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<HEAD><TITLE>R Color</TITLE></HEAD>
<H2>Internal Color Representation</H2>
<BODY>
Internally, R uses a 24 bit color model; with 8 bits describing
the intensity of each of the primaries red, green and blue.
These bytes are interpreted as values in the range 0-255,
with 0 representing the lowest intensity and 255 the highest.
The bytes are stored in the most significant bytes of a 32-bit
integer as follows:
<LISTING>
        color = (red<<8)|(blue<<16)|(green<<24);
</LISTING>
The bytes can be extracted from a 32 bit integer as follows:
<LISTING>
        red   = (color>> 8)&255;
        green = (color>>16)&255;
        blue  = (color>>24)&255;
</LISTING>
Device drivers may choose to rescale these values to whatever scale
is appropriate.
<P>
Since the lowest byte of color values is not used by the        
color representation it can be used for other purposes.
Currently a non-zero byte is taken to indicate     
an index into a (user defined) table of colors.
Such indices are restricted to the range 1-255.