Photoshop.CS.Bible [Electronic resources] نسخه متنی

Making Custom Brightness Adjustments

The Lighter and Darker options in the Variations dialog box are preferable to the Lightness slider bar in the Hue/Saturation dialog box because you can specify whether to edit the darkest, lightest, or medium colors in an image. But neither command is adequate for making precise adjustments to the brightness and contrast of an image. Photoshop provides three expert-level commands for adjusting the brightness levels in both grayscale and color images:

The Levels command is great for most color corrections. It lets you adjust the darkest values, lightest values, and midrange colors with a minimum of fuss and a generous amount of control.

The Curves command is great for creating special effects and correcting images beyond the help of the Levels command. Using the Curves command, you can map every brightness value in every color channel to an entirely different brightness value.

PhotoshopNew to Photoshop CS, the Shadow/Highlight command is great for altering the brightness levels of certain sections of an image without harming other sections. It provides for a different approach than the Levels command and is particularly good at fixing backlighting problems in images.

The Histogram palette

Choose Window Histogram to display the Histogram palette. At first, it seems like there’s not a whole lot to the palette. It saves you the trouble choosing the Levels command, but you don’t have access to any other information or the ability to select different channels. Unless, that is, you display the palette menu and choose Expanded View, as shown in Figure 17-20.

Figure 17-20: The Histogram palette’s expanded view gives you an impressive amount of information about the intensity levels of your pixels.

The expanded view is where you can explore the real power of the Histogram palette. It contains the following options:

Channel: The Channel pop-up menu lets you determine the types of values displayed by the Histogram palette. By default it’s set to the color mode in which you’re working. If you’re editing an image in either the Grayscale or Indexed Color modes, this menu is unavailable.

From the Channel menu, you can choose to display the default combined tonal levels or any of the color channels individually. Choose Show Channels in Color from the palette menu to display the individual channels in the colors they represent. Any additional channels you have created can also be selected from the Channel pop-up menu. Choose Luminosity to display a histogram of only the brightness levels in your image. Finally, you can call up an overlapping composite graph of all the color channels by choosing Colors.

Uncached Refresh:Chapter 2.)

Regardless of how you’ve set your preferences, the Histogram palette will automatically regenerate based on the image cache unless you click the Uncached Refresh button, labeled in Figure 17-20, which tells the palette to redraw the graph based on the current image. Photoshop provides a number of other ways — one might even say too many ways — to refresh the histogram. You can also click the cached data warning icon (labeled in Figure 17-20) that appears in the top-right corner of the histogram whenever you’re viewing a graph created from the cache. Additionally, you can accomplish the same thing by doubling-clicking on the histogram itself. Finally, you can choose the Uncached Refresh option from the palette menu.

Source: In a multilayered image, you can tell the Histogram palette to display values for either the Entire Image or just the Selected Layer from the Source pop-up menu. If the image contains any adjustment layers, select one of them and choose Adjustment Composite from the Source pop-up menu to display a histogram of the adjustment layer and any visible layers below it.

Below the Source menu in the expanded view, you’ll find statistical information about the image or layer, which you can toggle on or off by choosing Show Statistics from the palette menu. The details can be arcane, but they can also give you some useful information about the intensity values in your image. A couple of the more useful statistics include Level, which displays the intensity level at the spot under your cursor, and Count, which tells you the total number of pixels in the image that match a particular intensity.

One of the great strengths of the Histogram palette is the fact that it updates on-thefly, even while you’re working in one of the color adjustments dialog boxes (but only if you have the Preview check box selected). Even better, the palette doesn’t simply replace the original histogram will the new one; it keeps the original histogram visible behind the adjusted histogram in a grayed-out version. It’s almost as if you’re viewing the Ghost of Histograms Past, as you can see Figure 17-21. And that’s not all. You can also expand the Histogram palette to display a separate histogram graph for each color channel in your image, as shown in Figure 17-21. To do so, choose All Channels View from the palette menu.

Figure 17-21: Although it takes up quite a bit of screen real estate, the Histogram palette’s all channels view can be really useful when you need a quickie glimpse of the color intensity distribution in your image.

Although many of the other palettes become frozen when you’re working in a dialog box, you never lose access to the options in the Histogram palette. Well, almost never. You can’t access the Histogram palette options when the Filter Gallery window is open.

The Levels command

When you choose Image Adjustments Levels or press Ctrl+L (z -L on the Mac), Photoshop displays the Levels dialog box shown in Figure 17-22. The dialog box offers a histogram, which matches the combined tonal histogram found in the Histogram palette by default, as well as two sets of slider bars with corresponding option boxes and a few automated eyedropper options in the lower-right corner.

Figure 17-22: Use the Levels dialog box to map brightness values in the image (Input Levels) to new brightness values (Output Levels).

You can compress and expand the range of brightness values in an image by manipulating the Input Levels options. Then you can map those brightness values to new brightness values by adjusting the Output Levels options.

The options in the Levels dialog box work as follows:

Channel: Select the color channel that you want to edit from this pop-up menu. You can apply different Input Levels and Output Levels values to each color channel. However, the options along the right side of the dialog box affect all colors in the selected portion of an image regardless of which Channel option is active.

Input Levels: Use these options to modify the contrast of the image by darkening the darkest colors and lightening the lightest ones. The Input Levels option boxes correspond to the slider bar immediately below the histogram. You map pixels to black (or the darkest Output Levels value) by entering a number from 0 to 255 in the first option box or by dragging the black slider triangle. For example, if you raise the value to 50, all colors with brightness values of 50 or less in the original image become black, darkening the image as shown in the first example of Figure 17-23.

Figure 17-23: The results of raising the first Input Levels value to 50 (left), lowering the last value to 200 (middle), and combining the two (right).

You can map pixels at the opposite end of the brightness scale to white (or the lightest Output Levels value) by entering a number from 0 to 255 in the last option box or by dragging the white slider triangle. If you lower the value to 200, all colors with brightness values of 200 or greater become white, lightening the image, as shown in the second example of Figure 17-23. In the last example of the figure, I raised the first value and lowered the last value, thereby increasing the amount of contrast in the image.

Gamma: The middle Input Levels option box and the corresponding gray triangle in the slider bar (shown highlighted in Figure 17-24) represent the mid- tone, or gamma value, which is the brightness level of the medium-gray value in the image. The gamma value can range from 0.10 to 9.99, with 1.00 being dead-on medium gray. Increase the gamma value or drag the gray slider triangle to the left to lighten the medium grays (also called midtones), as in the first and second examples of Figure 17-25. Lower the gamma value or drag the gray triangle to the right to darken the medium grays, as in the last example in the figure.

Figure 17-24: To create the spotlighting effects you see here, I selected the circular areas, inversed the selection, and applied the values shown in this very dialog box.

Figure 17-25: The results of raising (left and middle) and lowering (right) the gamma value to lighten the midtones in an image and darken them, respectively.

You can edit the gamma value also by pressing the up and down arrow keys. Pressing an arrow key changes the value by 0.01; pressing Shift+arrow changes the value by 0.10. I can’t stress enough how useful this technique is. I rarely do anything except press arrow keys in the Levels dialog box anymore.

Output Levels: Use these options to curtail the range of brightness levels in an image by lightening the darkest pixels and darkening the lightest pixels. You adjust the brightness of the darkest pixels — those that correspond to the black Input Levels slider triangle — by entering a number from 0 to 255 in the first option box or by dragging the black slider triangle. For example, if you raise the value to 100, no color can be darker than that brightness level (roughly 60-percent black), which lightens the image as shown in the first example of Figure 17-26. You adjust the brightness of the lightest pixels — those that correspond to the white Input Levels slider triangle — by entering a number from 0 to 255 in the second option box or by dragging the white slider triangle. If you lower the value to 175, no color can be lighter than that brightness level (roughly 30-percent black), darkening the image as shown in the second example of Figure 17-26. In the last example of the figure, I raised the first value and lowered the second value, thereby dramatically decreasing the amount of contrast in the image. Note that any change to the Output Levels values will decrease the contrast of the image.

Figure 17-26: The result of raising the first Output Levels value to 100 (left), lowering the second value to 175 (middle), and combining the two (right).

You can fully or partially invert an image using the Output Levels slider triangles. Just drag the black triangle to the right and drag the white triangle to the left past the black triangle. The colors flip, whites mapping to dark colors and blacks mapping to light colors.

Load and Save: You can load settings to disk and save settings to disk using these buttons.

Auto: You might assume that the Auto button in the Levels dialog box performs the same function as the Auto Levels command, discussed earlier in this chapter. And if you were working in a version of the program before Photoshop 7, you’d be right. Photoshop 7, however, added the Options button into the mix. Since then, the effect of clicking Auto in the Levels dialog box (as well as in the Curves dialog box) has depended on the settings in the Auto Color Correction Options dialog box, described next.

Options: Clicking the Options button in the Levels (or Curves) dialog box brings up the Auto Color Correction Options dialog box, shown in Figure 17-27. The top section, Algorithms, determines the type of correction you want to apply. Instead of the long, somewhat confusing names, these three choices could be labeled Auto Contrast, Auto Levels, and Auto Color, because that’s what the choices are equivalent to. In fact, you can rest your cursor over each name to see an informative tool tip telling you just this. Turn on the Snap Neutral Midtones check box and you’ll apply Auto Color’s automatic gamma correction as well. If you select the Save as Defaults check box, your settings will be remembered the next time you use the Auto button in the Levels and Curves dialog boxes.

Figure 17-27: Customizing the settings in the Auto Color Correction Options dialog box lets you take the “auto” out of Photoshop’s auto correction commands.

The Target Colors & Clipping settings come into play not only when you click the Auto button in the Levels and Curves dialog boxes but also when you choose the Auto Levels and Auto Contrast commands in the Adjustments sub- menu. (This is assuming that Save as Defaults is selected.) Here you can choose colors to assign to the target values for the highlights, midtones, and shadows in your image. You also have access to the Clip values for the highlights and shadows. Enter higher values to increase the number of pixels mapped to black and white; decrease the values to lessen the effect. Figure 17-28 compares the effect of the default 0.50 percent values to higher values of3.50 and 9.99 percent. As you can see, raising the Clip value produces higher contrast effects.

Figure 17-28: The effect of the default Clip values in the Auto Color Correction Options dialog box (left) and the effect after raising the values (middle and right).

Eyedroppers: Select one of the eyedropper tools in the Levels dialog box and click a pixel in the image window to automatically adjust the color of that pixel. If you click a pixel with the black eyedropper tool (the first of the three), Photoshop maps the color of the pixel and all darker colors to black. If you click a pixel with the white eyedropper tool (the last of the three), Photoshop maps it and all lighter colors to white. Use the gray eyedropper tool (middle) to change the color you clicked to medium gray and adjust all other colors accordingly. For example, if you click a light pixel, all light pixels change to medium gray and all other pixels change to even darker colors.

To give you a sense of how the Levels command works, the following steps describe how to improve the appearance of a low-contrast, shadow-heavy image, such as the first example in Color Plate 17-6. Luckily, you can bring out the highlights using Levels.

STEPS: Correcting Brightness and Contrast with the Levels Command

Press Ctrl+L (Win) or z -L (Mac) to display the Levels dialog box. As illustrated in the first example in Color Plate 17-6, most of the colors for this image are clustered on the left side of the histogram, showing that there are far more dark colors than light.

Press Ctrl+1 (Win) or z -1 (Mac) to examine the red channel. Assuming that you’re editing an RGB image, Ctrl+1 (z -1 on the Mac) displays a histogram for the red channel. The channel-specific histograms appear inset into the images in Color Plate 17-6.

Edit the black Input Levels value as needed. Drag the black slider triangle to below the point at which the histogram begins. In my case, there’s not much going on in the histogram until the point that’s below the “I” in the word “Input.” I dragged the black triangle to the beginning of the spike, changing the first Input Levels value to 16, as you can see in the red histogram in the second example of Color Plate 17-6.

Edit the white Input Levels value. Drag the white slider triangle to below the point at which the histogram ends. I have a lot farther to drag on the right side of the histogram than I did on the left. As seen in the second example of the color plate, I dragged the white slider triangle to the endpoint of the last peak of the histogram.

Edit the gamma value. Drag the gray triangle to the gravitational center of the histogram. Imagine that the histogram is a big mass, and you’re trying to balance the mass evenly on top of the gray triangle. If the histogram is weighted too heavily to the left, drag the gray triangle to the left. In the case of the red channel, I thought the histogram was pretty well balanced, so I left the gamma alone. Looking below to the green channel, however, you can see that I dragged toward the left a little bit, changing the gamma value to 1.10.

Repeat Steps 2 through 5 for the green and blue channels. Ctrl+2 (Win) or z -2 (Mac) takes you to the green channel; Ctrl+3 (Win) or z -3 (Mac) takes you to blue. At this point, your image probably has a preponderance of red about it. To correct this, you need to edit the green and blue channels in kind. The graphs in the third and fourth examples of Color Plate 17-6 show how I edited my histograms. Feel free to switch back and forth between channels as much as you like to get everything just right.

Press Ctrl+tilde (Win) or z -tilde (Mac) to return to the composite RGB histogram. After you get the color balance right, you can switch back to the composite mode and further edit the Input Levels. I sometimes bump up the gamma a few notches to account for dot gain.

You may notice that your RGB histogram has changed. Although the histograms in the individual color channels remain fixed, the composite histogram updates to reflect the red, green, and blue modifications. The final RGB histogram for my image is inset into the bottom example of Color Plate 17-6. As you can see, the colors are well distributed across the brightness range.

Press Enter (Win) or Return (Mac) to apply your changes. Just for fun, press Ctrl+Z (Win) or z -Z (Mac) a few times to see the before and after shots. Quite the transformation, eh?

The Curves command

If you want to be able to map any brightness value in an image to absolutely any other brightness value — no holds barred, as they say — you want the Curves command. When you choose Image Adjustments Curves or press Ctrl+M (z -M on the Mac), Photoshop displays the Curves dialog box, shown in Figure 17-29, which offers access to the most complex and powerful color correction options on the planet.

Figure 17-29: The Curves dialog box lets you distribute brightness values by adjusting the curves on a graph.

Quickly, here’s how the options work:

Channel: Surely you know how this option works by now. You select the color channel that you want to edit from this pop-up menu. You can apply different mapping functions to different channels by drawing in the graph below the pop-up menu. But, as is always the case, the options along the right side of the dialog box affect all colors in the selected portion of an image regardless of which Channel option is active.

Brightness graph: The brightness graph is where you map brightness values in the original image to new brightness values. The horizontal axis of the graph represents input levels; the vertical axis represents output levels. The brightness curve charts the relationship between input and output levels. The lower-left corner is the origin of the graph (the point at which both input and output values are 0). Move right in the graph for higher input values and up for higher output values. Because the brightness graph is the core of this dialog box, upcoming sections explain it in more detail.

Brightness bar: The horizontal brightness bar shows the direction of light and dark values in the graph. When the dark end of the brightness bar appears on the left — as by default when editing an RGB image — colors are measured in terms of brightness values. The colors in the graph proceed from black on the left to white on the right, as demonstrated in the left example of Figure 17-30. Therefore, higher values produce lighter colors. This is my preferred setting because it measures colors in the same direction as the Levels dialog box.

Figure 17-30: Click the brightness bar to change the way in which the graph measures color: by brightness values (left) or by ink coverage (right).

If you click the brightness bar, white and black switch places, as shown in the second example of the figure. The result is that Photoshop measures the colors in terms of ink coverage, from 0 to 100 percent of the primary color. Higher values now produce darker colors. This is the default setting for grayscale and CMYK images.

Curve tools: Use the curve tools to draw the curve in the brightness graph. The point tool (labeled in Figure 17-31) is selected by default. Click in the graph with this tool to add a point to the curve. Drag a point to move it. To delete a point, Ctrl-click (Win) or z -click (Mac) it.

Figure 17-31: Use the pencil tool to draw free-form lines in the brightness graph. If the lines appear rough, you can soften them by clicking the Smooth button.

The pencil tool lets you draw free-form curves simply by dragging in the graph, as illustrated in Figure 17-31. This pencil works much like Photoshop’s standard pencil tool. This means you can draw straight lines by clicking one location in the graph and Shift-clicking a different point.

Input and Output values: The Input and Output values monitor the location of your cursor in the graph according to brightness values or ink coverage, depending on the setting of the brightness bar. You can modify the Input and Output values when working with the point tool. Just click the point on the graph that you want to adjust and then enter new values. The Input number represents the brightness or ink value of the point before you entered the Curves dialog box; the Output number represents the new brightness or ink value.

When editing multiple graph points from the keyboard, it’s helpful to be able to activate the points from the keyboard as well. To advance from one point to the next, press Ctrl+Tab (Control-Tab on the Mac). To select the previous point, press Ctrl+Shift+Tab (Control-Shift-Tab on the Mac). To deselect all points, press Ctrl+D (Win) or z -D (Mac).

Load and Save: Use these buttons to load and save settings to disk, respectively.

Smooth: Click the Smooth button to smooth out curves drawn with the pencil tool. Doing so leads to smoother color transitions in the image window. This button is dimmed except when you use the pencil tool.

Auto: This button is identical to the Auto button available in the Levels dialog box. For details, see “The Levels command” section earlier in this chapter.

Options: Identical to the Options button in the Levels dialog box, this is also covered in “The Levels command” section.

Eyedroppers: If you move the cursor out of the dialog box and into the image window, you get the standard eyedropper cursor. Click a pixel in the image to locate the brightness value of that pixel in the graph. A circle appears in the graph, and the Input and Output numbers list the value for as long as you hold down the mouse button, as shown in the first example in Figure 17-32.

Figure 17-32: Use the standard eyedropper cursor to locate a color in the brightness graph (left). Click with one of the eyedropper tools from the Curves dialog box to map the color of that pixel in the graph (middle). You then can edit the location of the point in the graph by dragging it (right).

The other eyedroppers work as they do in the Levels dialog box, mapping pixels to black, medium gray, or white (or other colors if you double-click the eyedropper icons). For example, the second image in Figure 17-32 shows the white eyedropper tool clicking on a light pixel, thereby mapping that value to white, as shown in the graph below the image.

To add a color as a point along the Curves graph, Ctrl-click (Win) or z -click (Mac) a pixel in the image window. Photoshop adds the point to the channel displayed in the dialog box. For example, if the RGB composite channel is visible, the point is added to the RGB composite curve. If the Red channel is visible, Photoshop adds the point to the red graph and leaves the green and blue graphs unchanged.

To add a color to all graphs, regardless of which channel is visible in the Curves dialog box, Ctrl+Shift-click (Win) or z -Shift-click (Mac) a pixel in the image window. In the case of an RGB image, Photoshop maps the red, green, and blue brightness values for that pixel to each of the red, green, and blue graphs in the Curves dialog box. The RGB composite graph shows no change — switch to the individual channels to see the new point.

Gradient maps

The Gradient Map command permits you to apply a gradation as a Curves map. In other words, you can use a gradient map to adjust the brightness values of an image to match the values in a custom gradient. Just choose Image AdjustmentsGradient Map to display the dialog box pictured in Figure 17-33. Make sure the Preview check box is turned on. Then click the down-pointing arrowhead to the right of the gradient preview to display the familiar gradient drop-down palette. Select a gradient other than Foreground to Background and watch the fireworks.

Figure 17-33: Choose the Gradient Map command to apply a preset gradient as a Curves map. Color Plate 17-7 shows examples.

In the first row of Color Plate 17-7, I applied a couple of gradient maps to the original image on the left. The Chrome map had jagged edges, which inspired me to apply Gaussian Blur to it and a couple other Gradient Map variations in the middle row. In the bottom row, I mixed these fantastic images with their underlying originals using the Color blend mode.

What’s going on? As foreign as it may sound, any gradient can be expressed as a Curves graph, progressing through a variety of brightness values in each of the three (RGB) or four (CMYK) color channels. When applied as a gradient map, the beginning of the gradient maps black; the end of the gradient maps white. If you apply the Violet, Orange preset, for example, the dark colors in the image map to violet and the light colors map to orange. Noise-type gradients (introduced in the “Applying Gradient Fills” section of Chapter 6) produce especially interesting effects.

Practical applications: Continuous curves

When you first enter the Curves dialog box, the brightness curve appears as a straight line strung between two points, as shown in the first example of Figure 17-34, mapping every input level from black (the lower-left point) to white (the upper-right point) to an identical output level. If you want to perform seamless color corrections, the point tool is your best bet because it enables you to edit the levels in the brightness graph while maintaining a continuous curve.

Figure 17-34: Create a single point in the curve with the point tool (left) and then drag it upward (middle) to lighten the image evenly or downward (right) to or darken it evenly.

To lighten the colors, click near the middle of the curve with the point tool to create a new point and then drag the point upward, as demonstrated in the second example of Figure 17-34. To darken the image, drag the point downward, as in the third example.

Create two points in the curve to boost or lessen the contrast between colors in the image. In the first example of Figure 17-35, I created one point very near the white point in the curve and another point very close to the black point. I then dragged down on the left point and up on the right point to make the dark pixels darker and the light pixels lighter, which translates to higher contrast.

Figure 17-35: Create two points in the curve to change the appearance of contrast in an image, whether by increasing it mildly (left), decreasing it (middle), or boosting it dramatically (right).

In the second example of the figure, I did just the opposite, dragging up on the left point to lighten the dark pixels and down on the right point to darken the light pixels. As you can see in the second image, this lessens the contrast between colors, making the image more gray.

In the final example of Figure 17-35, I bolstered the contrast with a vengeance by dragging the right point down and to the left. This has the effect of springing the right half of the curve farther upward, thus increasing the brightness of the light pixels in the image.

Practical applications: Arbitrary curves

You can create some mind-numbing color variations by adjusting the brightness curve arbitrarily, mapping light pixels to dark, dark pixels to light, and in-between pixels all over the place. In the first example of Figure 17-36, I used the point tool to achieve an arbitrary curve. By dragging the left point severely upward and the right point severely downward, I caused dark and light pixels alike to soar across the spectrum.

Figure 17-36: These arbitrary brightness curves were created using the point tool (left) and the pencil tool (right).

If you’re interested in something a little more subtle, try applying an arbitrary curve to a single channel in a color image. Color Plate 17-8, for example, shows an image subject to relatively basic color manipulations in the green and blue channels, followed by an arbitrary adjustment to the red channel.

Although you can certainly achieve arbitrary effects using the point tool, the pencil tool is more versatile and less inhibiting. As shown in the last example of Figure 17-36, I created an effect that would alarm Carlos Castaneda just by zigzagging my way across the graph and clicking the Smooth button.

In fact, the Smooth button is an integral part of using the pencil tool. Try this little experiment: Draw a bunch of random lines and squiggles with the pencil tool in the brightness graph. As shown in the first example of Figure 17-37, your efforts will most likely yield an unspeakably hideous and utterly unrecognizable effect.

Figure 17-37: After drawing a series of random lines with the pencil tool (left), I clicked the Smooth button once to connect the lines into a frenetic curve (middle) and then twice more to even out the curve, thus preserving more of the original image (right).

Next, click the Smooth button. Photoshop automatically connects all portions of the curve, miraculously smoothing out the color-mapping effect and rescuing some semblance of your image, as shown in the second example in the figure. If the effect is still too radical, you can continue to smooth it by clicking the Smooth button additional times. I clicked the button twice more to create the right image in Figure 17-37. Eventually, the Smooth button restores the curve to a straight line.

The Shadow/Highlight command

The lens on a digital camera is an astonishing thing, but in certain areas it just doesn’t hold a candle to the good old human eye. Every waking moment of every day, for instance, the irises in our eyes are constantly making adjustments to determine the amount of light that gets in so we can perceive as much as possible. Modern cameras try their best to keep up with complicated and varied lighting situations, but you’re often stuck having to choose between sacrificing the darker areas of an image or overexposing the lighter areas. For example, how many times have you photographed someone against the sky, only to find the sky perfectly exposed and your subject darker than the gothic poetry of a troubled teen?

The Shadow/Highlight command examines the image and, according to your settings, deems certain spots to be “shadows” and others “highlights.” From there, you adjust the sliders to tell Photoshop just how much brightening or darkening it should perform on those areas. It’s a smart feature that’s deceptively easy to master. The first two sections of the dialog box, Shadows and Highlights, contain identically named sliders. Naturally, the Shadows section controls the lightening of shadows in an image, and the Highlights section controls the darkening of brighter areas. Here’s a list of the options available in both sections:

Amount: In the Shadows section, the Amount slider lets you specify the degree to which the shadows in an image will be lightened. In the Highlights section, the slider controls how much the highlights will be darkened. A value of 0 percent yields no change in the image; a value of 100 percent results in maximum brightening of the shadows (in the Shadows section) or darkening of the highlights (in the Highlights section). The default Shadows Amount setting of 50 percent is a safe place to start when lightening shadows in an image.

Tonal Width: This setting adjusts the range of the pixels that get modified by the command. In the Shadows section, higher values increase the range of shadow areas that gets lightened and lower values concentrate on only the darker regions of the image. In the Highlights section, higher values increase the range of light areas that gets darkened and lower values restrict the adjustment to only the lighter regions. The default Tonal Width value in both sections is 50 percent. If you find that the command is lightening too much of an image, lower the value in the Shadows section to correct it.

Radius: The Shadow/Highlight command determines which areas are shadows and which are highlights by examining each pixel compared to the pixels that surround it. This prevents every stray dark pixel from being classified as a shadow and subsequently lightened, for example. Adjust the Radius sliders to determine the size of each pixel’s neighborhood, or in other words, the number of surrounding pixels that are taken into account when each pixel is categorized as shadow or highlight.

Radius is the setting you’ll most likely need to adjust on an image-by-image basis. The default setting of 30 pixels is good place to start, but keep in mind that by increasing the Radius value you apply a less exacting change to the image, and by decreasing the value you lose some of the contrast.

Below the Shadows and Highlights sections is a third area labeled Adjustments. It contains the following options:

Color Correction: Occasionally, the Shadow/Highlight command can make the colors in an image a little less vivid. The Color Correction slider lets you adjust the saturation of the color in the affected portion of the image. In grayscale images, this option is replaced with a general Brightness setting.

Midtone Contrast: This setting is fairly self-explanatory. It increases or decreases the contrast of the midtone pixels in the image. Generally speaking, higher values mean a darker image and lower values produce a lighter, more even result.

Black Clip and White Clip: These values let you adjust the maximum settings for how dark the adjusted shadow pixels will be and how light the adjusted highlight pixels will be. While the limit for both values is 50 percent, I advise you to never even approach that high a value. On the contrary; keep these settings as low as you can to provide for smooth transitions and healthy contrast levels in your images.

The Shadow/Highlight dialog box lets you save your settings and then load them later using the Save and Load buttons on the right. If you want to designate your current settings as the default for the command, click the Save As Defaults button at the bottom of the dialog box. Finally, click the Show More Options check box to toggle between the default reduced view, which gives you access to only the two Amount sliders, and the expanded view, which presents you with all the options we just discussed.

Figure 17-39 shows an image of what appears to be some sort of security officer in one of those avant-garde French prisons we read about so often. The original image (on the left) is a nicely composed shot that has been marred by the brightness of the sky in the background, which caused the camera’s iris to close and render the subject all but noir, as they say. To create the middle image, I applied the Shadow/ Highlight command with the default settings, which do a pretty great job of pulling light back into the shadows without harming the brightness or detail in the surrounding sky. In the final image on the right, I cranked up the Shadows Amount to 75 and the Tonal Width to 60. For this image, that’s about as far as I can go without starting to degrade the image quality.

Figure 17-39: The Shadow/Highlight command does an expert job of recovering the detail in this man’s face and costume. On second thought, perhaps I should have left him as he was.