Join Mordy Golding for an in-depth discussion in this video Making vector-based adjustments, part of Illustrator CS4 Beyond the Basics.
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We know that by using the Live Trace feature inside of Illustrator, we can trace objects using the fill tracing method, the strokes tracing method or combination of fills and strokes. But whether you use fills or strokes, when you trace your objects, there are many other settings that apply to how Illustrator precisely converts the pixels into paths. So let's take a look at some of these vector adjustments. I'm going to start off by selecting this object right over here. Let me zoom in on really close, so we could see what we are doing, and I'll position that just over here on the left side of the screen.
With the object selected, I'll simply go ahead and open up my Tracing Options dialog box, and I'll click on the Preview button so I can see what's happening here. Now because I'm using the default tracing right now, which uses a fills option, you can see that these two options here, Maximum stroke weight and Minimum stroke length, are currently grayed out. That's because these settings only apply when you are using the strokes option. So I'll go ahead and I'll turn strokes on. Let's turn off fills now for a moment, so that we can see what these two settings do. The Maximum stroke weight defines how thick of a stroke or how heavy of a stroke Illustrator can use when tracing the object. You'll notice that it has some strokes that are very thin in weight, and some that are much heavier. This setting simply determines how thick of a stroke Illustrator can use. Sometimes I may reduce this to a very low number, for example, like 1 pixel, just so that they are all consistent.
At the same time in this case here, it kind of does a trace where again the exterior of the object is traced, which doesn't really help me if all I want is a centerline of an object. I also have the ability to set a Minimum stroke length, which gives me control over how long each path will be that is drawn. By setting a higher number here, I'll ensure that I don't get all these minuscule paths that are broken up inside of my trace. In this particular example, I really won't see a difference by changing this value, because I have one long continuous path. There are three of those settings that are here. One is called Path Fitting, Minimum Area, and Corner Angle.
For now, let's take a look at the Path Fitting and Corner Angle Settings. To better illustrate what these settings do, I'm going to turn the fill setting back on, and turn off strokes. What the Path Fitting setting does, it actually controls how close the vector path match the underlined pixels. In general, using a low number for Path Fitting will increase the number of anchor points used in my trace. And I'll close the trace to closely match exactly how the pixels are positioned. Using a higher number, it starts to reduce the number of anchor points used and also smoothes out the path.
Let me show you what I mean, if I change my Path Fitting here for example to 0. That means that the trace that I create is actually going to match perfectly, to the way the pixels are. Now because this is a low-resolution image, the trace is now simply drawing over the exact edges of the pixel. Now if I'm going ahead, and I'm looking for a nice, smooth and clean path, this is certainly not the way to go. In addition, take a look at how many anchor points I have now. By setting my Path Fitting setting to 0, I now have close to 20,000 anchor points in my object. By going to the default setting of 2 pixels here, now do I see a nice, clean smooth path. I have also reduced the number of anchor points to 323. Overall, the Path Fitting setting is probably one of the most dramatic effects on the appearance of your trace. I use a higher number, for example, 4 pixels, and you will see that now the paths start to smooth out even more, and also seem to take on some kind of interpretation on their own, rather than matching the pixels perfectly, it's just using them as a base to create some new type of artwork. Let me set it back to the 2 pixel setting, which is the default setting that's here, and let's take a look at the Corner Angle setting.
Now right now in this trace I have some points that are here, and then I have some smooth areas as well. The Corner Angle setting simply determines at what point the paths anchor points become smooth anchor points, rather than corner anchor points. For example, focus on these nice smooth lines that appear here on the trace. I'm going to set my Corner Angle here to 0, again to the extreme, and you can see that now instead of a smooth line, it kind of has a little point here, and a point here as well. Notice these other points that appear here. By increasing the corner angle, I'm telling some of those points to convert into smooth curves. The higher of a number I go, and I can go all the way up to 180, the smoother or rounder the edges of my artwork get, even these areas that were pointy before, now have a little bit of a roundness to them.
So now that we know what Path Fitting and Corner Angle do, that leaves us with two more settings here in the Trace Settings area and the Tracing Options dialog box, and that's Minimum Area and Ignore White. Let's cancel out of this particular object here, I'm going to zoom out for a second here, then focus on this piece of artwork right here, and move up towards the top of the screen here, and once again, I'll open up my Tracing Options dialog box, and click on the Preview button. The Minimum Area setting determines the size for how bigger region needs to be in order for your Illustrator to trace it. In other words, if I have a really small little spec or little area of pixels in my original image, the Minimum Area setting might allow me to ignore that particular area, and not trace it at all.
In other words, the Minimum Area allows me to control how much detail the Live Trace feature actually pays attention to. For example, take a look over here. I have some highlights in this person's ear. Right now these areas are more than 10 pixels in size, so that's why Illustrator traces them. But if I were to increase this number to maybe 60 pixels for example, you will notice that those areas start to disappear. Because they are smaller in size than 60 pixels, Live Trace simply ignores them and makes believe that they are not there at all. If you have an image that has a lot of detail inside of it, by increasing your Minimum Area, you are telling Illustrator to ignore those smaller areas of detail and not trace them.
If you want more detail in your image, you would lower your Minimum area. For example, if I set my Minimum area to 4 pixels, I'll start to see more area show up over here than it is here. When using a Black & White trace inside of Illustrator, you will see that the Minimum Area setting also appears in the control panel. Finally, there is the Ignore White setting that's right over here. Now we specified a Black & White trace. That means that Illustrator is taking a color photograph and converting it to black & white objects. But let's say I don't want white object. Let's say I want some kind of background to show through in these areas. By choosing the Ignore White option, Illustrator actually sets these areas to None instead of White. Allow me to place my Live Trace artwork on top of a colored background, and having that colored background show through where the areas are white.
Now that you know what each of these vector adjustments do, you have the tools that you need to get the result you are looking for from Live Trace.
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