This isn’t meant to be a complete or technically accurate description of Bezier Curves and how they work. (Plenty of video tutorials on YouTube that can explain that for you if you are interested.)
This is just a handful of quick demos showing how to use them in AI to do a simple manual trace.
The images used below would generally not need to be manually traced, because there are clearly defined color breaks in them. (The Illustrator AutoTrace function will give you very good results on this kind of image, but you need to be able to see the demos, so that’s why I’m using them.)
Where you would need to use this manual trace technique is where you have muddy delineations between the areas that you are trying to trace, similar colors that butt up against each other, photographs, or gradients.
Some very basic things to know going in:
Vector drawing means you’re creating a drawing by laying down Anchor Points and defining the Line Segments between them mathematically. (Fortunately, Illustrator does the math.)
The vector path lines are called a Stroke in Illustrator, and you can set the color and thickness that those display. The vector line runs down the center of the stroke unless you change it, so if you have a thick line showing, the vector line is right down the center.
Illustrator has two kinds of Anchor Points that it uses:
Corner Points: The lines that connect to these anchor points are locked at that point. (They only have one handle if they are curved, and none if they are straight lines.) Basically, it’s a point where an instant direction change occurs.
Curve (Smooth) Points: The lines that attach to these points interact with each other, through the magic of Bezier.
They rotate around the point. Pull on one of the two handles attached to the point in order to shift a line, and the line on the other side is going to compensate. (Imagine a teeter-totter.) Pull on a handle using the little blue dot at the end.
Straight Line Trace
This one is the easiest to implement by far. Basically you just:
- Drag your image file onto the artboard.
- Lock it. (Because otherwise it will “flash” diagonals at you as you click, which is distracting).
- Select the Pen Tool.
- Choose Zero (Null) Fill and a Contrasting Color for the Stroke (so you can see what you are tracing.)
- Click and release on the points that you want the path to follow.
- Basic editing for straight lines is as simple as selecting the Direct Selection Tool (White Arrow), clicking on a point and dragging it where you want it to go.
Converting Points using the Edit Tools
There are many times when converting between one type of point and another is extremely helpful during editing – the short demo below expands a little on the edit options before we move on to Tracing Curved Lines.
Curved Line Trace
Little bit trickier…few rules:
Click on a point, but don’t let go immediately.
Hold down the left mouse button and drag it for a short distance along the edge you want to follow to create the “handles” that you will use later to edit the curve. The closer you follow the edge going forward while you are dragging, the less editing you will have to do. The dragging motion before release tells Illustrator that you want to put a Curve (Smooth) Point there.
Release the mouse.
Place as many points as you think you will need, but try to place a point wherever the curve changes direction (slope). (The center point of an S shaped curve.)
If you want to set a Corner Point, do not drag, just Click, Release and then click on the next point.
When you get a little bit more comfortable with the motion, you can keep dragging until the curved line behind the new point conforms to the shape you are trying to hit before letting go.
In the demo below, I’ll show what you should (and shouldn’t) do when tracing, so we can reinforce some tricks in Editing.