Appearance of Surface Color
Several factors affect the appearance of surface color on a given surface. These include background (simultaneous color contrast), chromatic adaption (successive color contrast), color constancy, brightness, size and saturation.
Factors that Affect the Appearance of Surface Color
The visual effect of an object is strongly influenced by the colors behind it. The background color can have a profound effect on the perception of hue, saturation and brightness. A background can:
- Induce its complementary hue: Against a green background, an object will appear redder. Against a blue background, it will appear more orange. This effect is most noticeable when the background color is more saturated than the foreground color. Yellow is the color most strongly affected by its background; blue is the least affected. This effect is called “simultaneous color contrast.”
- Reduce the apparent saturation of a similar hue: For instance, a red background brings more green into the foreground object. A pink object will appear almost neutral. Generally, a highly saturated background color will desaturate objects of the same hue and enhance the saturation in objects with a complementary hue.
- Induce or reduce brightness: A dark background makes an object look brighter. A bright background makes an object look darker. This is called “simultaneous brightness contrast.”
- Produce assimilation effects: Assimilation is the opposite of simultaneous contrast. In this case, the background seems to spread to the object. For example, an image with white in the background will make the blue values look lighter, while having black in the background would make the same blue look darker. This is called “assimilation” of color or the “spreading effect.”
It’s also worth noting that these effects are less noticeable on a computer screen because it isn’t possible to create a truly saturated background (green in particular is very desaturated on a computer screen).
You may have seen optical illusions that have you stare at a color picture for a full minute and then look at a white wall. On the wall you see the image again, but with the colors reversed. This is an example of chromatic adaptation, which occurs when the viewer has prolonged exposure to light of a particular wavelength (color). The effect is called “successive brightness contrast” because the effects—while similar to simultaneous color contrast—take place over time rather than concurrently.
Chromatic adaptation can have several effects:
- Inducing the complementary color: As in our optical illusion example, looking for a long time at a red field would cause a pale or white object to then appear greenish. This is called a negative afterimage.
- Reducing apparent saturation: A red field would make a pink object look white.
- Inducing or reducing brightness: Looking at a bright field makes the next object you look at dimmer. Think of coming into a room after being out in bright sunshine. The room could be lit normally and it will still look dark to you for a moment. This is called “rapid light adaptation.”
Most objects retain their color when viewed in different light. This phenomenon would not be the case if wavelength alone determined the appearance of surface colors. For wavelengths of light to reach our eyes, two things need to happen:
- The light must fall on an object.
- The light must then be reflected from that object to our eye.
Different sources emit light with different spectral composition. The most common light sources are the sun, tungsten filament bulbs and fluorescent bulbs. Daylight is the most common light. It emits most wavelengths in equal amounts and changes as a function of time of day and weather conditions. Tungsten filament bulbs are balanced toward long (red) wavelengths and cast a warm-looking light. Fluorescent light has shorter (blue) wavelengths and casts cold-looking light. When looking at the same object in each of these three environments, the spectral composition of the light hitting an object and reflecting to the eye differs. This is confirmed by photography, which requires the use of special lights and filters to compensate for differences in the color of light.
But in daily life, we don’t really notice the difference. Our brains are used to taking in all this color information, as well as relationships between colors within our field of view. We adapt so well to the differences in light that we just don’t notice them in most circumstances. Your new green shirt may have looked slightly different in the fluorescent light of the store’s dressing room than in the tungsten light of your home, but it still looks green.
A color’s brightness is affected by several factors:
- Luminance: Light with more luminance or energy looks brighter.
- Spectral location: When luminance is equal, colors from the middle of the spectrum (green to yellow) appear brighter than red and blue.
- Background: Objects look brighter on a dark background and darker on a light background.
- Viewer’s adaptation: Light looks brighter when the viewer has adapted to a lower luminance level and vice versa.
- Duration: Brightness increases with duration, up to about 1/10 of a second, then it begins to decline. While it may seem counterintuitive, a short flash of the right duration seems brighter than a steady light of the same luminance.
We perceive hues as yellower and bluer at high brightness (called the Bezold-Brucke effect). But brightness does not affect color matches. That is, if you matched a 580 nm yellow by mixing red and green, they would continue to look identical even if the brightness increased.
Color is less distinct in smaller objects. Dark colors, such as blue, start to look black. Bright, desaturated colors, such as yellow, appear whiter.
Except for yellow and some blues, adding or subtracting white causes a shift in perceived hue (called the Abney effect). The direction of change varies with location in color space and is a complex topic, but designers should be aware that changing saturation also causes alterations in the perceived hue.