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DigPhoto / Shoot Like a Pro! Digital Photography/ King/ 2949-7 / Chapter 5
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Shoot Like a Pro!
When a sharpening filter finds an edge, it brightens the pixels on the lighter side of the edge. Pixels on the dark side of the fence line get darker. Figure 5.4, which shows a portion of a close-up photo I took of an antique adding machine, illustrates the effect. The left half of the image is the unsharpened original; the right half has been sharpened. In the sharpened half of the image, you can see the light and dark sharpening “halos” along the boundary between the number and the button face and also along the border between the button face and the background. When you view the image from FIGURE 5.4 Sharpening adds light and dark a distance, this increase in contrast fools your eye halos along the boundaries where into thinking that the picture is more sharply color changes occur. focused, as illustrated by Figure 5.5. Although the sharpened image in Figures 5.4 and 5.5 does appear to be better focused, the sharpening in both cases is really overdone. (I purposely applied too much sharpening so that you could clearly see the effect.) With this much Original Sharpened sharpening, surfaces that should appear smooth, such as the machine background, take on a sandpaper-like texture. In addition, extreme sharpening halos give the image an “outlined” look—as if someone had traced around the edges with black and white pens. As with compression and resolution defects, oversharpening defects are more noticeable in close-up images than in long shots. Page 22 of the color insert shows another example of how oversharpening can ruin an otherwise lovely close-up. I took all four pictures with the same camera; like many FIGURE 5.5 The increased contrast produced
Original
Sharpened
by the sharpening filter creates the illusion of sharper focus.
P:\010Comp\VirClass\949-7\ch05.vp Tuesday, June 24, 2003 5:14:00 PM