While working on luma, you can modify the R, G, B, saturation, and luma along the luma range.

You can toggle the Red, Green, Blue, Saturation, and Luma buttons to activate their corresponding curves. Manipulate the shape of each curve over the luma range that you want to affect. The value of the parameter that corresponds with the curve changes relative to the height of the point on the curve in the curve editing area.

Each curve is a hue gradient and as the shape of the curve changes, the colors along the curve's gradient change to reflect the result. For example:

• Raising the blue curve over the darker luma range, the curve along that range becomes bluer (for all pixels with a lower mean luma value, the blue channel value increases—the result in the image is that blue is added to the shadows)
• Lowering the saturation curve over the lighter luma range, the saturation curve over that range desaturates (for all pixels with a higher mean-luma value, the saturation value decreases—the result in the image is that highlights wash out).