Description Usage Arguments Details Value Author(s)
Create colors with a given transparency value, or mimick transparency by mixing with the background colour.
1 |
col |
a valid color specification |
alpha |
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 alphacol
is to
mix the input colour A with the background colour found
by par("bg")
. A colour with alpha < 1
thus
actually also prints opaque. If you want to change this
behaviour, let .plottopt$alphamixing = TRUE
.
a colour in RGB format. If alpha < 1, the colour is lighter than the input colour, see the details.
Ute Hahn, ute@imf.au.dk
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