Sometimes you want to make an adjustment to your image almost everywhere. You could use the adjustment brush and paint almost everywhere, but that could be slow. Instead, make the adjustment everywhere, with a global change in the Basic panel, and then use the adjustment brush to change back the area you didn’t want to affect. This works in both Camera Raw and Lightroom. Here’s an example. I want to give this portrait image that glow that is popular these days, but I don’t want it to affect the eyes or the mouth.
I will give the image the glow by reducing clarity to -60 in the Basic panel. I also boosted contrast and vibrance.
With the adjustment brush set to +60 on clarity (the opposite of the global change I made), I would then paint over the eyes and mouth to reverse the negative clarity change. That is the idea — but to make the change obvious to you in this small image environment, I actually painted with +100 clarity, to accentuate the eyes even more:
Note that with this technique, Lightroom (or Camera Raw) isn’t blurring the eyes and mouth and then sharpening what it has blurred — that would not in fact work. It is only applying one change to these areas — the cumulative effect of the negative and positive clarity.
Another example of applying a change everywhere and then painting back with the opposite effect where you didn’t want it is an image that needs to be brighter almost everywhere — brighten it globally, then paint back the areas that you didn’t want brighter with negative brightness. Depending on what type of adjustment you are making, you may find that the amount that you need to paint back is not exactly the opposite of your global change … after you paint with the adjustment brush, adjust the slider until it looks good visually.
Finally, note that this will not work when you want part of your image in color and part in black and white — you can’t desaturate the image (saturation of -100) and then paint color back in with +100 saturation. In this case instead start with the color image, and with the adjustment brush set to -100 saturation, paint the areas that you want to be in black and white.