Create a colour map (colour lookup table).
colourmap(col, ..., range=NULL, breaks=NULL, inputs=NULL, gamma=1)A function, which is also an object of class "colourmap".
Vector of values specifying colours
Ignored.
Interval to be mapped.
A numeric vector of length 2, specifying the endpoints of the
range of values to be mapped.
Incompatible with breaks or inputs.
Values to which the colours are associated.
A factor or vector of the same length as col.
Incompatible with breaks or range.
Breakpoints for the colour map.
A numeric vector of length equal to length(col)+1.
Incompatible with range or inputs.
Exponent for the gamma correction, when range is given.
A single positive number.
See Details.
Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner rolfturner@posteo.net and Ege Rubak rubak@math.aau.dk.
A colour map is a mechanism for associating colours with data. It can be regarded as a function, mapping data to colours.
The command colourmap creates an object representing
a colour map, which can then be used to control the plot commands
in the spatstat package. It can also be used to compute the
colour assigned to any data value.
The argument col specifies the colours to which
data values will be mapped. It should be a vector
whose entries can be interpreted as colours by the standard
R graphics system. The entries can be string names of colours
like "red", or integers that refer to
colours in the standard palette, or strings containing
six-letter hexadecimal codes like "#F0A0FF".
Exactly one of the arguments range, inputs or breaks
must be specified by name.
If inputs is given, then it should be a vector or factor,
of the same length as col. The entries of inputs can be
any atomic type (e.g. numeric, logical, character, complex) or factor
values. The resulting colour map associates the value inputs[i]
with the colour col[i].
The argument col should have the same length as inputs.
If range is given, then it determines the interval of the real
number line that will be mapped. It should be a numeric vector of
length 2. The interval will be divided evenly into bands, each of which is
assigned one of the colours in col. (If gamma is given,
then the bands are equally spaced on a scale where the original values
are raised to the power gamma.)
If breaks is given, then it determines the precise intervals
of the real number line
which are mapped to each colour. It should be a numeric vector,
of length at least 2, with entries that are in increasing order.
Infinite values are allowed. Any number in the range
between breaks[i] and breaks[i+1] will be mapped to the
colour col[i].
The argument col should have length equal to
length(breaks) - 1.
It is also permissible for col to be a single colour value,
representing a trivial colour map in which all data values are mapped to
the same colour.
The result is an object of class "colourmap".
There are print and plot methods for this class.
Some plot commands in the spatstat package accept an object
of this class as a specification of the colour map.
The result is also a function f which can be used to compute
the colour assigned to any data value.
That is, f(x) returns the character value of the colour assigned
to x. This also works for vectors of data values.
The plot method plot.colourmap.
See the R help file on
colours for information about the colours
that R recognises, and how to manipulate them.
To make a smooth transition between colours, see
interp.colourmap.
To alter individual colour values, see
tweak.colourmap.
To extract or replace all colour values, see
colouroutputs.
See also restrict.colourmap.
See colourtools
for more tools to manipulate colour values.
See lut for lookup tables.
# colour map for real numbers, using breakpoints
cr <- colourmap(c("red", "blue", "green"), breaks=c(0,5,10,15))
cr
cr(3.2)
cr(c(3,5,7))
# a large colour map
co <- colourmap(rainbow(100), range=c(-1,1))
co(0.2)
# colour map for discrete set of values
ct <- colourmap(c("red", "green"), inputs=c(FALSE, TRUE))
ct(TRUE)
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