- See the Wikipedia article at Color correction.
Color correction is the process of applying adjustments to an image to resolve variations in lighting and viewing conditions. It is an essential subject of study for photography and video.
Human sight is a dynamic process, taking many factors into account. The perception of contrast and motion is more significant than the perception of color, and thus many color-related issues are taken for granted so that the brain can concentrate on other facets of vision.
Different sources of light are stronger in certain ranges of color than others. In general, they can be arranged along an axis from blue to amber, correlating to what is called color temperature. The daylit sky casts a strong blue light on objects, while incandescent bulbs and fire emit amber light. Human vision tends to ignore these differences in the "white point" of light.
Meanwhile, film and digital image sensors are less forgiving when it comes to color. What is known to be a white sheet of paper can appear in most any shade depending on the light source. Color correction reduces such distractions in an image, allowing that piece of paper to appear white when viewed or printed. Optical devices such as colored gel filters can be used to correct color. When an image is digitized, software algorithms are applied.
Color correction in Photoshop
Until the addition of the Lab color mode in version 3.0, color correction was limited to use of the Color Balance adjustment. This was often a matter of trial-and-error.
In Lab color mode, Color Balance can be used to manipulate the b channel, which happens to be the blue/amber axis. (The "Tint" adjustment that often adjusts green/magenta balance in televisions can be achieved by altering the a channel.)
Later adjustments such as Variations and Photo Filter allow color corrections to be done effectively in other color modes.
Version 7.0.1 added the Camera RAW tool, giving Photoshop users more effective editing of RAW format images, including color correction. A separate program called Adobe Lightroom was eventually created to deal with RAW images.