R/wavelength2RGB.R

In ajfedorec/wavelength2colour: Convert a wavelength (in nm) to a usable colour

#' Turn a wavelength (in nm) in to an RGB vector.
#'
#' Code adapted from \url{http://www.efg2.com/Lab/ScienceAndEngineering/Spectra.htm}
#'
#' @param wavelength a numerical wavelength to convert to RGB.
#'
#' @return a vector of three numeric values representing the RGB components.
#' @export
wavelength2RGB <- function(wavelength){
  # CONST
  gamma        <-   0.80
  intensity_max <-   255

  adjust <- function(colour, factor){
    if (colour == 0.0){
      return(0)
    }
    else{
      return(round(intensity_max * (colour * factor) ^ gamma))
    }
  }

  if (wavelength >= 380 && wavelength < 440){
    red   <- - (wavelength - 440) / (440 - 380);
    green <- 0.0;
    blue  <- 1.0
  }
  else if (wavelength >= 440 && wavelength < 490){
    red   <- 0.0;
    green <- (wavelength - 440) / (490 - 440);
    blue  <- 1.0
  }
  else if (wavelength >= 490 && wavelength < 510){
    red   <- 0.0;
    green <- 1.0;
    blue  <- - (wavelength - 510) / (510 - 490)
  }
  else if (wavelength >= 510 && wavelength < 580){
    red   <- (wavelength - 510) / (580 - 510);
    green <- 1.0;
    blue  <- 0.0
  }
  else if (wavelength >= 580 && wavelength < 645){
    red   <- 1.0;
    green <- - (wavelength - 645) / (645 - 580);
    blue  <- 0.0
  }
  else if (wavelength >= 645 && wavelength <= 780){
    red   <- 1.0;
    green <- 0.0;
    blue  <- 0.0
  }
  else{
    red   <- 0.0;
    green <- 0.0;
    blue  <- 0.0
  }
  # Let the intensity fall off near the vision limits
  if (wavelength >= 380 && wavelength < 420){
    factor <- 0.3 + 0.7 * (wavelength - 380) / (420 - 380);
  }
  else if (wavelength >= 420 && wavelength < 700){
    factor <- 1.0;
  }
  else if (wavelength >= 700 && wavelength <= 780){
    factor <- 0.3 + 0.7 * (780 - wavelength) / (780 - 700)
  }
  else{
    factor <- 0.0
  }
  R <- adjust(red,   factor);
  G <- adjust(green, factor);
  B <- adjust(blue,  factor)

  return(c(R, G, B))
}