To ensure a Vibrance adjustment layer only affects a certain part of the picture, what should you do?

To ensure that a Vibrance adjustment layer only affects a specific part of the picture, using a pixel mask and painting with black is the most effective approach. A pixel mask allows for selective visibility of the adjustment layer. When you paint with black on the mask, it hides the effects of that layer in the areas where you apply the paint. Essentially, this technique enables you to control precisely which areas of the image will receive the adjustments—in this case, the Vibrance adjustments—while leaving other areas untouched.

This method provides a non-destructive way to apply changes, as the original image remains intact, and you can easily modify the mask if needed. It enhances the flexibility and creativity in editing since you can refine the adjustments dynamically.

The other methods, such as adjusting layer opacity or changing the blending mode, would affect the entire image rather than allowing for specific sections to be targeted. Applying a filter to the entire image would also not provide the same level of control, as it would apply the effect uniformly across the whole canvas. Hence, using a pixel mask is the best practice for targeted adjustments like Vibrance.