Create surfaces and trajectories

The central idea of this package is to create sequential palettes by projecting a chroma trajectory onto a hue surface. Use these functions to build the surfaces and trajectories.

These functions themselves return functions.

The function pth_new_hue_surface() takes one or two values of hue and two values of lum. It returns a function that returns hue as a linear function of lum.

The function pth_new_chroma_trajectory() takes an equal number of lum and chroma values. These serve as control points for a Bézier curve. It returns a function that given input values 0 <= x <= 1, returns a matrix with as many rows as input values; lum and chroma are the columns.

One thing to keep in mind when designing a trajectory: although it is a good thing to keep the trajectory within the gamut, it is not necessary (or perhaps not even desirable) to keep the control points within the gamut.

pth_new_hue_surface(hue, lum = c(0, 100))

pth_new_chroma_trajectory(chroma, lum)

Arguments

hue

numeric values for hue (degrees), input values are not constrained to 0 <= hue < 360.

lum

numeric values for luminance

chroma

numeric values for chroma.

Value

pth_new_hue_surface()

function with S3 class pth_hue_surface: for each given value of luminance 0 <= lum <= 100, returns a value for hue 0 <= hue < 360.

pth_new_chroma_trajectory()

function with S3 class pth_chroma_trajectory: for each given value 0 <= x <= 1, returns a set of luminance and chroma values as matrix.

Examples

 # create surfaces
 # provide single value of hue for constant
 sfc <- pth_new_hue_surface(270)
 sfc(c(0, 50, 100))
#> [1] 270 270 270

 # provide two values of hue to correspond to luminance values
 sfc <- pth_new_hue_surface(c(220, 270))
 sfc(c(0, 50, 100))
#> [1] 220 245 270

 # provide other values for luminance, if you like
 sfc <- pth_new_hue_surface(c(220, 270), lum = c(25, 75))
 sfc(c(0, 25, 50, 75, 100))
#> [1] 195 220 245 270 295

 # create a trajectory
 traj <-
   pth_new_chroma_trajectory(chroma = c(0, 100, 0), lum = c(20, 50, 80))
 traj(seq(0, 1, by = 0.1))
#>       lum chroma
#>  [1,]  20      0
#>  [2,]  26     18
#>  [3,]  32     32
#>  [4,]  38     42
#>  [5,]  44     48
#>  [6,]  50     50
#>  [7,]  56     48
#>  [8,]  62     42
#>  [9,]  68     32
#> [10,]  74     18
#> [11,]  80      0