The chapter “Lightness, Brightness, Contrast and Constancy” offers us an interesting insight into normal visualization. For example, in a gray-scaled graph where the gray levels denote certain values or meanings. It is likely that our reading differs from place to place because how gray one pixel is is perceptually affected by the surrounding pixels. Another analogous example would be if you want to appear taller you stand with the shorter. Part of it looks like against graphical integrity. But mostly we do not even realize such effects (e.g. simultaneous contrast) are affecting our visualization. One solution to this problem would be using more than one visual variables. For instance, in a gray-scaled graph we can use texture (scattered vs. dense) to compensate for the effect we mentioned above.