Replace.im {spatstat.geom}

Reset Values in Subset of Image

Description

Reset the values in a subset of a pixel image.

Usage

  ## S3 replacement method for class 'im'
x[i, j, ..., drop=TRUE] <- 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 that applies to a matrix, or something that can be converted to a point pattern by as.ppp (using the window of x).

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.

...

Ignored.

drop

Logical value specifying what happens when i and j are both missing. See Details.

value

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

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. i is a spatial object such as a window, a pixel image with logical values, or a point pattern; or

2. i,j are indices for the matrix as.matrix(x); or

3. i can be converted to a point pattern by as.ppp(i, W=Window(x)), and i is 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=Window(x)). Again the values of the pixel image at the points of this pattern are changed.

If i and j are both missing, as in the call x[] <- value, then all pixel values in x are replaced by value:

• If drop=TRUE (the default), then this replacement applies only to pixels whose values are currently defined (i.e. where the current pixel value is not NA). If value is a vector, then its length must equal the number of pixels whose values are currently defined.

• If drop=FALSE then the replacement applies to all pixels inside the rectangle Frame(x). If value is a vector, then its length must equal the number of pixels in the entire rectangle.

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.

Author(s)

Adrian Baddeley [e-mail], Rolf Turner [e-mail] and Ege Rubak [e-mail].

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
 R <- affine(letterR, diag(c(1,1)/2), c(-2,-0.7))
 X[R] <- 3
 plot(X)

 # a point pattern
 X[cells] <- 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)

 # Blank indices
 Y <- as.im(letterR)
 plot(Y)
 Y[] <- 42  # replace values only inside the window 'R'
 plot(Y)
 Y[drop=FALSE] <- 7 # replace all values in the rectangle
 plot(Y)

 Z <- as.im(letterR)
 Z[] <- raster.x(Z, drop=TRUE) # excludes NA
 plot(Z)
 Z[drop=FALSE] <- raster.y(Z, drop=FALSE) # includes NA
 plot(Z)