BrushCue contains two tools that appear to do the same thing: the Exposure Adjustment and the Brightness Adjustment tools. This post will explain the difference between the two. In doing so, we will learn a bit about color modifications in image editing workflows.
How Exposure Adjustments Work
An exposure adjustment is simpler to implement technically, so let's start there. As you probably know, digital cameras and displays work by using R, G, and B colors. R, G, and B correspond to the amount of red, green, and blue light. The exposure adjustment simply multiplies each component by a factor. This has a similar effect to changing the exposure duration on a camera.
How Brightness Adjustments Work
The Brightness Adjust tool has an intermediate step: it converts the color to OkLab, adjusts the lightness, then converts back to RGB. If you have read other posts of mine, you probably know where this is going. OkLab is a perceptual color space, which means equal steps in OkLab are meant to feel like equal steps to the human eye. Doing the adjustment in OkLab lets us change brightness more uniformly across different hues.
When you would use each
If you want to make a scene lighter or darker for aesthetic purposes, use Brightness Adjust. Because it works in OkLab, the change tends to look more even across colors and better matches how we perceive lightness.
Exposure Adjust still has a place. It behaves like a camera exposure change, so it is useful when you want a more “photographic” effect or you are matching exposure changes elsewhere in a pipeline. It is also simple and predictable in linear RGB, which can be helpful for technical tweaks.