pixmap: Pixmap Images

In pixmap: Bitmap Images / Pixel Maps

Pixmap Images

Description

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.

Usage

pixmap(data=NULL, nrow=dim(data)[1], ncol=dim(data)[2],
       bbox=NULL, bbcent=FALSE, cellres=NULL)
pixmapRGB(data, ...)
pixmapGrey(data, ...)
pixmapIndexed(data, col, ...)

Arguments

data	An optional data vector.
nrow	Vertical size of the image in pixels.
ncol	Horizontal size of the image in pixels.
bbox	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)

pixmap documentation built on May 29, 2024, 9:47 a.m.