In image editing

Image editing

Image editing encompasses the processes of altering images, whether they be digital photographs, traditional analog photographs, or illustrations. Traditional analog image editing is known as photo retouching, using tools such as an airbrush to modify photographs, or editing illustrations with any...

, a curve is a remapping of image tonality, specified as a function from input level to output level, used as a way to emphasize colours or other elements in a picture.

Curves can usually be applied to all channels together in an image, or to each channel individually.

Applying a curve to all channels typically changes the brightness in part of the spectrum. The software user may for example make light parts of a picture lighter and dark parts darker to increase contrast.

Applying a curve to individual channels can be used to stress a colour. This is particularly efficient in the Lab color space

Lab color space

A Lab color space is a color-opponent space with dimension L for lightness and a and b for the color-opponent dimensions, based on nonlinearly compressed CIE XYZ color space coordinates....

 due to the separation of luminance

Luminance

Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...

 and chromaticity

Chromaticity

Chromaticity is an objective specification of the quality of a color regardless of its luminance, that is, as determined by its hue and colorfulness ....

, but it can also be used in RGB

RGB color model

The RGB color model is an additive color model in which red, green, and blue light is added together in various ways to reproduce a broad array of colors...

, CMYK

CMYK color model

The CMYK color model is a subtractive color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four inks used in some color printing: cyan, magenta, yellow, and key...

 or whatever other color models the software supports.

External links

• Defanging the Curves Vampire, Dan Margulis
  Dan Margulis
  Dan Margulis is an expert on color correction and reproduction of photographs, using Adobe Photoshop or similar software.His Professional Photoshop series is widely viewed as an authoritative work in the field of digital color correction of photographs...
  
  , December, 1996