Frequently Asked Questions

Why do some of the Curves Adjustment Layers use Normal Mode while others use Luminosity Mode?

The reasoning behind using Normal vs. Luminosity Mode stems from the type of adjustment desired at each step in the Tone System. One of the strengths of the Tone System is that, as you progress through each step, the next step (if correctly applied) will have as little impact on the previous adjustments as possible. It is impossible for each step to have no effect on the preceding adjustments. By using Normal Mode for steps where the desired outcome is a color adjustment and Luminosity Mode for density and contrast adjustments, you can reduce unintended interference between steps. We use Normal Mode for White Point, Color Cast, and Vibrance Adjustments since they are related to adjusting the color in the image. The White Point adjustment is intended to adjust both the color (by neutralizing the white point) and the tonal range (by setting the point where the very first or lightest ink is deposited on the paper). Color Cast adjusts the color by setting a neutral midpoint value to true neutral. The Vibrance layer adjusts the purity of the color.

By applying the Black Point (See page on Reflected Color), Density, and Contrast adjustments in Luminosity Mode, we affect the image's tonal range while leaving the colors as unchanged as possible. The Black Point setting defines the first separation of shadow value from the absolute black the paper/ink/printer combination allows. It would seem that the Black Point could be set in Normal Mode. The issue with shadows is that they are not illuminated by the Sun but by reflected light—the sky in most cases. This means the color of shadows is not neutral; it is often shifted toward blue/cyan hues by light reflecting from the sky. By setting the Black Point in Luminosity Mode, we avoid shifting shadow values away from their natural color balance. This does not necessarily apply to images made indoors or in a studio. In those cases, you could use Luminosity Mode for the Black Point adjustment.

Why adjust only two channels when performing a cast correction (step 5)?

When you adjust two colors, you are adjusting all three colors. Remember that the colors function in complementary pairs — RGB and CMY. For example, if you remove red, you are also adding cyan. Since red is made of equal amounts of yellow and magenta, you are adjusting yellow and magenta, and therefore blue and green as well. If you adjust all three color channels, adjusting the third color channel will undo some of the correction you made with the first two color channel adjustments.