Methods of image calibration and in particular of image calibration having a multiple of color scales as well as to quantitative imaging such as quantitative medical imaging, or to a display device or to a system for displaying an image, or to a controller of a display, or to software to enable the image calibration, or to a visualization application and a display. The method for processing an image, includes the steps of: —selecting at least one trajectory in a color space; —defining a transformation which primarily increases perceptual linearity of consecutive points belonging to the at least one trajectory; —applying the transformation to the image. This has the advantage that the perceptual linearity can be restricted to the trajectory.