im
Create a Pixel Image Object
Creates an object of
class "im"
representing a two-dimensional pixel image.
Usage
im(mat, xcol=seq_len(ncol(mat)), yrow=seq_len(nrow(mat)),
xrange=NULL, yrange=NULL,
unitname=NULL)
Arguments
- mat
- matrix or vector containing the pixel values of the image.
- xcol
- vector of $x$ coordinates for the pixel grid
- yrow
- vector of $y$ coordinates for the pixel grid
- xrange,yrange
- Optional. Vectors of length 2 giving the $x$ and $y$
limits of the enclosing rectangle.
(Ignored if
xcol
,yrow
are present.) - unitname
- Optional. Name of unit of length. Either a single character string, or a vector of two character strings giving the singular and plural forms, respectively.
Details
This function creates an object of class "im"
representing
a two-dimensional pixel image. See im.object
for details of this class.
The matrix mat
contains the mat[i,j]
gives the pixel value at the location (xcol[j],yrow[i])
.
That is, the row index of the matrix mat
corresponds
to increasing y coordinate, while the column index of mat
corresponds to increasing x coordinate.
Thus yrow
has one entry for each row of mat
and xcol
has one entry for each column of mat
.
Under the usual convention in R, a correct
display of the image would be obtained by transposing the matrix, e.g.
image.default(xcol, yrow, t(mat))
, if you wanted to do it by hand.
The entries of mat
may be numeric (real or integer), complex,
logical, character, or factor values.
If mat
is not a matrix, it will be converted into
a matrix with nrow(mat) = length(yrow)
and
ncol(mat) = length(xcol)
.
To make a factor-valued image, note that
Rhas a quirky way of handling matrices with
factor-valued entries. The command matrix
cannot be used
directly, because it destroys factor information.
To make a factor-valued image, do one of the following:
- Create a
factor
containing the pixel values, saymat <- factor(.....)
, and then assign matrix dimensions to it bydim(mat) <- c(nr, nc)
wherenr, nc
are the numbers of rows and columns. The resulting objectmat
is both a factor and a vector. - Supply
mat
as a one-dimensional factor and specify the argumentsxcol
andyrow
to determine the dimensions of the image. - Use the functions
cut.im
oreval.im
to make factor-valued images from other images).
im.object
. To convert other kinds of data to a pixel image (for example,
functions or windows), use as.im
.
Warnings
The internal representation of images is likely to change in future
releases of as.matrix.im
or [.im
.
See Also
Examples
vec <- rnorm(1200)
mat <- matrix(vec, nrow=30, ncol=40)
whitenoise <- im(mat)
whitenoise <- im(mat, xrange=c(0,1), yrange=c(0,1))
whitenoise <- im(mat, xcol=seq(0,1,length=40), yrow=seq(0,1,length=30))
whitenoise <- im(vec, xcol=seq(0,1,length=40), yrow=seq(0,1,length=30))
plot(whitenoise)
# Factor-valued images:
f <- factor(letters[1:12])
dim(f) <- c(3,4)
Z <- im(f)
# Factor image from other image:
cutwhite <- cut(whitenoise, 3)
plot(cutwhite)
# Factor image from raw data
cutmat <- cut(mat, 3)
dim(cutmat) <- c(30,40)
cutwhite <- im(cutmat)
plot(cutwhite)