Tonal Corrections
This chapter is from the book
This chapter is from the book
This chapter is from the book
Tonal corrections are those adjustments and changes you make to the brightness and contrast of your image. For years, Photoshop's workhorse tonal-correction tools have been the Levels control and the Curves dialog box, both of which can be applied either destructively or as adjustment layers.
The Levels control remains untouched in the Photoshop CS3 beta, but Adobe has made major changes to both the Curves and Brightness/Contrast tools. In addition, the program has new features for performing black-and-white conversions.
Curves
Curves has been around since version 1 of Photoshop, but it's never had a major revamping until now. Adobe has made several cosmetic and functional changes to the Curves control, some of which are obvious as soon as you open the dialog box (Figure 3.1).
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Figure 3.1 The Curves dialog box has substantial revisions in CS3.
First of all, the curve display itself is larger, which makes it easier to perform small, localized adjustments. And a histogram is displayed behind the curve now, allowing you to see exactly which parts of the curve correspond to specific tones in your histogram.
Cosmetically, the Curves dialog box has been spruced up with grayscale grid lines, rather than the old 1-bit dotted lines, and now when you drag a point on the curve, reference lines are displayed to help you see the correspondence between input and output (Figure 3.2).
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Figure 3.2 When you drag a curve control point, reference lines appear to show you the correspondence between input and output.
Directly below the curve display, you'll find black and white point sliders (Figure 3.3), just like you have in the Levels dialog box. These sliders make setting black and white much simpler for beginning Curves users.
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Figure 3.3 The new sliders let you use a Levels-like interface to set the black and white points in your image.
A new Show Clipping check box turns on a clipping display in your image, allowing you to see when you've pushed an edit too far. As in Levels, you can also see the clipping display by holding down Option/Alt while sliding the black and white point sliders. When Show Clipping is checked, clicking the Black eyedropper shows only shadow clipping, while clicking the White eyedropper shows only white clipping.
A new Curve Display Options section lets you customize how the curve is displayed (Figure 3.4):
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Show Amount Of. By default, the curve lets you control the brightness of the tones in your image. If you prefer thinking in terms of ink percentages, you can switch to Pigment/Ink %.
Figure 3.4 Use the settings in the new Curves Display Options section to control the look of the curve.
Channel Overlays. Curves has always allowed you to perform separate adjustments on each individual color channel. When the Channel Overlays option is checked, you can see each separate curve superimposed (Figure 3.5).
Figure 3.5 The Channels Overlay option les you see individual channel adjustments superimposed.
- Baseline. The baseline curve is a straight diagonal line from bottom left to top right. When you drag the curve, that baseline remains onscreen as a reference. If you'd rather have it hidden, uncheck the Baseline checkbox.
- Histogram. Use this check box to toggle the histogram display.
- Intersection Line. You can toggle the display of the intersection lines that appear when you drag a point by checking and unchecking this box.
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If you clear all the check boxes in the Curve Display Options section, your curve will look and act just like it would have in earlier versions of Photoshop.
Options
The Curves dialog box keeps all the options of previous versions and adds a few new items (Figure 3.6).
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Figure 3.6 The Curves dialog box provides several new choices in its Options palette.
The Algorithms section now gives you three choices for applying the curve to your image:
- Enhance Monochromatic Contrast clips all three color channels to improve contrast without altering the overall color relationship between the channels. This option is basically the same as the Auto Contrast command.
- Enhance Per Channel Contrast clips all three color channels independently and maximizes the tonal range in each channel to increase contrast but also neutralize color (remove color casts). This is the same algorithm used by the Auto Levels command.
- Find Dark & Light Colors performs an Auto Color instead of Auto Contrast adjustment. The image is analyzed to find the average lightest and darkest pixels. Those pixels are defined as shadow and highlight points, which are used to maximize contrast while minimizing clipping.
Snap Neutral Midtones automatically adjusts the individual channel curves so that the neutral tones in your image match the swatch shown in the Target Colors & Clipping section. If you'd rather have your image adjusted to a different tone, click the swatch and choose a different color from the color picker.
Finally, you can make your settings defaults by checking the Save as defaults check box.
Presets
The Load and Save options have been relegated to their own pop-up menu, but their functions remain the same (Figure 3.7).
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Figure 3.7 The Load and Save options have been moved to their own pop-up menu.
The new Preset menu provides single-click access to all your saved presets. What's more, the menu comes loaded with predefined presets (Figure 3.8).
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Figure 3.8 The Curves dialog box now comes preconfigured with an assortment of presets.