compare_colour {farver}

Calculate the distance between colours

Description

There are many ways to measure the distance between colours. farver provides 5 different algorithms, ranging from simple euclidean distance in RGB space, to different perceptual measures such as CIE2000.

Usage

compare_colour(
  from,
  to = NULL,
  from_space,
  to_space = from_space,
  method = "euclidean",
  white_from = "D65",
  white_to = white_from,
  lightness = 2,
  chroma = 1
)

Arguments

from, to

Numeric matrices with colours to compare - the format is the same as that for convert_colour(). If to is not set from will be compared with itself and only the upper triangle will get calculated

from_space, to_space

The colour space of from and to respectively. to_space defaults to be the same as from_space.

method

The method to use for comparison. Either 'euclidean', 'cie1976', 'cie94', 'cie2000', or 'cmc'

white_from, white_to

The white reference of the from and to colour space. Will only have an effect for relative colour spaces such as Lab and luv. Any value accepted by as_white_ref() allowed.

lightness, chroma

Weight of lightness vs chroma when using CMC. Common values are 2 and 1 (default) for acceptability and 1 and 1 for imperceptibility

Value

A numeric matrix with the same number of rows as colours in from and the same number of columns as colours in to. If to is not given, only the upper triangle will be returned.

Handling of non-finite and out of bounds values

NA, NaN, -Inf, and Inf are treated as invalid input and will result in NA values for the colour. If a given colourspace has finite bounds in some of their channels, the input will be capped before conversion, and the output will be capped before returning, so that both input and output colours are valid colours in their respective space. This means that converting back and forth between two colourspaces may result in a change in the colour if the gamut of one of the spaces is less than the other.

Examples

r <- decode_colour(rainbow(10))
h <- decode_colour(heat.colors(15))

# Compare two sets of colours
compare_colour(r, h, 'rgb', method = 'cie2000')

# Compare a set of colours with itself
compare_colour(r, from_space = 'rgb', method = 'cmc')

# Compare colours from different colour spaces
h_luv <- convert_colour(h, 'rgb', 'luv')
compare_colour(r, h_luv, 'rgb', 'luv')