| im {spatstat} | R Documentation |
Creates an object of
class "im" representing a two-dimensional pixel image.
im(mat, xcol=seq(ncol(mat)), yrow=seq(nrow(mat)), lev=levels(mat), units=NULL)
mat |
matrix or vector containing the pixel values of the image. |
xcol |
vector of x coordinates for the pixel gid |
yrow |
vector of y coordinates for the pixel grid |
lev |
possible factor levels, if mat should be interpreted
as a factor.
|
units |
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. |
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 ‘greyscale’ values
for a rectangular grid of pixels.
Note carefully that the entry 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).
R{} does not allow a matrix to have
factor-valued entries. So to make a factor-valued image from raw data,
you must supply mat as a factor vector and specify the arguments
xcol and yrow to determine the dimensions of the image.
See the examples. (Alternatively you can use the functions
cut.im or eval.im to make factor-valued
images from other images).
For a description of the methods available for pixel image objects,
see im.object.
To convert other kinds of data to a pixel image (for example,
functions or windows), use as.im.
The internal representation of images is likely to change in future
releases of spatstat. The safe way to extract pixel values
from an image object is to use as.matrix.im
or [.im.
Adrian Baddeley adrian@maths.uwa.edu.au http://www.maths.uwa.edu.au/~adrian/ and Rolf Turner rolf@math.unb.ca http://www.math.unb.ca/~rolf
im.object,
as.im,
as.matrix.im,
[.im,
eval.im
vec <- rnorm(1200) mat <- matrix(vec, nrow=30, ncol=40) whitenoise <- im(mat) 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: cutvec <- cut(mat, 3) # although mat was a matrix, cutvec is a vector, with factor values cutwhite <- im(cutvec, xcol=seq(0,1,length=40), yrow=seq(0,1,length=30)) # cutwhite is a factor-valued image plot(cutwhite)