pixmap (version 0.2-1)

pixmap: 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=0, nrow=dim(data)[1], ncol=dim(data)[2],
       col=NULL, type=c("grey", "rgb", "indexed"),
       bbox=NULL, bbcent=FALSE, cellres=NULL)
as.pixmapRGB(object)
as.pixmapGrey(object, coefs=c(0.30, 0.59, 0.11))
as.pixmapIndexed(object)
## S3 method for class 'pixmap':
plot(x, ...)

Arguments

data

An optional data vector.

nrow

Vertical size of the image in pixels.

ncol

Horizontal size of the image in pixels.

col

Character vector of colors to use if type is "indexed", or a function like rainbow which can be used to create a palette.

type

Type of pixmap to create, see details below.

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.

x, object

Object of class "pixmap"

coefs

Coefficients used for converting a color image to grey. The grey value is simply the weighted sum of the channels red, green and blue in each pixel.

...

Graphical parameters passed to image.

Details

Class "pixmap" has currently the three subclasses "pixmapRGB", "pixmapGrey", and "pixmapIndexed". The optional bounding box specifies a coordinate system for the image and is, e.g., used for labelling the axes in plots. Methods for coercion between all formats are available.

RGB pixmaps are three-dimensional arrays where the first two dimensions give the size of the image in pixels and the third dimension is for the three color channels red, green and blue. Elements of the array must be between 0 (=color off) and 1 (=color at maximum), otherwise data is rescaled appropriatly.

Grey and indexed pixmaps are matrices, the element [1,1] corresponds to the upper left corner as usual. For grey pixmaps the elements must be between 0 (black) and 1 (white). Indexed pixmaps have integer elements, each giving the index number corresponding to the palette specified in "col". Again, automatic rescaling is attempted if data is not inside the allowed range. Colors are given using the usual R color strings (either names like "red" or hex values like "#FF0000"). Alternatively, a function to create a color palette can be specified, see rainbow or heat.colors for examples.

If the data argument is 2- or 3-diemnsional, 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 parametrs 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.

See Also

read.pnm

Examples

## A simple example
 x <- pixmap(rep(1:8, 9), nrow=6, col=terrain.colors(8), type="indexed")
 plot(x)
 ## The same with different colors, and passing the function instead of
 ## a color vector 
 x <- pixmap(rep(1:8, 9), nrow=6, col=rainbow, type="indexed")
 plot(x)
 plot(x, asp=.5, axes=TRUE)
 plot(as.pixmapGrey(x))

 ## 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 <- pixmap(c(z1,z2,z3), 100, 100, type="rgb", bbox=c(-1,-1,1,1))
 plot(z, axes=TRUE)