Create colors with a given transparency value, or mimick transparency by mixing with the background colour.
a valid color specification
numeric, alpha level, between 0 and 1.
alphacol follows the concept of alpha compositing:
A number α between 0 and 1 controls how opaque the colour is. When printing a colour A with alpha-level α over a colour B, the result becomes αA + (1-α)B. Thus,
alpha = 1 equals to a colour that overplots other colours, and for
alpha = 0, the colour is invisible.
R allows to define RGB colours with true alpha transparency, however, not
all devices support that. Therefore, the default behaviour of
is to mix the input colour A with the background colour found by
A colour with
alpha < 1 thus actually also prints opaque.
If you want to change this behaviour once, let
alphamix = TRUE.
To change it globally, call
ploptions(alphamix = TRUE)
a colour in RGB format. If alpha < 1, the colour is lighter than the input colour, see the details.
Ute Hahn, email@example.com
ploptions for setting package options.
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