Working with Vectors

Learning how to manipulate paths is the key to using Photoshop 6's new Shape tools. Photoshop users who haven't upgraded, read along! We'll be working a lot with the Pen tool in this first installment.

The line between vector and raster/bitmap programs is blurring more and more. First Illustrator 9 got transparency, then Photoshop 6 got vector type and the Shape tools. To get the most out of both vector shapes and the Pen tool, you should really understand paths and how they work. In this week's column, we'll look at the theory of paths as we know them, a bit about their history, and how to create paths with the Pen tool.

There are two terms that are directly tied to paths. The term vector is used to define art crated with paths. (Illustrator, for example, is a vector art program.) The term relates directly to paths in Photoshop through the direction lines. A vector is a quantity that has both magnitude (the length of the direction line) and direction (its angle from the anchor point). The second term is Bezier curve. Pierre Etienne Bezier (the first “e” should carry the French accent aigu), a long-time employee of the auto maker Renault, developed the system which we use today. Bezier (1910-1999) saw these curves as a way to transfer auto body design information to the factory. While it took years for him to convince Renault to accept the system, it has found its way into many facets of life. Bezier curves are even at the heart of the desktop publishing revolution, being integral to Adobe's PostScript page description language. Vector art is based upon and created with Bezier curves, but you can call them “paths.”

Paths are among Photoshop's most powerful tools. Incredibly precise selections can be made, saved, and moved from file to file. Paths can be stroked and filled, which is the basis for Photoshop 6's new Shape tools.

Now that we've got some of the background, it's time to get to work. Let's start with a look at the components of a path, their names, and what they do.

In the figure above, you see the anchor points, the path segments, direction lines, and control points. The segments constitute the path itself. The anchor points determine where the path segment will go. The direction lines, which are manipulated with the control points, determine the shape of the segment.

The relationship between the anchor points and the directions lines is the key to creating and editing paths and vector shapes. Anchor points come in two varieties, corner points and smooth points. A corner point is one at which two path segments join at an angle. A smooth point is one at which two path segments join in a continuous curve. The difference is shown in the next figure.

On the left is a corner point with no direction lines. (It was formed by clicking with the Pen tool.) In the middle is a smooth point. (Create these by clicking and dragging with the Pen tool.) To the right is a corner point with direction lines. (These are created from smooth points with the Direct Selection tool.) The path segments leading into each type of anchor point can have any type of point at the other end. The segment's shape will be determined by both of the points and their direction lines.

As you can see below, the length of the direction line has as much to do with a curve's shape as does the direction line's angle.

Creating a path can be as simple as clicking with the Pen tool. Clicks set the anchor points and to curve the segments, simply drag. The next figure shows a simple path template. (You can save this file to disk by right-clicking or Control-clicking (Mac).)

The direction in which you drag when creating a smooth anchor point will determine whether the curve will be simple (a single curve) or complex (an “S” curve).

Once a point has been placed, it can be edited with the Direct Selection tool. In Photoshop 5 (including 5.5), the Direct Selection tool, whose icon is a white arrow, is in the hidden palette under the Pen tool. For Photoshop 6, it's been moved to a spot under the new Path Component Selection Tool (to the left of the Type tool in the Toolbox). Click on a point to make it active. It can then be dragged to a new location, or you can drag the control points to change the shape of the segment.

An anchor point can be converted between corner and smooth with the aptly-named Convert Anchor Point tool. In both Photoshop 5 and Photoshop 6, you'll find it below the Pen tool. To change a corner point to smooth, click on the point and drag to create direction lines (shown below). To convert a smooth anchor point to a corner anchor point, simply click without dragging.

By default, a curve will run smoothly through an anchor point. To have the segments on either side of an anchor point asymmetrical, Option-drag (Alt-drag on Windows) a control point with the Direct Selection tool.

Photoshop also has Tools called Add Anchor Point and Delete Anchor Point, which are both available to edit paths. Position the Add tool over any segment of a path and click to insert an anchor point. Place the Delete Anchor Point tool over any existing point and click. The path segments on either side will be joined into a single segment, with the shape determined by the remaining direction lines.

Paths can be open or closed. To close a path, such as that in the template seen above, click again on the first point. (You can drag that last click, too, to create a smooth anchor point.)

Once you start a path, it appears in the Paths palette as Work Path. A work path is discarded as soon as you start the next path. You can, however, save your work by double-clicking Work Path in the Paths palette and giving it a name.

In the next installment, we'll look at some of things that you can do with your paths, the Paths palette, and the Freeform and Magnetic Pen tools.