Depending on the viewpoint, conditions of illumination, and choice of camera or film, photographic images can have color cast. (Examples can be a bluish cast.) Improper settings of white balance or insufficient automatic color timing, color cast can occur even with digital cameras.
The aid of color correction or color timing can erase these color casts. Some photographers and image editors use color timing in order to purposefully add color casts to the pictures to emphasize certain emotions or feelings. Therefore, anyone who practises professional image editing must have knowledge of the potential of color correction.
Color correction can, thus, be defined as the retroactive adjustment or alteration of a photograph’s color effect. In a first step, the scanned or read in photographs are usually altered to a more natural appeal. After this process, the photograph should give the same impression that it had on the photographer at the moment it was taken. A starting point for this is white balance, provided by the software. White balance is also an option incorporated in contemporary cameras to avoid color cast from the outset. The editor simply has to find a pixel that represents the maximal white in the surrounding area. Professional photographers and image editors usually take along color charts. These charts can later be used to find the maximal white, black, or grey in the particular pictures.
Even under the best shooting conditions, color cast can still occur on the photographs. In these cases, image editing programs can be used for color correction. To initiate this process, the editor selects a pixel of maximal white and/or black. Professional editors even recognize and select pixels of medium grey and use these as starting points to initiate a color balance.
The result of this first process is a picture with a natural appearance. In a second step, image editors can make use of color timing to improve the expressiveness of the photograph. For this purpose, image editing programs include filters to intensify specific color effects in the picture. In many cases, the editor shifts the color range between the tonal values of red and yellow. This method is especially useful for skin tones and emphasizes the expressiveness of the pictures. Another option is to purposefully select a specific pixel that is not grey, but is supposed to appear grey after the process of color correction. This option results in a shift of tonal values that changes the expressiveness of the photograph.