How shading works

First of all, I was totally amazed by how Livingstone breaks down the artistic dilemma of having to visually portray differences in luminance through art using tools that cannot even approximate the number of luminances in the natural world. Furthermore, our visual system cannot even signal the scope of these different luminances, so we must rely on center/surround organization that discriminates locally. Thus, we see the abrupt differences between how dark/light something is and its immediate surround. In order to achieve this effect in artwork, artists use chiaroscuro by creating subtle opposing gradations in luminance between foreground and background The very idea of creating an artistic representation of something that cannot be accurately produced, which is in turn seen through a visual system that cannot biologically handle that difference in luminance is fascinating (and quite vexing).

I also really liked Livingstone's discussion toward the end of the chapter on how color and luminance was stretched by modernist and impressionist painters such as Monet, Matisse, and Derain. These paintings seem visually accurate, however, because the luminance values create depth cues that are easily perceivable. There is something of a dissonance in these paintings, as one aspect seems entirely realistic whereas another is not readily comprehendible. For Monet, Livingstone posits that the colorblind Where system detects the overall shape and spatial organization that creates depth, though the low-luminance contrasts also keep the viewer from being able to clearly or immediately identify the objects (What system). In the Monet example here and in Derain's work, aspects of the What system may create expressive rather than realistic dimensions while preserving the (colorblind) accuracy of depth.