spatstat (version 1.31-3)

Replace.im: Reset Values in Subset of Image

Description

Reset the values in a subset of a pixel image.

Usage

## S3 method for class 'im':
[(x, i, j) <- value

Arguments

x

A two-dimensional pixel image. An object of class "im".

i

Object defining the subregion or subset to be replaced. Either a spatial window (an object of class "owin"), or a pixel image with logical values, or a point pattern (an object of class "ppp"), or any type of index th

j

An integer or logical vector serving as the column index if matrix indexing is being used. Ignored if i is appropriate to some sort of replacement other than matrix indexing.

value

Vector, matrix, factor or pixel image containing the replacement values. Short vectors will be recycled.

Value

• The image x with the values replaced.

Warning

If you have a 2-column matrix containing the $x,y$ coordinates of point locations, then to prevent this being interpreted as an array index, you should convert it to a data.frame or to a point pattern.

Details

This function changes some of the pixel values in a pixel image. The image x must be an object of class "im" representing a pixel image defined inside a rectangle in two-dimensional space (see im.object).

The subset to be changed is determined by the arguments i,j according to the following rules (which are checked in this order):

1. iis a spatial object such as a window, a pixel image with logical values, or a point pattern; or
2. i,jare indices for the matrixas.matrix(x); or
3. ican be converted to a point pattern byas.ppp(i, W=as.owin(x)), andiis not a matrix.

If i is a spatial window (an object of class "owin"), the values of the image inside this window are changed.

If i is a point pattern (an object of class "ppp"), then the values of the pixel image at the points of this pattern are changed.

If i does not satisfy any of the conditions above, then the algorithm tries to interpret i,j as indices for the matrix as.matrix(x). Either i or j may be missing or blank.

If none of the conditions above are met, and if i is not a matrix, then i is converted into a point pattern by as.ppp(i, W=as.owin(x)). Again the values of the pixel image at the points of this pattern are changed.

See Also

im.object, [.im, [, ppp.object, as.ppp, owin.object

Examples

# make up an image
 X <- setcov(unit.square())
 plot(X)

 # a rectangular subset
 W <- owin(c(0,0.5),c(0.2,0.8))
 X[W] <- 2
 plot(X)

 # a polygonal subset
 data(letterR)
 R <- affine(letterR, diag(c(1,1)/2), c(-2,-0.7))
 X[R] <- 3
 plot(X)

 # a point pattern
 P <- rpoispp(20)
 X[P] <- 10
 plot(X)

 # change pixel value at a specific location
 X[list(x=0.1,y=0.2)] <- 7

 # matrix indexing --- single vector index
 X[1:2570] <- 10
 plot(X)

 # matrix indexing using double indices
 X[1:257,1:10] <- 5
 plot(X)

 # matrix indexing using a matrix of indices
 X[cbind(1:257,1:257)] <- 10
 X[cbind(257:1,1:257)] <- 10
 plot(X)