# Replace.im

##### Reset Values in Subset of Image

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.

##### 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):

`i`

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

are indices for the matrix`as.matrix(x)`

; or`i`

can be converted to a point pattern by`as.ppp(i, W=as.owin(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=as.owin(x))`

.
Again the values of the pixel image at the points of
this pattern are changed.

##### 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.

##### See Also

##### 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)
```

*Documentation reproduced from package spatstat, version 1.31-3, License: GPL (>= 2)*