Curve (tonality)

Photo and curve dialog in the GIMP

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.^[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. 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 due to the separation of luminance and chromaticity,^[3] but it can also be used in RGB, CMYK or whatever other color models the software supports.

See also

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

References

1. ^ The gimp manual
2. ^ Adobe web site on curves in Photoshop
3. ^ Margulis, Dan (2005). Photoshop LAB Color: The Canyon Conundrum and Other Adventures in the Most Powerful Colorspace. ISBN 0321356780. 

External links

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