Adobe has taken the Vibrance adjustment that was only available in Adobe Camera Raw and incorporated it into Photoshop CS4. It is available both as a direct adjustment (via the Image>Adjustments menu) and as an Adjustment Layer.
When you adjust an image using the new Vibrance adjustment, you’ll be presenting with two sliders: Vibrance and Saturation.
The Saturation slider is the same as the one you’ll find in the Hue/Saturation dialog box. Moving it toward the left will make your image less colorful, while moving it to the right will make your image more colorful.
The problem with the Saturation slider is that it treats all colors equally. That means one color can easily become overly saturated before another reaches its full potential. Just think about a photograph of a flower. If you were to increase the saturation of the entire image, you might oversaturate the flower before the brown soil it’s planted in becomes as colorful as you desire. If you push the Saturation slider until the soil reaches its full potential, the much more colorful flower will become oversaturated and look artificial. When an area becomes oversaturated, it starts to lose detail, which is known as Saturation Clipping.
This adjustment was invented in an effort to prevent saturation clipping. The Vibrance slider works just like the Saturation slider in that it makes your image more or less colorful. The difference is that the Vibrance slider will boost the saturation of the areas that are not all that colorful a lot more than the areas that are already colorful. If you think back to our flower example, increasing the Vibrance would make the soil much more colorful while only affecting the flower a small amount.
The Vibrance slider also attempts to prevent skin tones from becoming overly colorful (which might cause people to look sunburned).
For the reasons stated above, many people have completely replaced the Saturation slider with the Vibrance slider. I suggest you use them together in the following ways:
Exaggerate Mellow Colors: If you want the not-so-colorful areas of your image to stand out, consider lowering the Saturation setting while increasing the Vibrance setting. On some images, I’ll even crank the Vibrance slider all the way to the right and then lower the Saturation slider until the image doesn’t look overly colorful.
Tone Down Mellow Colors: Sometimes you’ll want the most colorful areas to be center stage and not be distracted by surrounding elements. That’s when I’ll move the Vibrance slider down quite a bit (sometimes all the way to -100) and then adjust the Saturation slider until the more colorful areas within the image look appropriate.Most of the time I use one of the above approaches and simply don’t take it to the extreme I’ve shown in these examples.