The Secondary Curves Explained

The secondary curves are a deceptively powerful set of controls that allow you to make very small or large adjustments to the hue, saturation, and luminance of an image based solely on regions of hue that you specify using control points on a curve.

Important: Curves cannot be animated with keyframes, although just about every other parameter in the Secondaries room can be.

These curves work much differently than the curves controls of the Primary In room. Each of the secondary curves controls defaults to a flat horizontal line running halfway through the graph area.

Figure. Secondary curves.

The visible spectrum is represented along the surface of the curve by a wrap-around gradient, the ends of which wrap around to the other side of the curve. The control points at the left and right of this curve are linked, so that moving one moves the other, to ensure a smooth transition if you make any adjustments to red, which wraps around the end of the curve.

Tip: If you’re having a hard time identifying the portion of curve that affects the part of the image you want to adjust, you can use the color swatches in the 3D scopes to sample a pixel from the preview, and a horizontal indicator will show the point on the curve that corresponds to the sampled value. For more information, see Sampling Color for Analysis.

Adding points to the surface of this curve lets you define regions of hue that you want to adjust. Raising the curve in these regions increases the value of the particular aspect of color that’s modified by a specific curve, while lowering the curve decreases the value.

Figure. Secondary curves with control points.

For example, if you add four control points to the Saturation curve to lower the green-through-blue range of the curve, you can smoothly desaturate everything that’s blue and green throughout the frame, while leaving all other colors intact.

Figure. Before and after adding 4 points to the Secondary Sat curve.

One of the nicest aspects of these controls is that they allow for extremely specific adjustments to narrow or wide areas of color, with exceptionally smooth transitions from the corrected to the uncorrected areas of the image. In many instances, the results may be smoother than might be achievable with the HSL qualifiers.

Another key advantage these controls have over the HSL qualifiers is that you can make simultaneous adjustments to noncontiguous ranges of hue. In other words, you can boost or lower values in the red, green, and blue areas of an image while minimizing the effect of this adjustment on the yellow, cyan, and magenta portions of the image.

Figure. Adding multiple control points to a secondary curve.

The secondary curves use B-Splines, just like the primary curves controls. In fact, you add and edit control points on the secondary curves in exactly the same way. For more information, see Curve Editing Control Points and B-Splines.

Important: Adjustments made using the secondary curves cannot be limited using the vignette or HSL controls.

Using the Secondary Curves

This section provides examples of how to use each of the three kinds of secondary curves.

Important: Curves cannot be animated with keyframes, although just about every other parameter in the Secondaries room can be.

The Hue Curve Tab

When you raise or lower part of the secondary Hue curve, you make a hue adjustment similar to the one you make when you use the Global Hue control, except that you only rotate the hue value for the selected range of hue specified by the curve. Raising the curve shifts the values toward red, while lowering the curve shifts the values toward blue.

Figure. Before and after a secondary Hue curve adjustment.

This control can be valuable for making narrow, shallow adjustments to the reddish/orange section of the spectrum that affects skin tones, in order to quickly and smoothly add or remove warmth.

The Sat Curve Tab

Raising the Saturation curve increases the saturation in that portion of the spectrum, while lowering it decreases the saturation. This is a powerful tool for creating stylized looks that enhance or subdue specific colors throughout the frame.

Figure. Before and after a secondary Sat curve adjustment.

The Lum Curve Tab

Raising the Luminance curve lightens the colors in that portion of the spectrum, while lowering it darkens them. This is a good tool to use when you need to make contrast adjustments to specific regions of color.

Figure. Before and after a secondary lum curve adjustment.