spatstat (version 1.20-2)

as.im: Convert to Pixel Image

Description

Converts various kinds of data to a pixel image

Usage

as.im(X, ...)
  ## S3 method for class 'im':
as.im(X, W=NULL, \dots,
        eps=NULL, dimyx=NULL, xy=NULL,
        na.replace=NULL)
  ## S3 method for class 'owin':
as.im(X, W=NULL, \dots,
        eps=NULL, dimyx=NULL, xy=NULL,
        na.replace=NULL, value=1)
  ## S3 method for class 'tess':
as.im(X, W=NULL, \dots, 
        eps=NULL, dimyx=NULL, xy=NULL,
        na.replace=NULL)
  ## S3 method for class 'function':
as.im(X, W=NULL, \dots,
        eps=NULL, dimyx=NULL, xy=NULL,
        na.replace=NULL)
  ## S3 method for class 'default':
as.im(X, W=NULL, \dots,
        eps=NULL, dimyx=NULL, xy=NULL,
        na.replace=NULL)

Arguments

X

Data to be converted to a pixel image.

W

Window object which determines the spatial domain and pixel array geometry.

...

Additional arguments passed to X when X is a function.

eps,dimyx,xy

Optional parameters passed to as.mask which determine the pixel array geometry. See as.mask.

na.replace

Optional value to replace NA entries in the output image.

value

Optional. The value to be assigned to pixels inside the window, if X is a window.

Value

• An image object of class "im".

Details

This function converts the data X into a pixel image object of class "im" (see im.object). The function as.im is generic, with methods for the classes listed above.

Currently X may be any of the following:

• a pixel image object, of class"im".
• a window object, of class"owin"(seeowin.object). The result is an image with all pixel entries equal tovalueinside the windowX, andNAoutside.
• a tessellation (object of class"tess"). The result is a factor-valued image, with one factor level corresponding to each tile of the tessellation. Pixels are classified according to the tile of the tessellation into which they fall.
• a single number (or a single logical, complex, factor or character value). The result is an image with all pixel entries equal to this constant value inside the windowW(andNAoutside, unless the argumentna.replaceis given). ArgumentWis required.
• a function of the formfunction(x, y, ...)which is to be evaluated to yield the image pixel values. In this case, the additional argumentWmust be present. This window will be converted to a binary image mask. Then the functionXwill be evaluated in the formX(x, y, ...)wherexandyarevectorscontaining the$x$and$y$coordinates of all the pixels in the image mask, and...are any extra arguments given. This function must return a vector or factor of the same length as the input vectors, giving the pixel values.
• a list with entriesx, y, zin the format expected by the standardRfunctionsimage.defaultandcontour.default. That is,zis a matrix of pixel values,xandyare vectors of$x$and$y$coordinates respectively, andz[i,j]is the pixel value for the location(x[i],y[j]).
• a point pattern (object of class"ppp"). See the separate documentation foras.im.ppp.

The spatial domain (enclosing rectangle) of the pixel image is determined by the argument W. If W is absent, the spatial domain is determined by X. When X is a function or a single numerical value, W is required. The pixel array dimensions of the final resulting image are determined by (in priority order)

• the argumenteps,dimyxorxyif present;
• the pixel dimensions of the windowW, if it is present and if it is a binary mask;
• the pixel dimensions ofXif it is an image, a binary mask, or alist(x,y,z);
• the default pixel dimensions, controlled byspatstat.options.

Note that if eps, dimyx or xy is given, this will override the pixel dimensions of X if it has them. Thus, as.im can be used to change an image's pixel dimensions.

If the argument na.replace is given, then all NA entries in the image will be replaced by this value. The resulting image is then defined everwhere on the full rectangular domain, instead of a smaller window. Here na.replace should be a single value, of the same type as the other entries in the image.

See Also

Separate documentation for as.im.ppp

Examples

data(demopat)
  # window object
  W <- demopat$window
  plot(W)
  Z <- as.im(W)
  image(Z)
  # function
  Z <- as.im(function(x,y) {x^2 + y^2}, unit.square())
  image(Z)
  # function with extra arguments
  f <- function(x, y, x0, y0) {
      sqrt((x - x0)^2 + (y-y0)^2)
  }
  Z <- as.im(f, unit.square(), x0=0.5, y0=0.5)
  image(Z)
  # Revisit the Sixties
  data(letterR)
  Z <- as.im(f, letterR, x0=2.5, y0=2)
  image(Z)
  # usual convention in S
  stuff <- list(x=1:10, y=1:10, z=matrix(1:100, nrow=10))
  Z <- as.im(stuff)
  # convert to finer grid
  Z <- as.im(Z, dimyx=256)

  # pixellate the Dirichlet tessellation
  Di <- dirichlet(runifpoint(10))
  plot(as.im(Di))
  plot(Di, add=TRUE)