Exposing to the Right

The best way to minimize the effects of banding in digital images is to learn how to make accurate digital exposures that place your highlights as close as possible to where they should be on the right edge of the histogram.

This is called "Exposing for the Highlights" and there are two reasons why this works.The first is fairly obvious. The second is more subtle but just as important and is discussed later in the section The Problem of Digital Shadows.

Exposing for the highlights is a valuable technique. Using the language of the Zone System, placing the Important Highlight on Zones VII or Zone VIII where they belong, minimizes the need to stretch out the image's pixel levels, which causes banding and posterization in the shadow areas.

Figure 94 shows the same image as the previous example but with an exposure designed to place the meter reading of the Important, textured white highlight values on Zone VIII. Any brighter areas of the subject are specular reflections that can be rendered as Zone IX.

Notice that when compared to Figure 91, the tonal values of this histogram are shifted substantially to the right. This is why this technique is often referred to as "Exposing to the Right."

FIGURE 94 Histogram of properly exposed digital image.

Figure 95 shows the adjustments made to match the contrast of Figure 91 as closely as possible.

FIGURE 95 Histogram of properly exposed digital image w/Levels adjustments.

FIGURE 95 Histogram of properly exposed digital image w/Levels adjustments.

Notice that only slight adjustments of the white, black, and middle gray sliders were necessary because the exposure was correctly placed on the Zone Scale.

The Zone System of Digital Exposure 141 Figure 96 is the image and histogram that resulted from these adjustments.

FIGURE 96 Histogram of properly exposed digital image after levels adjustments.

Note that, compared with the histogram from Figure 92 which is shown again below, there are far fewer pixel level gaps using this method and the gaps are much more evenly distributed across histogram.

FIGURE 92 Histogram of underexposed digital image after Levels adjustments.

A careful comparison of details from these two examples shows that proper exposure greatly improved the quality of the shadow areas.

FIGURE 97 Details of Shadow of Underexposed and Properly Exposed Digital Images. (a) Underexposed; (b) properly exposed.
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