A class "im" to represent a two-dimensional pixel image.
The internal representation of images is likely to change in future
releases of spatstat. Do not address the entries in an
image directly. To extract all pixel values from an image object,
use as.matrix.im.
An object of this class represents a two-dimensional pixel image. It specifies
the dimensions of the rectangular array of pixels
\(x\) and \(y\) coordinates for the pixels
a numeric value (``grey value'') at each pixel
If X is an object of type im,
it contains the following elements:
v |
matrix of values |
dim |
dimensions of matrix v |
xrange |
range of \(x\) coordinates of image window |
yrange |
range of \(y\) coordinates of image window |
xstep |
width of one pixel |
ystep |
height of one pixel |
xcol |
vector of \(x\) coordinates of centres of pixels |
Users are strongly advised not to manipulate these entries directly.
Objects of class "im"
may be created by the functions
im and as.im.
Image objects are also returned by various functions including
distmap, Kmeasure, setcov,
eval.im and cut.im.
Image objects may be displayed using the methods
plot.im, image.im, persp.im
and contour.im. There are also methods
print.im for printing information about an image,
summary.im for summarising an image,
mean.im for calculating the average pixel value,
hist.im for plotting a histogram of pixel values,
quantile.im for calculating quantiles of pixel values,
and cut.im for dividing the range of pixel values into
categories.
Pixel values in an image may be extracted
using the subset operator [.im.
To extract all pixel values from an image object,
use as.matrix.im.
The levels of a factor-valued image can be extracted and
changed with levels and levels<-.
Calculations involving one or more images (for example,
squaring all the pixel values in an image, converting numbers to
factor levels, or
subtracting one image from another) can often be done
easily using eval.im.
To find all pixels satisfying
a certain constraint, use solutionset.
Note carefully that the entry v[i,j]
gives the pixel value at the location (xcol[j],yrow[i].
That is, the row index of the matrix v 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 v
and xcol has one entry for each column of v.
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(v)), if you wanted to do it by hand.