Observation Skills and CG - An Introduction to Computer Graphics for Artists - page 44

3.3.1.1 White-Balancing

In general, color observations are best made in fl at, gray light such as is available
outdoors on a day that is overcast with high clouds. This causes rays to be scattered
at the same time as they are diminished in intensity. The result is a lack of cast shad-
ows and highlights. The colors that remain are lit well enough to be evaluated with-
out being so bright that they lose saturation or so dark that their hues are not easily
discerned. When this kind of lighting is not available, colors must be white- balanced .
To white balance an image, a pixel is sampled from an area that should be white,
like a white card photographed in the scene as reference, and then the color of the
card is subtracted from the entire image. This strips the image of color contamina-
tion from the light source.
After you have a white balanced image, you will have to fi nd a part of the refer-
ence that is the best average of the saturation, luminosity, and hue of the colors you
want. This will sometimes be a color that can be sampled from the image, but not
always. Keep in mind that the colors in a photograph are usually wrong unless
expertly taken. They will provide a good impression of the differences between
colors, but will not tell you the correct raw values.

3.3.2 Optical Illusions

If a reference object is not examined carefully, some of its details can be hidden by
any optical illusions that may be present. For instance, a bag of the Cheetos brand
snack food appears to use a background gradient that transitions from orange to yel-
low. Instead of a gradient, the background is made from only two unmixed colors,
yellow and orange. On the top of the bag, large orange circles are arranged in a
perfectly straight row. In the gaps between the circles, small dots of yellow are vis-
ible. As the rows of orange circles descend down the surface of the bag, they become
progressively smaller, until the bottom of the bag has become completely yellow.
The illusion of a smooth gradient is caused by the same optical color mixing that
French Impressionist painters used to make the colors in their paintings more vibrant
in the late nineteenth century (Fig. 3.3 ).
Another type of illusion is caused when a complex surface appears to be covered
with repeated structures, as in the abstract 3D decorations found in mosques. If the
parts of an apparently symmetrical structure are slightly modifi ed from one piece to
the next, it is possible to create a unique non-repeating pattern that appears to repeat
in a regular pattern. If one tries to build such an object without noting how the pieces
have been transformed relative to each other, it will be impossible to make the
pieces fi t together properly (Fig. 3.4 ).
This is mentioned to emphasize the importance of carefully studying any subject
you intend to build as a 3D object. You may think you understand the structure or
color of an object, but if you don't double-check your observations, may fi nd you
were mistaken.