image_canny_edge_detector {image.CannyEdges}

Canny Edge Detector for Images

Description

Canny Edge Detector for Images. See https://en.wikipedia.org/wiki/Canny_edge_detector. Adapted from https://github.com/Neseb/canny.

Usage

image_canny_edge_detector(x, s = 2, low_thr = 3, high_thr = 10, accGrad = TRUE)

Arguments

x

a matrix of image pixel values in the 0-255 range.

s

sigma, the Gaussian filter variance. Defaults to 2.

low_thr

lower threshold value of the algorithm. Defaults to 3.

high_thr

upper threshold value of the algorithm. Defaults to 10

accGrad

logical indicating to trigger higher-order gradient

Value

a list with element edges which is a matrix with values 0 or 255 indicating in the same dimension of x. Next to that the list also contains the input parameters s, low_thr, high_thr and accGrad, the number of rows (nx) and columns of the image (ny) and the number of pixels which have value 255 (pixels_nonzero).

Examples

if(requireNamespace("pixmap")){

library(pixmap)
imagelocation <- system.file("extdata", "chairs.pgm", package="image.CannyEdges")
image <- read.pnm(file = imagelocation, cellres = 1)
x <- image@grey * 255

edges <- image_canny_edge_detector(x)
edges
plot(edges)

}


if(requireNamespace("magick")){
##
## image_canny_edge_detector expects a matrix as input
##  if you have a jpg/png/... convert it to pgm first or take the r/g/b channel
library(magick)
x <- image_read(system.file("extdata", "atomium.jpg", package="image.CannyEdges"))
x
image <- image_data(x, channels = "Gray")
image <- as.integer(image, transpose = TRUE)
edges <- image_canny_edge_detector(image)
edges
plot(edges)
}

if(requireNamespace("pixmap") && requireNamespace("magick")){
##
## image_canny_edge_detector expects a matrix as input
##  if you have a jpg/png/... convert it to pgm first or take the r/g/b channel
library(magick)
library(pixmap)
f <- tempfile(fileext = ".pgm")
x <- image_read(system.file("extdata", "atomium.jpg", package="image.CannyEdges"))
x <- image_convert(x, format = "pgm", depth = 8)
image_write(x, path = f, format = "pgm")

image <- read.pnm(f, cellres = 1)
edges <- image_canny_edge_detector(image@grey * 255)
edges
plot(edges)

file.remove(f)
}