Curve (tonality)

[[File:Curves none applied.png|thumb|300px|right|Photo and curve dialog in the GIMP ]]

thumb|300px|right|Photo and curve dialog with red colour emphasized in the lighter end of the spectrum.

In image editing, 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.<ref>[http://docs.gimp.org/en/gimp-tool-curves.html The gimp manual]</ref><ref>[http://www.adobe.com/designcenter/photoshop/articles/phscs2at_learncurves_02.html Adobe web site on curves in Photoshop]</ref>

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. Light parts of a picture can be easily made lighter and dark parts darker to increase contrast.<ref>Detailed [http://www.photoshopessentials.com/photo-editing/levels-curves/ instructions] on the usage of the 'curves' and 'levels' functionality of image editing software; PhotoshopEssentials.com</ref>

Applying a curve to individual channels can be used to stress a colour. This is particularly efficient in the Lab colour space due to the separation of luminance and chromaticity,<ref>{{cite book|title=Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace|authorlink=Dan Margulis|first=Dan|last=Margulis|isbn=0-321-35678-0|year=2005|publisher=Peachpit Press }}</ref> but it can also be used in RGB, CMYK or whatever other colour models the software supports.

==References== {{reflist}}

==External links== * [http://www.ledet.com/margulis/Makeready/MA21-Defanging.pdf Defanging the Curves Vampire], Dan Margulis, December, 1996

Category:Digital photography Category:Image processing