imager (version 0.42.19)

as.igraph.pixset: Form an adjacency graph from a pixset

Description

Return a graph where nodes are pixels, and two nodes are connected if and only if both nodes are in the pixset, and the pixels are adjacent. Optionnally, add weights corresponding to distance (either 1 or sqrt(2), depending on the orientation of the edge). The graph is represented as an igraph "graph" object

Usage

# S3 method for pixset
as.igraph(x, weighted = TRUE, ...)

Value

an igraph "graph" object

Arguments

x

a pixset

weighted

add weight for distance (default TRUE)

...

ignored

See Also

as.igraph.cimg

Examples

library(igraph)
#Simple 3x3 lattice
px <- px.all(imfill(3,3))
as.igraph(px) %>% plot
#Disconnect central pixel
px[5] <- FALSE
as.igraph(px) %>% plot
#Form graph from thresholded image
im <- load.example("coins")
px <- threshold(im) %>% fill(5)
G <- as.igraph(px)
#Label connected components
v <- (igraph::clusters(G)$membership)
as.cimg(v,dim=dim(px)) %>% plot
#Find a path across the image that avoids all
#the coins
G <- as.igraph(!px)
start <- index.coord(im,data.frame(x=1,y=100))
end <- index.coord(im,data.frame(x=384,y=300))
sp <- igraph::shortest_paths(G,start,end,output="vpath")
path <- sp$vpath[[1]] %>% as.integer %>% coord.index(im,.)