing


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