halo : Gamut mapping of an original color image may produce unwanted artifacts in the rendered image. One such artifact is referred to as a halo. Halo artifacts occur near edges of objects in the rendered image, and are a consequence of using spatially dependent gamut mapping algorithms to map an original color image onto a constrained color space.其实是给edge增加一些影子，光的信息
gradient reversal:Gradient reversals are gradients that after manipulating the image, change their direction
shock: The region quickly evolves into a step-wise discontinuity with infinite gradient and zero
conductance known as a “shock.”