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Color scale

Several of the coloring methods, including `Beta', `Charge', and `Occupancy', describe a range of floating point values rather than a set of names. These are colored via the color scale, which is a list of 1024 smoothly changing colors. There are many color gradations available. All of them consist of transformations of three colors. For instance, ``RGB'' colors the smallest value red, values near the middle of the scale are green, and the largest values are blue. Colors in-between are linear mixes of the two colors. The list of available gradations is given below.


Table 5.4: Available Color Scale Gradations.
Method Description
RGB small=red, middle=green, large=blue
BGR small=blue, middle=green, large=red
RWB small=red, middle=white, large=blue
BWR small=blue, middle=white, large=red
RWG small=red, middle=white, large=green
GWR small=green, middle=white, large=red
GWB small=green, middle=white, large=blue
BWG small=blue, middle=white, large=green
BlkW small=black, large=white
WBlk small=white, large=black


The minimum of the range of values is linearly scaled and shifted to start at 0 and end at 1. Assume the color scale is RGB. For a given value of x in the scale range [0..1], the RGB value is found first from a linear scaling based on the midpoint. If x $=$ 0, R is 1 (for maximum red). This continues linearly until x $=$ midpoint, at which point, R is 0 and stays 0. The green component is 0 at both x $=$ 0 and x $=$ 1 and is 1 at the midpoint. Linear scaling occurs in between. The blue component is 0 for x $<=$ midpoint, and 1 for x $=$ 1.

Figure 5.1: RGB color scale: the three plots shows the contributions of each color, and the resulting colors are on the bottom.
\begin{figure}\begin{center} \par \par \latex{ \scalebox{0.625}{\includegraphics{pictures/ug_color_scale}} } \end{center} \end{figure}

An additional term, ``min'', is added to each of the component terms before they are merged. This shifts the final colors more towards white or black. Min can take on values from -1 to 1.

Figure 5.2: The shift to the red component of the RGB scale caused by the value of ``min''.
\begin{figure}\begin{center} \par \par \latex{ \scalebox{0.625}{\includegraphics{pictures/ug_color_scale_min}} } \end{center} \end{figure}

There is only one color scale used at a time so it is impossible to display objects colored by multiple different color scales.

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Next: Materials Up: Coloring Methods Previous: Coloring by color categories   Contents   Index
vmd@ks.uiuc.edu