imager (version 0.42.19)

grow: Grow/shrink a pixel set

Description

Grow/shrink a pixel set through morphological dilation/erosion. The default is to use square or rectangular structuring elements, but an arbitrary structuring element can be given as input. A structuring element is a pattern to be moved over the image: for example a 3x3 square. In "shrink" mode, a element of the pixset is retained only if and only the structuring element fits entirely within the pixset. In "grow" mode, the structuring element acts like a neighbourhood: all pixels that are in the original pixset *or* in the neighbourhood defined by the structuring element belong the new pixset.

Usage

grow(px, x, y = x, z = x, boundary = TRUE)
shrink(px, x, y = x, z = x, boundary = TRUE)

Arguments

px

a pixset

x

either an integer value, or an image/pixel set.

y

width of the rectangular structuring element (if x is an integer value)

z

depth of the rectangular structuring element (if x is an integer value)

boundary

are pixels beyond the boundary considered to have value TRUE or FALSE (default TRUE)

Functions

• shrink(): shrink pixset using erosion

Examples

#A pixel set:
a <- grayscale(boats) > .8
plot(a)
#Grow by a 8x8 square
grow(a,8) %>% plot
#Grow by a 8x2 rectangle
grow(a,8,2) %>% plot
#Custom structuring element
el <- matrix(1,2,2) %>% as.cimg
all.equal(grow(a,el),grow(a,2))
#Circular structuring element
px.circle(5) %>% grow(a,.) %>% plot
#Sometimes boundary conditions matter
im <- imfill(10,10)
px <- px.all(im)
shrink(px,3,bound=TRUE) %>% plot(main="Boundary conditions: TRUE")
shrink(px,3,bound=FALSE) %>% plot(main="Boundary conditions: FALSE")