Curves

From Photoshop
Revision as of 15:26, 20 January 2012 by WikiSysopPS (talk | contribs) (Multiplication? Say whu?)
Jump to: navigation, search

Curves is the master adjustment, one ring to rule them all etc. Learn Curves if you learn nothing else.

Heres the Curves window:

Curves 01.png

It looks like a graph because it is. It graphs the value range change that you impose upon the image. Here's how you read it.

Curves 03.png

The Curve above is its default state and represents no change. Below is a curve adjustments that represents a multiplation value of 0.5.

Curves 02.png

Multiplication? Say whu?

So... what is a multiplication? Well... they call it digital art because, at its root, it is derived from numbers. In the digital world black is 0 (zero) and white is 1 (one). The graph above can be read in the following manner:

  • If 1 is multiplied by 0.5 the result is 0.5.
  • If 0.5 is multiplied by 0.5 the result is 0.25
  • If 0 is multiplied by 0.5 (or indeed any other number) the result is 0.

So... color adjustments are mathematics. These maths are (for the most part) quiet simple.

I will drive this fact home with a small demo. In the image below the left half has had a layer of mid grey (50% brightness) placed above it and set to Multiplication Blend Mode. This will multiply the image by 0.5. The right half has had a 0.5 multiplication curve applied as an adjustment layer. As you can see, they are both identical.

Curves 04.png

Though its possible to be a digital artist without knowing too much about the underlying maths of what you are doing, I am telling you this for a reason: students often stab away at PS's color controls without knowing what they do. 'I just fiddle with them untilo it looks good' is what I often hear. Unless you know how you achieved your successes, then you will not be able to reproduce them.

Visualizing color operations

A good colorist will be able to visualize color operations not just through their effects upon the image, but in the shape of the curve. These shapes constitute 'thought forms' that are embodiments of their associated color edits.

Operation name AKA Nodes Thought form
Add Add, Grade, ColorCorrect, ColorLookup. Col add.png
Contrast S Shaped curve RolloffContrast, ColorCorrect, ColorLookup Col contrast.png
Gamma Gamma, Grade, ColorCorrect, ColorLookup Col gamma.png
Lift Offset Grade, ColorLookup Col lift.png
Multiply Gain, Brightness, Exposure Multiply, Grade, ColorCorrect, ColorLookup Col multiply.png
Clamp Clamp, ColorLookup Col clamp.png
Saturation Saturation, ColorCorrect Col sat.png
Arbitrary Color lookup, LUT ColorLookup, HueCorrect Col arbitrary.png