When you adjust color in digital images, several common—and often unintended—byproducts arise. Increase or decrease contrast, and saturation will rise or fall. Increase or decrease saturation, and lightness will change. Make a hue adjustment with Curves (or Levels) by targeting specific channels, and an image either will lighten or darken. Make a hue adjustment with Hue/Saturation, and both saturation and luminosity are likely to shift, sometimes lightening and other times darkening. Correct one problem, and you may create another. Sometimes these byproducts are desirable; usually, they’re not. While these changes may be minor, sometimes insignificant, when making subtle adjustments, they can become major when making more dramatic adjustments.
Is there a cure? There are several!
You can make additional adjustments to correct the byproducts of one adjustment. For instance, to compensate for value shifts when making color adjustments by targeting individual channels with Levels or Curves, many return to the Master channel to correct the accompanying shifts in value. To correct saturation shifts when contrast has been increased or decreased, a second adjustment is often made with Hue/Saturation.
Most of these secondary adjustments are performed to stabilize one color component while shifting another.
Color can be broken down into three essential elements: hue (a spectrum around the color wheel from red through yellow, green, blue, cyan, magenta and back to red); saturation (a gradient from intense to dull); and luminosity (a gradient from dark to light). Problematic color artifacts show up in one of these areas when adjusting others. That’s because the most common color modes (RGB and CMYK) have the hue, saturation and luminosity interconnected, so it’s necessary to make changes to more than one channel at a time.
In LAB mode, luminosity has its own separate channel and you can make adjustments to it alone, but saturation and hue are still wrapped into two channels, A and B. The color spaces that treat all three elements separately, HSB, HSL and HSV, aren’t supported by Photoshop (or Lightroom).
Some adjustment tools allow you to make adjustments to one component of color without affecting the others, and you should use these tools whenever it’s practical. You can check the Preserve Luminosity box when using Color Balance to set the brightness when making adjustments to hue. This works well when adjustments are made to the midtones, but when targeting highlights and/or shadows, brightness or contrast may shift. Tools like these build the solution for the problem directly into their interface, but these tools aren’t always the ones we need to accomplish a given task, nor are they the most precise.
Some tools even produce problems that aren’t curable. For example, increasing or decreasing value using the Lightness slider with Hue/Saturation will reduce an image’s dynamic range, making white or black gray while darkening or lightening. The best policy is to avoid using these tools altogether. You can do more and do it with greater precision using other tools. (In this specific case, use Curves.)
Blending Modes to the Rescue
Wouldn’t it be nice if you could target one specific component of color without affecting the others with any color adjustment tool? With a blending technique in Photoshop, you can. You can use the blending mode of adjustment layers to constrain the effects of an adjustment to one or more components of a color. If you’re making an adjustment directly to an image without using adjustment layers, you can Fade (Edit > Fade) the problem away immediately after applying the adjustment.
Unfortunately, you can’t do this during RAW conversion with either Lightroom or ACR. Many of these side effects are built into the behavior of the sliders and no additional blend mode feature exists.
You’ll find all of the blend modes in Photoshop’s Layers palette. All layers, including adjustment layers, have a blending mode. A layer can only have one blending mode, but a layer’s blending mode may be changed at anytime. The default is Normal, but there are many other modes to choose from. The long list of options you’ll find under the blending mode pull-down menu, offering 17 choices in all, may seem overwhelming at first and deter you from using them altogether. While some experimentation with all of the blending modes may prove fruitful, start with the four that are most useful for color adjustment, the four that target specific components of color: Hue, Saturation, Color and Luminosity.
You can use the adjustment layer blending modes of Hue, Saturation, Color and Luminosity to target single color components, regardless of which space you’re editing in. The blending mode of an adjustment layer constrains the effects of an adjustment to the component of color specified in its title.
Hue allows an adjustment layer to affect only hue, eliminating shifts in luminosity. Saturation allows an adjustment layer to affect only saturation, eliminating shifts in luminosity, and you can use this for most saturation adjustments, for instance, when you use Hue/Saturation.
Color allows an adjustment layer to affect both hue and saturation, eliminating shifts in luminosity. Use this for most hue adjustments, for instance, when you use a single channel in Curves.
Luminosity allows an adjustment layer to affect only value or brightness, eliminating shifts in saturation. Use this for most contrast adjustments, for instance, when you use the master channel in Curves. This functions just like adjusting the L channel in LAB without having to make a color mode conversion, possibly forcing you to flatten a file.
You can specify the blending mode of an adjustment layer when you first create it. Or, you can change the blending mode of an adjustment layer after its creation. Either way, it’s more than likely that you’ll want to compare the effects of both the alternate blending mode and the Normal blending mode. Sometimes, you may find you like the side effects and don’t want to remove them. In these cases, leave the blend mode on its default Normal. As a general rule, I recommend you use the blend mode that targets only the element of color you’re adjusting.
You can’t reduce a blending mode by a percentage; it’s an all-or-nothing proposition. If, for instance, you want to remove most, but not all, of the additional saturation introduced by a shift in contrast, you’ll need to choose either blending mode Normal or L
uminosity, and then make an additional Hue/Saturation adjustment. Pick the mode that gets you closest to the result you desire and then fine-tune the final effect with a subsequent adjustment.
The precision and degree of control over color you can acquire today is nothing short of astonishing. It’s responsible for producing a dramatic revolution in color photography. We now have near-total control of color’s three primary elements—hue, saturation and luminosity.
The precision and degree of control over color you can acquire today is nothing short of astonishing.
It’s responsible for producing a dramatic revolution in color photography. We now have near-total control of color’s three primary elements—hue, saturation and luminosity.
Add to this nonlinear color adjustment (even color transformation) the ability to affect specific hues without affecting others. Add to this the ability to make adjustments to specific ranges within each of those components, for instance, the saturation of highlights and/or shadows, rather than the component in its entirety. And there are many other possibilities. You can do virtually anything. You need only imagine the possibilities and then find the right tool for the job.
John Paul Caponigro, author of Adobe Photoshop Master Class and the video series R/Evolution, is an internationally renowned fine artist, an authority on digital printing, and a respected lecturer and workshop leader. Visit johnpaulcaponigro.com.