iPhoto 6
Authors: Pogue D.,  Story D.
 Published year: 2006
 Pages: 69-70/183
Buy this book on amazon.com >>

6.12. Exposure

Most of the sliders in the Adjust palette affect the histogram in some way. But where do you begin?

Here's a general suggestion: Make exposure adjustments first. In the simplest terms, the Exposure slider makes your picture lighter when you move it to the right and darker when you move it to the left.

Its effects differ slightly depending on which file format a photo has:

  • When you're editing JPEG graphics (that is, most photos from most cameras ), the Exposure slider primarily affects the middle tones of a photo (as opposed to the brightest highlights and darkest shadows). If you're used to advanced programs like Photoshop, you may recognize this effect as a relative of Photoshop's gamma controls. (Gamma refers to the middle tones in a picture.)

  • When you're working with RAW files, however (Section 4.2.6), Exposure is even more interesting. It actually changes the way iPhoto interprets the dark and light information that your camera recorded when it took the picture. A photographer might say that it's like changing the ISO setting before snapping the pictureexcept that now you can make this kind of change long after you snapped the shutter.

    The Exposure slider demonstrates one of the advantages of the RAW format. In a RAW file, iPhoto has a lot more image information to work with than in a JPEG file. As a result, you can make exposure adjustments without sacrificing the overall quality of the photograph.

Watch the data on the histogram as you move the Exposure slider. Make sure you don't wind up shoving any of the "mountain peaks" beyond the edges of the Histogram box. If that happens, you're discarding precious image data; when you print, you'll see a loss of detail in the darks and lights.

The first step in fine-tuning a photo, then, is to drag the Exposure slider until the middle tones of the picture look acceptable to you (Figure 6-10). You can't add details that simply aren't there, but brightening a dark shadowy image, or deepening the contrast on a washed-out image, can coax out elements that were barely visible in the original photo.

If the dark and light areas aren't yet perfect, don't worry; you'll improve those areas next with the Levels control.



6.13. Adjusting the Levels

After you've spent some time working with the middle tones of your picture, you can turn your attention to the endpoints on the histogram, which represent the darkest and lightest areas of the photo.

If the mountains of your graph seem to cover all the territory from left to right, you already have a roughly even distribution of dark and light tones in your picture so you're probably in good shape. But if the graph comes up short on either the left (darks) or the right (lights) side of the histogram, you might want to make an adjustment.

Figure 6-10. Top: Here's a promising landscape shot that will serve as the basis for all the Adjust-panel manipulations described in this chapter. The camera was in Program mode, with Auto White Balance turned on. Unfortunately, you can see by looking at the histogram that much of the tonal information is bunched in the middle of the graph. As a result, the photo looks a little "flat," without much contrast.
Bottom: Step one in the repair job, then, is to move the Exposure slider a little to the right to improve the midtones. Because the graph in the histogram is elongated as a result, you've also improved the contrast.

To do so, drag the right or left pointer on the Levels slider inward , toward the base of the "mountain" (Figure 6-11). If you're moving the right indicator inward, for example, you'll notice that the whites become brighter, but the dark areas stay pretty much the same; if you drag the left indicator inward, the dark tones change, but the highlights remain steady.

Tip: Instead of dragging these handles inward, you may prefer to simply click the slider track itself at the outer base of the mountain. That's faster and gives you better control of the handle's landing point.
Figure 6-11. Here's that same photo, now showing the results of the second Adjust panel tweak: You've moved the endpoints of the Levels slider inward, boosting the shadow and highlight tones. In this case, moving them all the way to the point where they're touching the sides of the "mountains" would overdo it, creating too much contrast for this particular image. The base of the mountains is usually your target, but the visual results should always be your primary guide. Besides, you can always perform additional tweaks using the Brightness and Contrast sliders.

In general, you should avoid moving these endpoint handles inward beyond the outer edges of the mountains. Doing so adds contrast, but also throws away whatever data is outside the handles, which generally makes for a lower quality printout.


iPhoto 6
Authors: Pogue D.,  Story D.
 Published year: 2006
 Pages: 69-70/183
Buy this book on amazon.com >>

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