Frequently Asked Questions

Why do some of the Curves Adjustment Layers use Normal Mode and other use Luminosity Mode?

The reasoning behind using Normal vs Luminosity Mode stems from the type of adjustment desired in each step in the Tone System. One of the strengths of the Tone System is that as you progress through each step, the following step (if correctly applied) with have as little impact on the previous adjustments as possible. It is impossible for the each step to have no effect on the the preceding adjustments. By using Normal Mode for the steps where the desired outcome is a color adjustment and Luminosity Mode for density and contrast adjustment, you can reduce the amount of unintended interference with each step. 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 adjusting a neutral mid point value to true neutral. The Vibrance layer adjusts the purity o f the color.

By applying the Black Point, Density, and Contrast adjustments in the Luminosity Mode, we affect the tonal range of the image, but leave the colors as unchanged as possible. The Black Point setting sets the first separation of shadow value from the absolute black the paper/ink/printer combination allows. It would seems that the Black Point could be made in the 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, but it is often shaded towards the blue/cyan hues by the light reflecting from the sky. By setting the Black Point in Luminosity Mode, we avoid shifting the 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 only adjust 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 complement 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 too. If you adjust all three color channels, adjusting the third color channel will undo some of the correction you made with the first two colors channel adjustments.