Graphics Reference
In-Depth Information
both of which are different from
saturation
(for example, ranging from
vivid red to muted red to gray with a bit of red). Hue also has perceptual
connotations. For example, use red for hot, warning, or loss; blue for cold or
night; green for profit; and so on. Using color semantics can help the viewer
more quickly understand the representation. It is important to understand
a little about color because you can use color in three main ways to add
information to nodes or edges:
• Magnitude
• Positive and negative values
• Categories
Magnitude
Similar to node size, you can use color to show magnitudes (such as counts
or size) by using a
quantitative color scale
(also called a
sequential
color scale
). In this use of color, typically you define the color for the
lowest value and the highest value. The chosen color scale should vary
from a dark color to a light color over the range of values. People perceive
brightness of the color and will see patterns based on brightness. Therefore,
you should use a set of colors that vary in brightness in proportion to
the numeric values they represent. For this reason, you should not use
a “rainbow color scale,” because the brightness varies inconsistently, as
shown in
Figure 5-4
.
If you take away the hue (such as with a low-contrast
projector or a black-and-white hard copy), the variation in brightness across
the colors is very apparent.
Figure 5-4:
The rainbow color scale (left) does not consistently increase in
brightness, as shown in the grayscale image of the same rainbow color scale
(right).
Do not
use a rainbow color scale for magnitude.
Examples of good choices include simply varying from a dark hue to a bright
version of that same hue. Or, pick a dark color (such as blue) and a related
bright color (such as cyan).
Figure 5-5
shows an example.
