R: Pixmap Images

pixmap {pixmap} | R Documentation

## 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)

[Package pixmap version 0.4-11 Index]