1. An image processing method, comprising: converting input image data from a source color space to a target color space, the target color space having a color component corresponding to brightness that is orthogonal to other color components of the target color space; converting the brightness component of the image data from a linear representation to a perceptual representation; altering the converted brightness component of the image data according to control parameters derived from viewing conditions of an output device; converting the altered brightness component of the image data from the perceptual representation to a linear representation; and converting the image data to a color space of the output device.