Adaptive Wide Angle works on an ingenious and simple concept: you tell the filter which lines in the image are horizontal, vertical or straight-edged in real life, and it can use that information, along with any available lens data, to remove or lessen the distortions in those areas of the photograph. The end-result is often a less distorted image that requires less cropping than traditional transform correction methods. Note: as with any feature that transforms the pixels in your image, some cropping will be necessary afterward to remove gaps left around the edges.
Begin the process by identifying lines or edges in the frame that you know to be perfectly straight (in the real world) and which are perfectly vertical or horizontal (or close to it). Depending on several factors relating to the design of your lens and its distance to the subject, the lines may display some curvature. For this shot there are some tricky areas because there are curved surfaces used in the design of the building; however there are a couple obvious candidates for a vertical reference (Figure 3). For this structure, it is the gap between the walkway panels.
Figure 3: Try to find objects or edges in your scene that you know to be perfectly straight (or close to it) in the real world; this is your starting point.
Using the Constraint tool, move the cursor over the origin of your chosen “straight edge.” As you do this, a magnified view of the pixels under the cursor is presented in the Detail area (Figure 4). This is very helpful when working from small screens because it allows you to see exactly where you are placing your Constraints, even if the preview is zoomed out so that you can see the whole picture.
Figure 4: Use the Detail view to help you place your constraint anchors in precise locations.
To place an “anchor point” so that Photoshop can draw the constraint, click once. Next, move your cursor to the opposite end of the straight-edged object. As you do so, Photoshop will create a cyan line that should follow the contour of your edge, even if it has some curvature to it. When you reach the spot where you’d like to add the second anchor point (every constraint has two), click again.
The result is an “Unfixed Constraint” (meaning it is a straight edge not yet defined as being purely vertical or horizontal -- usually all three types of constraints are used at least once in this type of shot). Each Constraint has 3 components (Figure 5:): a line segment that defines the “angle” of the Constraint, two square anchors (also used as handles for moving or extending the Constraint) at either end of the segment, and two white dots that act as rotation widgets, allowing you to spin the entire segment 360 degrees around a center axis.
Figure 5: Each Constraint has widgets for controlling its length, angle and anchor (or handle) placements.
You can extend the Constraint to the edges of the frame (if necessary) by pressing the Shift key, then clicking and dragging each anchor individually..As you might have guessed, the smaller a Constraint is, the more localized its straightening effect. Constraints that span the entire image will have a more pronounced effect, so keep that in mind as you add them to your image. Using the Shift key ensures that you will not stray from the original path of the Constraint. To tweak the position of either anchor point, just click and drag it, using the detail view as your guide.
To rotate a constraint, move the cursor over one of the white dots connected to the circle, then click and drag to one side or the other. As you do so, a Heads-up Display displays the change in angle (Figure 6). All of these mechanisms allow you to match the Constraint to the straight edge that youve chosen, as closely as possible.
Figure 6: Use the white dots to rotate your constraint if the ends don’t match up precisely with the visual reference in your picture.