Calculates the distance between non-transparent pixels in images

Compares two versions of the same image (probably original and recolored) by calculating the color distance between the colors of each pair of pixels.

Usage

imDist(
  im1,
  im2,
  color_space = c("Lab", "sRGB", "XYZ", "Luv"),
  ref_white = "D65",
  metric = "euclidean",
  plotting = TRUE,
  palette = "default",
  main = "",
  ...
)

Arguments

im1, im2: Images to compare; must have the same dimensions. Distances will be calculated between each pair of non-transparent pixels.
color_space: Color space in which to calculate distances. One of "sRGB", "Lab", "Luv", or "XYZ". Passed to grDevices::convertColor().
ref_white: Passed to grDevices::convertColor() if color_space = "Lab. Reference white for CIE Lab space.
metric: Distance metric to be used for calculating pairwise pixel distances in the given color space; passed to stats::dist().
plotting: Logical. Plot heatmap of color distances?
palette: If plotting, the color palette to be used. Default is blue to red (colorRamps::blue2red(100)).
main: Plot title.
...: Parameters passed to graphics::image().

Value

A matrix of the same dimensions as the original images, with the distance between non-transparent pixels at each pixel coordinate. Transparent pixels are returned as NA.

Examples

fulgidissima <- system.file("extdata/fulgidissima.png",
                             package = "recolorize")
fulgidissima <- png::readPNG(fulgidissima)
# make an initial histogram fit
# this doesn't look great:
fulgidissima_2bin <- recolorize(fulgidissima, "hist", bins = 2)
#> 
#> Using 2^3 = 8 total bins


# we can compare with the original image by creating the recolored
# image from the colormap
recolored_2bin <- constructImage(fulgidissima_2bin$pixel_assignments,
                                fulgidissima_2bin$centers)
dist_2bin <- imDist(im1 = fulgidissima,
                    im2 = recolored_2bin)


# using 3 bins/channel looks much better:
fulgidissima_3bin <- recolorize(fulgidissima, "hist", bins = 3)
#> 
#> Using 3^3 = 27 total bins


# and we can see that on the heatmap:
recolored_3bin <- constructImage(fulgidissima_3bin$pixel_assignments,
                                fulgidissima_3bin$centers)
dist_3bin <- imDist(im1 = fulgidissima,
                    im2 = recolored_3bin)


# default behavior is to set the color range to the range of distances
# in a single matrix; to compare two different fits, we have to provide
# the same `zlim` scale for both
r <- range(c(dist_2bin, dist_3bin), na.rm = TRUE)

# to reset graphical parameters:
current_par <- graphics::par(no.readonly = TRUE)

# now we can plot them to compare the fits:
layout(matrix(1:2, nrow = 1))
imHeatmap(dist_2bin, range = r)
imHeatmap(dist_3bin, range = r)


# we can also use other color spaces:
rgb_3bin <- imDist(fulgidissima,
                   recolored_3bin,
                   color_space = "sRGB")

# looks oddly worse, but to keep things in perspective,
# you can set the range to the maximum color distance in RGB space:
imHeatmap(rgb_3bin, range = c(0, sqrt(3)))

# not useful for troubleshooting, but broadly reassuring!

# reset:
graphics::par(current_par)