The family "pixmap" (“pixel maps”) of classes provides
methods for creating,
plotting and converting bitmapped images in three different formats:
RGB, grey and indexed pixmaps.
Bounding box of the image, vector of length 4 of form c(x1,
y1, x2, y2) with coordinates for the lower left corner and upper
right corner.
bbcent
Logical, if TRUE the bounding box specifies the
coordinates of the centers of the lower left and upper right pixels,
default is the coordinates of the lower left and upper right corner
of the image.
cellres
Numeric vector of length 1 or 2, specifies the
resolution of pixels in horizontal and vertical direction. If only
one value is given, resolution in both directions is identical.
col
Character vector of colors to use for indexed pictures, or
a function like rainbow which can
be used to create a palette. Colors set to NA are
transparent; this can be used,e.g., for overlaying plots.
...
Additional arguments passed to pixmap().
Details
If the data argument is 2- or 3-dimensional, nrow and
ncol default to the first two dimensions of data, such
that pixmap does the expected when given a matrix or an array.
The arguments bbox, bbcent and cellres can be
used to specify a coordinate system for the image. Note that together
with nrow and ncol the coordinate system is
overspecified, hence not all parameters must be specified, the rest is
computed or set to sensible defaults.
For bbcent=FALSE we have
cellres[1] = (bbox[3]-bbox[1])/ncol
and
cellres[2] = (bbox[4]-bbox[2])/nrow, for bbcent=TRUE
we get
cellres[1] = (bbox[3]-bbox[1])/(ncol-1)
and
cellres[2] = (bbox[4]-bbox[2])/(nrow-1).
The name pixmap was chosen because both image and
bitmap are already used in R.
Author(s)
Friedrich Leisch
See Also
pixmap-class, read.pnm
Examples
## A simple example
x <- pixmapIndexed(rep(1:8, 9), nrow=6, col=terrain.colors(8))
plot(x)
## The same with different colors, and passing the function instead of
## a color vector
x <- pixmapIndexed(rep(1:8, 9), nrow=6, col=rainbow)
plot(x)
plot(x, asp=.5, axes=TRUE)
## Read data from a file
x <- read.pnm(system.file("pictures/logo.ppm", package="pixmap")[1])
plot(x)
## Another example that math can be beautiful
x <- seq(-3,3,length=100)
z1 <- outer(x,x,function(x,y) abs(sin(x)*sin(y)))
z2 <- outer(x,x,function(x,y) abs(sin(2*x)*sin(y)))
z3 <- outer(x,x,function(x,y) abs(sin(x)*sin(2*y)))
## Notice that we specify a bounding box to get the correct
## coordinates on the axes. z1, z2 and z3 are used as red,
## green and blue channel, respectively.
z <- pixmapRGB(c(z1,z2,z3), 100, 100, bbox=c(-1,-1,1,1))
plot(z, axes=TRUE)
## look at a grey version
plot(as(z, "pixmapGrey"))
## subsetting works as expected
plot(z[1:20,])
plot(z[,1:40])
plot(z[1:20,10:40])
## overlay different images using transparency
## base image as before
x <- pixmapIndexed(rep(1:8, 9), nrow=6, col=terrain.colors(8))
plot(x)
## make a mask of vertical bars
mask <- array(0,dim=c(6,12))
mask[,seq(1,12,3)] <- 1
## plot this mask over existing image with transparent and black color
plot(pixmapIndexed(mask,col=c("NA","#000000")),add=TRUE)