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Fast colour interpolation

Source: R/colour-ramp.R
colour_ramp.Rd

Returns a function that maps the interval [0,1] to a set of colours. Interpolation is performed in the CIELAB colour space. Similar to colorRamp(space = 'Lab'), but hundreds of times faster, and provides results in "#RRGGBB" (or "#RRGGBBAA") character form instead of RGB colour matrices.

Usage

colour_ramp(colors, na.color = NA, alpha = TRUE)

Arguments

colors

Colours to interpolate; must be a valid argument to grDevices::col2rgb(). This can be a character vector of "#RRGGBB" or "#RRGGBBAA", colour names from grDevices::colors(), or a positive integer that indexes into grDevices::palette().

na.color

The colour to map to NA values (for example, "#606060" for dark grey, or "#00000000" for transparent) and values outside of [0,1]. Can itself by NA, which will simply cause an NA to be inserted into the output.

alpha

Whether to include alpha transparency channels in interpolation. If TRUE then the alpha information is included in the interpolation. The returned colours will be provided in "#RRGGBBAA" format when needed, i.e., in cases where the colour is not fully opaque, so that the "AA" part is not equal to "FF". Fully opaque colours will be returned in "#RRGGBB" format. If FALSE, the alpha information is discarded before interpolation and colours are always returned as "#RRGGBB".

Value

A function that takes a numeric vector and returns a character vector of the same length with RGB or RGBA hex colours.

See also

colorRamp

Examples

ramp <- colour_ramp(c("red", "green", "blue"))
show_col(ramp(seq(0, 1, length = 12)))