Replace.im
Reset Values in Subset of Image
Reset the values in a subset of a pixel image.
Usage
# S3 method for 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 byas.ppp
(using the window ofx
).- 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
andj
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):
i
is a spatial object such as a window, a pixel image with logical values, or a point pattern; ori,j
are indices for the matrixas.matrix(x)
; ori
can be converted to a point pattern byas.ppp(i, W=Window(x))
, andi
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 notNA
). Ifvalue
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 rectangleFrame(x)
. Ifvalue
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.
See Also
Examples
# NOT RUN {
# 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)
# 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)
# }