Curve (tonality) explained

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.^{[1] [2]}

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.^[3]

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,^[4] but it can also be used in RGB, CMYK or whatever other colour models the software supports.

See also

• Blend modes
• Image histogram
• Hurter–Driffield curve
• Tone reproduction curve

External links

• Defanging the Curves Vampire, Dan Margulis, December, 1996

Notes and References

1. http://docs.gimp.org/en/gimp-tool-curves.html The gimp manual
2. http://www.adobe.com/designcenter/photoshop/articles/phscs2at_learncurves_02.html Adobe web site on curves in Photoshop
3. Detailed instructions on the usage of the 'curves' and 'levels' functionality of image editing software; PhotoshopEssentials.com
4. Book: Margulis, Dan. Dan Margulis

   . Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace. Dan Margulis. 0-321-35678-0. 2005.