Artists have created the illusion of depth on a flati surface for centuries. One of these eye-fooling techniques involves manipulating the relative scale of the visual elements. In the two-dimensional picture, larger objects appear closer to the viewer than smaller ones.

Figure 1: Three convergent grids representing one, two and three point perspective schemes.

Another method of creating depth called “one-point perspective,” uses convergent lines that merge and intersect on a horizontal line called the horizon. The point at which the lines converge is called the vanishing pointi. An element whose contours align with the perspective lines appears to recede in space. A picture cani have two vanishing points that share the same horizon, (two point perspective) and three vanishing points and two horizons (three point perspective) as in Figure 1.

Because these visual phenomena are a naturally occurring characteristic of sight in the 3-D world, we subconsciously drawi the conclusion that the flat shapes exist in space when we see them on a drawing, painting or photograph.

Digital technology has simplified the creation of accurate perspective drawing and both Photoshop and Illustrator have new features that can adjust an image’s perspective or create entirely new perspective drawings on the fly. Gone are the old perspective charts and onionskins that required the painstaking charting of convergent lines and accurate hand rendering of items that diminish in scale in a picture plane. I say good riddance to these dinosaurs.

Vanishing Act

First, let’s have a quick look at an older Photoshop standby, the Vanishing Point Filter that enables the quick automatic placement of elements onto a perspective grid that you draw. The elements magically conform to the convergent angles of the grid, thereby warping any image into the correct perspective.

Figure 2: The perspective grid created with the Plane tool in Photoshop’s Vanishing Point Filter. Figure 3: The image pasted into the grid conforms to the perspective lines.

To use it, copy an image conform to a particular scene’s perspective by pressing Command + C (Mac) or Control + C (Win). We will call this the target image. The target image should be sized to fit the area on the destination image before copying. Open the scene where the image will be pasted (we’ll call this the destination image) and choose Filter > Vanishing Point, which will display an interfacei with specific tools and features for creating accurate depth composites.

With the Plane tool drag a grid using the perspective lines of the destination image (see Figure 2). The grid can be refined with the Edit Plane tool, and additional planes can be created. Press Command +V (Mac) or Control + V (Win) to paste the target image into the destination image and drag it onto the grid. Viola! The image snaps into perspective as in Figure 3.

Vector Perspective

By Design, Adobe Illustrator CS5 is primarily used to create vector artwork. Vectors are composed of paths and points called Bezier curves. This latest version has a new feature that is similar to the Vanishing Point Filter in Photoshop except that instead of pixeli-based images, it forces vector objects to conform to a perspective grid. The Perspective tool is accessed from the tools paneli. When you click on the tool you initially see a two-point perspective grid.

Figure 4: Illustrator CS5’s new perspective tool can define a custom perspective grid with the Define Grid dialog box.

There are several “widgets,” or small circular points, on the grid that enable custom editing. The horizon—the top most horizontal line, and the ground (the bottom line) can be vertically repositioned by dragging one of the end points with the Perspective Select tool. This procedure changes the vertical point of view.

You can choose from one-, two- and three-point perspective grids in the View > Perspective Grid submenu. To define a custom grid, go to View > Perspective Grid > Define Grid to display the dialog box (see Figure 4). To define an active plane, click on the Plane Switching widget on the upper right of the art board to select one of the grids.

The magic happens when you drag a vector object onto a selected plane, as in Figure 5. It immediately snaps to the currenti plane’s perspective lines and appears to recede in space. By using the perspective tool, entire scenes can be constructed in perfect one-, two- and three-point perspective without the hassle of manually drawing convergent perspective guides and forcing objects to conform to them.

Figure 5: Vector objects automatically conform to the perspective lines when dragged onto the grid.

Perspective Transformations

Figure 6: Photoshop’s Perspective transformation feature warps elements into perspective when the corner handles are dragged.

Photoshop has a feature that transforms the contenti of one or more layers into perspective. The Perspective Transformation command can render layer content or a selected area into one point perspective and produce the illusion that the elements are receding in space. Click on one or more layers in the layers panel, or select an area with one of the selection tool. Choose Edit > Transform > Perspective. A bounding boxi appears around the extremities of the elements. To force the elements into perspective, drag one of the corner handles inward toward the center point of the left, right, top or bottom lines of the bounding box, as in Figure 6. The elements distort and appear to snap into a perspective plane.

An alternate method is to choose the Move tool and check the Show Transform Controls box in the Options bar. Press Shift + Option + Command (Mac) or Shift + Alt +Control (Win) and drag the corner handles.

Two Cool Tools

In Illustrator two tools work in similar manner to the Photoshop Perspective Transformation. Free Distort, found in the Effect > Distort and Transform submenu displays a dialog box that shows a blacki and white outline of the selected artwork surrounded by a bounding box. Drag the corner handles to distort the object into a perspective plane, as in Figure 7.

Figure 7: The Free Distort effect in Illustrator manually distorts vector objects into perspective.

Illustrators Free Transform tool will also produce a perspective effect. This technique is a little tricky because you have to press keys commands in a specific sequencei, none the less the Free Transform tool is yet another method of rendering vector art into a one point perspective reality. First, select the object or objects that you want to recede in space with the selection tool. Choose the Free Transform tool. Click and drag a corner handle and press Shift + Option + Command (Mac) or Shift + Alt + Control (Win) and continue to drag. If you press only the Option (Alt) key, you will shape the object(s) based on the direction you pull one corner handle. Press the Option + Command (Mac) or Alt + Control (Win) and you’ll skew the object(s). With all of these techniques, it is critical that you drag first and then press the keys and release the mouse before you release the keys.

Distortion Correction

Finally, I would like to discuss a feature in Photoshop that corrects perspective distortion that is a result of capturing an image with a digital camera equipped with a wide-angle lens that, depending on how wide the lens is, can result in mild to severe distortion. This resulting warp can often alter an image aesthetically and create an interesting point of view, however more often than not, at least some correction is necessary in order to soften the deformation of buildings and other geometric elements.

The Lens Correction filter is accessed through the Filter menu. The dialog box is a mini-interface that auto corrects lens based geometric distortion automatically. In Search Criteria choose the make and model of the digital camera and a specific lens profilei.

When you choose the Custom tab you can remove chromatic aberration (like red, green cyan or magenta shifts, but just as important you can move the vertical and horizontal perspective sliders to remove (or create) a different point of view (see Figure 8)

The Lens Correction filter and the other features are really handy for creating forced perspective in scenes. Altering the perspective can add depth and drama to your image and produce the illusion that picture plane is a magic window into another world.

Figure 8: The Lens Correction feature in Photoshop CS5 removes lens distortion and corrects vertical and horizontal perspective.