1. A method for generating a set of color-toning curves, the method comprising: receiving a first set of color-toning parameters for shadow regions, a second set of color-toning parameters for highlight regions, and an invariance property which needs to be maintained during color toning; computing a set of color-toning-curve values and a set of color-toning-curve slopes using the first set of color-toning parameters, the second set of color-toning parameters, and the invariance property; and generating the set of color-toning curves using the set of color-toning-curve values and the set of color-toning-curve slopes.