Turn an image into the points that draw it

This function loads an image file and returns the position of every pixel that passes a brightness threshold. These are the points that surreal_image() hides. Getting them first lets you look at them, change them, or combine them with other points before handing them to surreal().

Usage

surreal_image_points(
  image_path,
  mode = "auto",
  threshold = NULL,
  max_points = NULL,
  invert_y = TRUE,
  verbose = FALSE
)

Arguments

image_path

Character. Path to an image file or a URL (PNG, JPEG, BMP, TIFF, or SVG).

mode

Character. Either "auto" (default) to automatically detect, "dark" to select dark pixels, or "light" to select light pixels.

threshold

Numeric or NULL. Value between 0 and 1 for grayscale threshold. If NULL (default), automatically calculated using Otsu's method. For "dark" mode, pixels below threshold are selected. For "light" mode, pixels above threshold are selected.

max_points

Integer or NULL. Maximum number of points to use. If NULL (default), automatically estimated based on image size (typically 2000-5000 points). Set to Inf to use all points without downsampling.

invert_y

Logical. If TRUE, flip y-coordinates so image appears right-side up in residual plot. Default is TRUE.

verbose

Logical. If TRUE, prints progress information. Default is FALSE.

Value

A data.frame with one row for each point of the image and two columns, x and y.

Details

The mode, the threshold and the number of points are chosen automatically unless you set them, as described for surreal_image().

See also

surreal_image() to go from an image to a dataset in one step. surreal_text_points() for the points of a text message.

Examples

if (FALSE) { # \dontrun{
# The points of the R logo
points <- surreal_image_points("https://www.r-project.org/logo/Rlogo.png")
plot(points, pch = 16, asp = 1)

# Hide them in a dataset, as surreal_image() does
result <- surreal(points)
} # }