Improving Brightness and Contrast

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Improving Brightness and Contrast

You might think that when your photo needs some adjustment to its brightness or contrast, you should head right to A djust > B rightness and Contrast > B rightness/Contrast. Nothing could be further from the truth. Stay far, far away from Brightness/Contrast when editing your photos. Brightness/Contrast affects the whole image uniformly, when what you really want is to be able to adjust different parts of the tonal range separately. The commands of choice here are Levels, Histogram Adjustment, and Curves (with perhaps a touch of Clarify afterward).

Levels

Levels is one of the best operations for adjusting brightness and contrast, especially for black-and-white photos. It enables you to make separate adjustments in the shadow, midtone, and highlight areas of your photo.

Figure 8.7 shows the dialog box for Levels.

Figure 8.7. The Levels dialog box.

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The left and right Input levels sliders adjust the contrast, making shadows darker when you move the left slider to the right and making highlights brighter when you move the right slider to the left. The middle Input levels slider adjusts the brightness of the midtones. In general, after pulling the left and right sliders in toward the middle to adjust the contrast, you'll need to lighten the midtones by moving the middle slider to the left.

Histogram Adjustment

Histogram Adjustment is also great for adjusting brightness and contrast. In fact, some folks swear there's nothing better. Take a look at the Histogram Adjustment dialog box, in Figure 8.8.

Figure 8.8. Histogram Adjustment.

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Don't let all those controls and that graph confuse you. The graph is a histogram, a representation of the brightness values in your image. The left side represents the dark pixels (at the shadow end of the image's tonal range), and the right side represents the light pixels (at the highlights end of the range). The middle represents the midtones.

The only controls you'll probably ever need to use in Histogram Adjustment are Low (for the low clip limit) and High (for the high clip limit), Gamma , and sometimes Midtones: expand or Midtones: compress . In general, you should move the Low Clip to where the graph starts on the left and move the High Clip to where the graph starts on the right, as shown in Figure 8.9.

Figure 8.9. Adjusting the Low and High Clip .

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Adjusting the High in this way makes the brightest highlights pure white, and adjusting the Low in this way makes the darkest shadows pure black. What this does is ensure that the brightness of the image spans the whole tonal range from black to white.

NOTE

graphic/p3.gif CAUTION

Try to limit the Low and High adjustments to values of 0.1 or lower. Too high a value for the Low and you'll lose detail at the shadow end. Too high a value for the High and you'll lose detail at the highlight end.

After adjusting the Low and High , which affect the contrast of your photo, adjust the Gamma , which affects brightness. Be careful heresmall adjustments are usually best.

Once you've adjusted the Gamma , you may also want to adjust the Midtones slider. Midtones: compress lessens the contrast in the midtone range, while Midtones: expand heightens the contrast in the midtone range. Be careful heretoo much compression can cause loss of detail, and too much expansion can introduce noise (random specks of color ).

Curves

Curves is also touted by some as the best operation for adjusting brightness and contrast, vying with Histogram Adjustment for that honor .

Curves lets you fine-tune brightness and contrast along the whole tonal range, from shadows to highlights, adjusting any number of subranges. To see how, take a look at the Curves dialog box, shown in Figure 8.10.

Figure 8.10. The Curves dialog box.

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The graph in Figure 8.10 represents the input and output brightness values along the whole tonal range, with shadows represented at the left side and highlights on the right, with black at the bottom and white at the top. When you open Curves, the graph is a straight line from the lower left to the upper right, because the input and output values match up 1-to-1 before you make any adjustments.

You make adjustments by dragging any node on the curve. When you begin, there are only two nodes, one at the far left (for black) and one at the far right (for white). To add new nodes along the curve, just click on the curve. To lighten pixels at any point, click a node and drag upward. To darken pixels at any point, click a node and drag downward. Figures 8.11 and 8.12 show examples of each.

Figure 8.11. Lightening areas of an image with Curves.

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Figure 8.12. Darkening areas of an image with Curves.

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You can even produce a negative version of your photo with Curves. Just drag the leftmost node to the top and the rightmost node to the bottom, completely inverting the original curve. An example is shown in Figure 8.13.

Figure 8.13. Creating a negative version with Curves.

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Contrast in any area is affected by the steepness of the graph in that area. The steeper the curve, the higher the contrast. Figures 8.14 and 8.15 show examples of increasing the contrast in the midtone region.

Figure 8.14. Increasing the contrast in an area by increasing the graph's steepness.

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Figure 8.15. Increasing contrast even further.

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A commonly used rule of thumb is that a photo benefits by having a slightly S-shaped curve, as in Figure 8.16.

Figure 8.16. An S-curve can benefit many photos.

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There are many exceptions to this rule, though, so don't be a slave to it. Especially keep in mind that what this curve does is increase the contrast for the midtones by sacrificing detail in the shadow and highlight ranges.

One problem with Curves is that it can produce unintended changes to your image's color. To avoid this problem, try the following technique:

  1. Duplicate the Background layer of your photo.

  2. On the duplicate layer, apply Curves.

  3. Set the Blend Mode of the duplicate layer to Luminance.

  4. Adjust the duplicate layer's Opacity until you get the effect you want.

A variation on this technique is to use a Curves adjustment layer. Make your adjustments to the curve on the adjustment layer. Then set the adjustment layer's Blend Mode to Luminance and adjust the adjustment layer's Opacity until you get the desired effect.

NOTE

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For adjusting brightness and contrast, the Channel control for Curves should be set to RGB. Curves can also be used to adjust the Red, Green, and Blue color channels separately to make color adjustments. For example, you can set Curves to Red and pull down the node at the highlight end to lessen the amount of red in the highlight and upper midtone range.

NOTE

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Curves isn't just for straightforward adjustments of contrast, brightness, and color. As you'll see in Chapter 10, "Tricks and Techniques," you can also use it for special effects, including producing some rather realistic metallic effects.

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Paint Shop Pro 8 Power
Paint Shop Pro 8 Power!
ISBN: B001QCXEI6
EAN: N/A
Year: 2006
Pages: 125
Authors: Lori J. Davis

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