Hue, Saturation, and Lightness

When we see people trying to make skin tones less red or skies less purple with Curves, we have to roll our eyes and bite our tongues, which is uncomfortable to say the least! The best tool for addressing issues with hue and saturation is, believe it or not, the Hue/Saturation feature.

However, Hue/Saturation is a tad more mysterious than Levels and Curves for at least three reasons.

  • The relationship between the controls and the numbers that represent the image is much less obvious than with Levels and Curves.

  • Much of the power of Hue/Saturation is hiddenyou have to dig to find it.

  • Unlike Levels and Curves, which are global adjustments (though we'll show you how to turn them into local ones in Chapter 7, The Digital Darkroom), Hue/Saturation is at heart a localized correction tool.

But Hue/Saturation isn't hard to master, and once you've done so, you'll find it's indispensible. The basic Hue/Saturation dialog box appears deceptively simplesee Figure 6-50.

Figure 6-50. The Master panel of the Hue/Saturation dialog box

Unfortunately, the Master panel of Hue/Saturation is of limited use. It does provides one of many ways of converting color images to grayscale (just reduce the Saturation slider all the way down to -100); it lets you produce colorized versions of color images using the Colorize checkbox; and it lets you produce "postcard" color by boosting saturation with the Saturation slider. The real power is hidden a little deeper, but let's deal with Colorize first.


Figure 6-51 shows various treatments of an image with Colorize. The appearance is similar to a duotone, but the images are color images, and editable as suchyou can run Hue/Saturation only on color images, while you can create duotones only from grayscale ones.

Figure 6-51. Colorize

You can use Colorize for fast-and-dirty simulations of sepiatones, cyanotypes, selenotypes, bromide prints, and the like, as well as creating images that were impossible by traditional darkroom methods.

When the Colorize checkbox is checked, the Hue slider sets the dominant hue (the number is the hue angle, the same as the Hue field in the Color Picker); the Saturation slider sets the saturation on a scale from 0 to 100, with 0 being grayscale (completely unsaturated) and 100 being fully saturated; and the Lightness slider lets you darken or lighten the image on a scale of -100 to 100, with the default center point at zero. If you experiment, you'll find that the same settings produce different results depending on both the color mode (RGB, CMYK, or Lab), and the specific RGB or CMYK color space.

The Master Panel Controls

When the Colorize checkbox is disabled, the Lightness slider's behavior doesn't change, but that of the Hue and Saturation sliders does.

The Hue slider

The Hue slider shifts all the colors in the image by the specified hue angle. Small shifts are sometimes useful, but shifting hue by more than 5 or so degrees usually produces effects that can charitably be described as "creative"see Figure 6-52. The top color bar shows the original color, the bottom color bar shifts to show the resulting color.

Figure 6-52. Master Hue slider

Global hue shifts are rarely useful except for creative effects (for which they can be quite useful), so we rarely use the Master Hue sliderinstead, we adjust the hue of individual colors (see the next section, "The Color Panel Controls").

The Saturation slider

As with the Hue slider, the master Saturation slider is more chainsaw than scalpel. Boosting the Master Saturation value can work in small doses, but it's easy to drive your color into postcard territory (which is fine if you're in the postcard business)see Figure 6-53.

Figure 6-53. Master Saturation slider

We're much more likely to adjust the hue and saturation of individual color ranges separately (which we'll show you how to do shortly), because with the Master panel sliders, when we get one color right, we've typically pushed another too far, and yet another not far enough.

We also, on occasion, use the Master Saturation slider to convert color images to grayscalePhotoshop offers half-a-zillion ways to do this, and they all produce subtly different resultssee "The Color of Grayscale" in Chapter 12, Essential Image Techniques.

Figure 6-54 shows the same image converted to grayscale by choosing Grayscale from the Mode submenu (under the Image menu) and by adjusting the master saturation to -100. Note that the result you get from desaturating varies depending on which RGB or CMYK color space the original color image lived in.

Figure 6-54. Converting to grayscale by mode change versus by desaturating

The Lightness slider

We never use the Master panel's Lightness sliderit works exactly like the Brightness slider in Brightness and Contrast, simply shifting all the values, and usually clipping either highlights or shadows as a result. We do use it for individual color panels, however; see below.

The Color Panel Controls

The real power of Hue/Saturation is inside the individual color panels. When you open the Edit menu in the Hue/Saturation dialog box, you can choose Reds, Yellows, Greens, Cyans, Blues, or Magentas. At first glance, the controls offered in the individual color panels may seem identical to those in the Master panelthere's a Hue slider, a Saturation slider, and a Lightness slider. These work the same way as the Master panel's sliders, only they're constrained to operating on the selected color. What's much less obvious is that the named color ranges are simply preset starting points that you can adjust to affect exactly the color range you want. The controls operate the same way in all the other color panelsthe only difference between the panels is the menu name and the preset range of color they affect.

The non-obvious controls are at the bottom of the dialog box. In between the two color bars are two inner vertical sliders and two outer triangular sliders. These define the range of color affected by the sliders (see Figure 6-55).

Figure 6-55. Color panels and color range controls

For additional feedback, the numbers above the color bar show you the hue angles of the four slider positions. You can adjust the range of color that's fully affected by dragging the dark gray bar between the inner sliders, or by adjusting the inner sliders individually, and you can adjust the "feather"the range of colors that's partially affectedby dragging the outer sliders.

You can also adjust the range by selecting the three eyedropper tools located above the color bars by clicking them in the image. The left eyedropper centers the range of fully affected colors on the hue of the pixel on which you click; the center eyedropper (with the plus sign) extends the range of fully selected colors to include the hue of the pixel on which you clicked; and the right eyedropper (with the minus sign) excludes the hue of the pixel on which you clicked from the fully affected range of colors. The size of the feather doesn't change with the eyedroppers, but it moves as the fully affected color range expands and contracts. Essentially, the controls provide a color-range selection with a controllable feather. The following two tips make using these controls a great deal easier.

Tip: Use Modifier Keys with the Eyedropper

We never go to the bother of choosing the different eyedropper tools. The left eyedropper is always selected by default. To use it to expand the color range, simply Shift-click; to eliminate colors from the color range, Option-click. The modifiers are just temporary overridesthey don't actually switch the selected toolso you can just use them when you need them.

Tip: Use the Hue Slider for Visual Feedback

The biggest problem with the color range controls is that they don't provide any visual feedback as to which colors are affected. A simple trick lets you see clearly the range of selected colorsmove the Hue slider all the way to the right or left before you start adjusting the color range sliders, then set it back to zero once you've adjusted the range (see Figure 6-56).

Figure 6-56. Adjusting the color range controls

It's a very simple trick, but an invaluable one. It makes it easy to target the exact range of colors you want to tweak rather than the preset ranges Photoshop offers.

It's also worth noting that the preset ranges are simply arbitrary labels. There's nothing to prevent you from tweaking six different ranges of reds, or greens, or yellowsthough we find we rarely need more than three.

Skin tone adjustments

Hue/Saturation is invaluable for adjusting skin tones. It's a great deal easier to adjust the red-yellow balance of Caucasian skin with the Hue slider than it is to do so with Curvesin Curves you usually have to adjust all three color curves to obtain the correct hue, where the Hue slider lets you do so in a single move.

Figure 6-57 shows an image of Bruce shot by our friend and colleague Jeff Schewe. The unusally ruddy skin tones were likely caused by the excellent bottle of 1978 Masi Amarone we'd just consumed with dinner.

Figure 6-57. A skin tone problem

Jeff insists that Bruce looks "particularly Scottish" in this image. But while Bruce is proud to be a Scot, he is reluctant to be thought a sot. So we'll use Hue/Saturation to make his complexion a little less florid.

Making these kinds of adjustments with Curves is akin to medieval torture! In RGB, you'd have to manipulate at least two, and probably all three color curves plus the composite, and you'd probably have to bounce back and forth between the individual curves several times, since each move affects the others. In CMYK, a curve edit is even more complex since you have four color channels plus the composite rather than than three.

Hue/Saturation is useful in both RGB and in CMYK, but it lends itself to much finer adjustments in CMYK than in RGB. In RGB, it manipulates light, while in CMYK it manipulates ink percentages. Those of you with sharp eyes will have noticed that we made the edits to this image in RGB with CMYK soft-proofing turned on.

When we're preparing images for a CMYK destination, we always soft-proof, especially on Hue/Saturation adjustments, but even with good output profiles and a well-calibrated display, we're likely to make small adjustments after conversion to CMYK, though we try to get as close as possible to the desired result in RGB. When we looked at proofs of the final results from Figure 6-58, we felt that the skin tone was just a hair too yellow-green. Figure 6-59 shows the image after CMYK correction, along with the correction itself.

Figure 6-58. Skin tone adjustments

Figure 6-59. Hue/Saturation correction in CMYK

Matching hues

Another common task for which Hue/Saturation is well suited is matching hues across images. The light may change during an event, or you may simply have to force two disparate images to match.

Figure 6-60 shows a typical hue-matching challenge. Bruce stumbled across this wedding procession in La Paz, Bolivia, and had to switch from slide to color negative film halfway through. (The lack of oxygen at the 13,000-foot altitude made it somewhat miraculous that he managed to load any kind of film in the camera!)

Figure 6-60. Matching hues

The red shirts are rendered as a magenta-red by one film stock and as an orange-red by the other. And just to make things a little more challenging, one image is in ProPhoto RGB, the other is in Colormatch RGB, so the RGB numbers are of little help. Fortunately, the Info palette lets us display Lab values, so we'll use these as a guideon a well-calibrated system you can make the match by eye, but the numbers always provide a useful reality check, and Lab numbers act as a universal translator, letting you match colors in different color spaces, or even different color modes.

While Photoshop's Adjustment submenu offers a command labeled "Match Colors," we confess that we've yet to find a way to make it produce predictable results, though it can make for some interesting creative effects. Hue/Saturation is quick and controllable.

Gamut mapping

One further task for which we rely on Hue/Saturation is gamut-mappingcontrolling the rendering of colors present in the source image that are outside the gamut of the output process. In theory, perceptual rendering is supposed to take care of this for you. In practice, though, it sometimes fails. All profile-creation tools make assumptions, almost invariably undocumented, about the source space they attempt to map into the gamut of the device being profiled, and when the source space doesn't match the undocumented assumption, you can wind up with solid blobs of saturated color.

Sometimes the fix is as simple as just desaturating the color while looking at a soft-proofed version of the image. In other cases, you may be able to improve the rendering by adjusting hue and/or lightness too. You have to make the fix before converting to the output space, because after the conversion is done, all you can do is make the blobs more or less saturatedyou can't recover the differences that represented detail.

We can't show you the out-of-gamut RGB colors in this book, because the CMYK print process won't let us. What we can do is to show you the unadjusted profile conversions of some problem images, the fixes we applied, and the results.

Figure 6-61 shows some problem images. The unadjusted versions are darn close to what we saw in the soft proofs that alerted us to the potential problems. In all these instances, somethinghue, lightness, or saturationhas to give. There's an element of subjectivity in these decisionswe can't get the color we really want, so we have to settle for something else. There's no objectively correct answer as to what that something else is, but in all three cases, we feel that our choices are improvements over the straight, unadjusted profile conversions.

Figure 6-61. Gamut problems

Figure 6-62 shows the adjusted images, along with the Hue/Saturation moves we used to make them. Only one of the examplesthe red shirts in the last imagewas fixed by a simple desaturation. The other fixes all involved changes to lightness and to hue, and in some cases the hue and lightness moves allowed us to boost saturation rather than decrease it.

Figure 6-62. Gamut fixes

Printing blues with CMYK inks is always tricky, because CMYK spaces contain so few of them! In most other color ranges, desaturation is our first line of defense for out-of-gamut colors. However, in the blue regions, lightness moves are often more effective, as shown in the middle image in Figure 6-62.

Tip: Color Picker's Gamut Warning

Photoshop's Gamut Warning (it lives on the View menupress Command-Shift-Y) isn't something we find terribly useful on images. It shows us which RGB or Lab colors are outside the gamut of our CMYK working space, but it doesn't show how far out of gamut they are, nor does it show us where the nearest in-gamut colors lie.

However, if you turn on the Gamut Warning while you're in the Color Picker, you can see exactly where the gamut boundary lies at different hue angles and lightnesssee Figure 6-63.

Figure 6-63. Gamut Warning in the Color Picker

Bear in mind that the Gamut Warning always shows you the gamut of your current CMYK working spacesee "CMYK Working Space" in Chapter 5, Color Settingsso make sure that you have the correct CMYK profile loaded before you try to use this tip!

Other Methods

Levels, Curves, and Hue/Saturation are the fundamental tools for adjusting global tone and color (we'll show you to apply them as selective local adjustments in Chapter 7, The Digital Darkroom). But several of the other commands on the Adjustments submenu are extremely useful, albeit in fewer situations.

You must master Levels, Curves, and Hue/Saturation to consider yourself any kind of Photoshop user. But the more specialized toolsto which the remainder of this chapter is devotedcan save you time and let you produce better-quality work, which is, after all, the object of the whole exercise. Photoshop always offers multiple ways to do just about anything, but one way is usually better or faster than the others.

Real World Adobe Photoshop CS2(c) Industrial-Strength Production Techniques
Real World Adobe Photoshop CS2: Industrial-strength Production Techniques
ISBN: B000N7B9T6
Year: 2006
Pages: 220
Authors: Bruce Fraser © 2008-2017.
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