2003-2006 Mike Russell, All Rights Reserved

An Anthology of Curve Moves

"We like to call them Hat Moves, not Tricks" - Bill Irwin

We've all heard of the "S" curve, but can you name any other curve shapes? This is what I'm talking about. It's high time we curve folks had some names for the various curve shapes, or moves that we use. This document takes a stab at a vocabulary for discussing what curves look like, as well as the intent behind each curve shape.

 
Curve Name
Discussion
Boost
The Boost consists of a is a common contrast enhancing move that consists of moving both endpoints toward the middle. It is most often the result of setting the shadow or highlight.
Dog Leg

This curve is most commonly used on either the a or b curves of Lab mode. It is useful for controlling the saturation of the individual yellow, blue, green, or magenta components of those curves.

For example, green foliage may be intensified by dog-legging both the yellow and green quadrants of the a and b channels in Lab mode.

To facilitate this curve, use the Pin Grid commands to lock the appropriate corner of the curve in place.

Drop
The Drop simply "drops" the midtone slightly without changing the endpoints. It changes overall darkness when applied to all channels, or color balance and overall brightness in the midtones when applied to fewer channels.
S
The S curve increases contrast in the midtones, and reduces contrast in the shadow and highlight. It resembles the response curve of film in that light and dark detail is compressed, rather than cut off as with the Boost.
Inverted S
The Inverted S increases contrast in the shadows and highlights, and decreases it in the midtones. This relatively unusual curve is used for images that have detail in the extreme light and dark areas, but none in the mid tones. An example would be a picture of a polar bear in a snow storm eating a chocolate ice cream cone.
Raise
The Raise bumps up the mid tones and leaves the end points alone. Like the Drop, it may be used for either overall brightness increase (when used on all channels affecting brightness, or with the master curve), or color balance.
Inversion
The Inversion inverts the image, creating a negative image from a positive, or vice versa.
Half Inversion, or Pyramid

This move is commonly used with either the a or b channel in Lab mode, to dramatically change half the colors controlled by that channel, and leave the other colors alone. For example, this curve turns magenta to green, and retains green objects.

Come to think of it, there's an inverted version of this curve, shaped like the letter V; let's call that curve the V, or Inverted Pyramid.

To facilitate this move, use the Pin Grid command to lock the appropriate corner in place.

High Shoulder

High Shoulder is half of an S curve. It is used to increase shadow detail while compressing highlights without losing them completely.

This is a good curve for under-exposed images.

The Curve Library's Fine Screen curves provide variations on this curve.

Lizard Tail

Lizard tail is a very small and sharp upturn or downturn at the end of a curve, normally used to rescue or otherwise emphasize shadow or highlight detail that is in danger of being lost. Two large and shallow lizard tails are an inverted S.

Low Shoulder

Low Shoulder is half of an S curve. It increases midtone and highlight detail without completely sacrificing shadow detail.

This is a good curve for over-exposed images.

The Curve Library's Fine Multiply curves provide variations on this curve.

Veil

The veil is named not for its shape, but for the effect it has on the image. Blacks and whites become gray when this curve is applied to the master curve, the L curve in in Lab, or the B curve in HSB.

When used on the a or b curves of Lab, the veil decreases saturation.

Local Boost

Local Boost is used to increase the contrast or color content of a particular object's tonal range. In this case, the segment near the pointer will receive a boost in magenta contrast.

This is a very important move supporting the enhancement of color, color contrast, and overall contrast. As the old adage says, "what goes up must come down", so for every Local Boost there are one or more Local Veils created. The trick is to make these veils land on objects, such as the background, that don't matter. In this case, the diagonal reference line was used to distribute the veil equally on either side of the boosted region.

Straight Boost

This is a combination of Boost and Lift, and is used in color correction. Straight Lift is especially appropriate when the image is too dark.

Straight Lift created in two steps. First do a Boost, as when creating a neutral point. Then move the highlight end of the curve toward the middle, straightening the curve.

Straight Drop
Straight Drop, like Straight Lift is a color correction move that is appropriate when the overall image is too light. It is applied at the endpoint, to straighten the curve after the middle point is added as part of a color correction move.
Specialized curves  
Sabattier, or Solarizing Curve

This is an unusual curve named after a film process called the "Sabattier Effect", or solarization. It is generally used only for surreal effects.

Note: This is one of the few curves containing a negative slope. To accomplish this curve, uncheck the CurveGuard option.



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