Thin (skeletonize) a binary image

Reduce a binary image to its one-pixel-wide skeleton using one of the supported thinning algorithms.

Usage

thin(
  image,
  method = c("zhang_suen", "guo_hall", "lee", "k3m"),
  max_iter = 1000L
)

Arguments

image

A binary image: a matrix or array where non-zero values are foreground and zero values are background. Logical, integer, and numeric inputs are all accepted. The image is treated as a 2-D matrix; arrays with more than two dimensions are not yet supported.

method

Algorithm to use. One of "zhang_suen" (default, matches EBImage::thinImage), "guo_hall", "lee" (2-D adaptation of Lee, Kashyap & Chu 1994), or "k3m" (Saeed et al. 2010). See vignette("choosing-a-method") for guidance on which to pick.

max_iter

Maximum number of passes. Default 1000. Real binary images of typical sizes converge well under 50 passes; the limit is a safety bound against pathological inputs.

Value

A matrix of the same shape and storage mode as image, with foreground pixels marking the thinned skeleton and the rest set to background.

Examples

# A 3x3 solid square thins to a single foreground pixel.
m <- matrix(c(0, 0, 0, 0, 0,
              0, 1, 1, 1, 0,
              0, 1, 1, 1, 0,
              0, 1, 1, 1, 0,
              0, 0, 0, 0, 0),
            nrow = 5, byrow = TRUE)
thin(m, method = "zhang_suen")
#>      [,1] [,2] [,3] [,4] [,5]
#> [1,]    0    0    0    0    0
#> [2,]    0    0    0    0    0
#> [3,]    0    0    1    0    0
#> [4,]    0    0    0    0    0
#> [5,]    0    0    0    0    0
thin(m, method = "guo_hall")
#>      [,1] [,2] [,3] [,4] [,5]
#> [1,]    0    0    0    0    0
#> [2,]    0    0    0    0    0
#> [3,]    0    0    1    0    0
#> [4,]    0    0    0    0    0
#> [5,]    0    0    0    0    0