Reflections on Reflections

There's been lots of interest lately in creating images of objects sitting on highly-reflective surfaces. This column will take a look at a few general principles to keep in mind when creating reflections.

The primary concept to remember is "realism." If the reflection doesn't behave as it would in nature, it will stick out. The viewer may not know what is wrong, but it will be obvious that something is wrong.

Two problems that you may notice are rotating rather than flipping a reflection across an axis, and reflecting the wrong side of an object. In this image, the letters have been flipped across the line of reflection correctly.

In this image, the copy of the letters has been rotated rather than flipped.

In the next example, the reflection is at a strange angle, but that's not the real problem. When you analyze the image you'll see that the wrong side of the calculator has been reflected. Since the shiny surface is behind the calculator, the back of the object should be reflected. When this problem occurs with peoples' heads, it appears as if a ghost is looking out from the mirror or window or other reflective surface.

The need to reflect the "back" of an image occurs when the reflective surface is placed behind the subject. Since Photoshop is a 2D image editor, there usually isn't a "back." In the following example, a second image (from the same source as the first) is used to form the reflection.

The same pair of images can be reversed (and rotated and scaled) to present another view:

Another important part of natural-looking reflections is the angle. In a simplification, think of the position of the reflection as the product of three points in space: the original, the reflecting surface, and the viewer's point of view. While the appearance of a reflection is affected by the position of a light source, the position of the reflection itself is not.

The angle of the reflecting surface determines the angle of the reflection. Try this: Hold a mirror in one hand. With the other hand, place the point of a pencil directly on the surface. Rotate the mirror (keeping the pencil vertical) and watch the change in reflected angle.

Another trap to avoid is not matching the reflecting surface. In this example, exaggerated ripples have been added to simulate water flowing along a street. Compare the reflections.

In the next installment of this series, we'll look at some basic reflection techniques.