Exploration One: Visual Illusions, Part B The painting above, "Voices in the Sunset," has very little applied color. That is, if you saw these mixtures of paint puddle out of context, you would think them all mostly neutral. Put side by side in a painting, using the information you're about to read, and it looks like it has a lot of color doesn't it? We will spend one session of the upcoming workshop to explore this theory.
Before proceeding, you may want to print out the previous post (same name as this one but Part A) and keep the definitions part handy while reading this.
The process of color information by our visual system seems to operate in three successive stages:
- Trichromatic image capture: color information is recorded by the responses of the cone cells in the retina.
- Opponent processing: responses from the cones are converted into three signals, for brightness (value), yellowness vs. blueness, and redness vs. greeness. The latter two providing our perception of hue and saturation.
- Processing for color constancy: information on changes in hue, value, and saturation across the visual field is analyzed and resolved into an interpretation of the hue, value, and chroma of the visible surfaces.
Step #3 is the most interesting for us in this post. The brain decodes the visual input and then scans all of the data for variation, not for absolute data. We see always by comparisons. That is, variation in color is what gives meaning to visual input.
Stop here and go to this visual illusion by R. Beau Lotto, or visit www.lottolab.org. The blue tiles on the left cube and the yellow tiles on the right cube are actually the same.
The human visual system is not very good at being a physical light meter, but that is not its purpose. The important task is to break the image information down into meaningful components, and thereby perceive the nature of objects in view. This method of visual input has developed in humans to make us efficient see-ers. For example: relative "brightness" (remember that is the perceived intensity of value, hue, and chroma all rolled into one) is thought to be used by the brain to process motion, form, and texture!! WOW!
- The brightness of equally intense stimuli changes with their relative saturation and with shifts in hue. Under consistent light conditions...
- More saturated (pure) colors appear brighter than less saturated colors (i.e. strongly colored stimuli appear brighter than grey stimuli). Okay... that was an easy one.
- Red and blue colors appear brighter than yellow and green colors. (The reason that often times in the distant landscape you can still see the violet hues, but no the yellow and green).
This is likely to be an adaptive solution that evolved within the human eye and visual cortex to help identify more reflective surfaces (which are more saturated and would need to stand out in an environment of vegetation).
- However, the retina has a lower sensitivity to short wavelengths (blues). Therefore, a neutralized yellow may be perceived brighter than a pure blue.
- In general, contrast enhances the difference in brightness and/or color between interacting areas of an image. Such contrast effects are mutual, but if the surrounding area is larger and more intense than the area it encloses, then the contrast is correspondingly out of balance. (Think, light holes coming through trees here).
- Because the brain does not read visual stimuli in absolute terms (like an objective measuring device, sending raw light and color data to the brain), there can be failures of color constancy (see #3 above). The visual appearance of a surface color can be influenced by adjacent and interspersed colors respectively. Here are some samples of simultaneous contrast illusions.
- Simultaneous contrast of lightness: Patterns of moderate contrast appear to have more contrast in a low-contrast contest. Vice-versa, the same pattern appears to have less contrast in a high-contrast context. Think about this and how, let's say, the appearance of contrast between painting a sunset painting and painting a "dusk" painting are different in the way we would handle the contrasted areas with those areas similar in value.
- Simultaneous contrast of hue and chroma: A purplish-red color looks more purple against red, more red against purple, lower in chroma against bright purple-red, and progressively higher in chroma against dull red-purple, grey, and green. Just read that a few times and think of how you use analogous colors and neutrals in your own paintings to, as the galleries tend to say these days, give your painting more "punch."
- Simultaneous contrast of lightness and chroma: The same purple-red looks darker against a lighter, and lighter against a darker color of similar hue and chroma. Don't over think that one. You know it; you've just never written it in words before.
- Simultaneous contrast of hue: When a medium grey is seen against a background of similar value hue, the appearance of the color moves toward the hue of the additive complement. For example, the medium-grey figure against a red background shifts the perceived red background toward cyan.
Stop here and drool over Sorolla's "Desnudo de mujer" . See how easily the skin tones turned toward green when painted next to the pink satin.
- An important special case of simultaneous contrast of hue is the phenomenon of complementary colors in shadows. When we have a strongly-colored main light and a neutral secondary light source, the colors in the shadow of the main light shift in appearance toward the complementary color of the light. (Do not confuse this phenomenon with the hobby painter's recipe of adding the complementary pigment of the color of the object to get its color in shadow). The induced complementary effect is the basis of the artists' conventional rule (you know how much I hate rules) of warm lights creating cool shadows and vice versa.
Simultaneous contrast is responsible for the well-known artists problem that paint mixtures look quite different on the palette (especially a white palette) to their appearance on the painting. Experience and a growing capacity to see colors independent of their context can help here. The strategies of using a colored (that is stained) ground closer to the tonal level of the finished painting than a stark white, or of covering the canvas at an early stage with a mosaic of flat colors* can both minimize problems caused by simultaneous contrast on canvas. The colors in any painting have a fixed relationship to each other, and it is the business of the painter to get these relationships right. *Kevin Macpherson states in his second book, "Landscape Painting, Inside and Out," that he often mixes his colors for a painting on a canvas panel. Once the panel-palette is dried, he sometimes uses that mosaic of colors as the foundation for a painting.
Hang in there... one more point for today... Assimilation (reverse contrast) is a phenomenon having the opposite effect to simultaneous contrast, and is seen when small areas of color are closely interspersed. Reds look more purple beside blues and more orange beside yellows. The lightness of white or the darkness of black may seem to spread into neighboring regions. Similarly, colors ma appear to spread into or become assimilated into neighboring areas. All such effects tend to make neighboring areas appear more alike, rather than to enhance their differences as in the more familiar simultaneous contrast, hence the term "reverse contrast."
The Op Art movement of the 60s featured painting and sculpture that exploited these optical effects to create perceptual ambiguity created by colored surfaces, and to suggest movement created by lines and patterns in black and white.