“Saturation” sounds like what you do to yourself with a bag of Cheetos and an X-Files marathon on cable but, in Photoshop or a similar application, saturation can be described as the “pureness” of a color, where a highly saturated image looks full of color and a less-saturated image appears washed out. Saturation works together with Hue and Brightness to form the HSB color model.
Bold and Subtle
The hue of an image is the actual color in question—is it red, yellow, blue or a combination thereof? Saturation is the purity of that color, along what might be described as a “dull-to-normal-to-vivid” spectrum. Brightness is the intensity of the color—this is the one you’ve probably fiddled with the most. But brightness doesn’t always solve an image’s problem the way that hue and saturation can.
In your software, changing the hue changes the actual color in your image. That’s not something you’ll generally do except to make either subtle changes, such as to compensate Bold and Subtle for a sickly skin tone—or bold changes, such as to completely stylize the image with unnatural colors. (Think Warhol.) If you’ve got people coming up a little yellow or greenish, you can tap the Hue slider a bit in your software (in Photoshop it’s Image > Adjust Hue/Saturation) to make subtle changes. If you need to change them from skin tone to a fairly deep green, you can do that, too. Just slide away.
Altering the saturation of an image can have wonderful results for the overall effect of that image. The key is that increasing saturation can cause the rich colors in an image to become more vivid while the more tame colors—tans, whites, light skin tones—will stay a little closer to the original. The results: ruby red lips or vivid striped clothes or a deep blue car body with richly tinted windows. Likewise, Bold and Subtle decreasing saturation can be handy for making an image appear closer to black and white, or look like it was taken on a rainy day, or for a “colorized” effect where part of the image seem black-and-white and other parts seem to have just a little color, like an aging color photo.
Too much saturation can look fake—usually 5-20% will boost a photo nicely if that photo didn’t start too washed out. Even more saturation than that can sometimes rescue a poorly shot image (or an image from a digital camera or scanner with bad color reproduction) and give it a little visual zing.