interp.im

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Interpolate a Pixel Image

Interpolates the values of a pixel image at any desired location in the frame.

Keywords
manip, spatial
Usage
interp.im(Z, x, y)
Arguments
Z
Pixel image (object of class "im") with numeric or integer values.
x,y
Vectors of Cartesian coordinates.
Details

A value at each location (x[i],y[i]) will be interpolated using the pixel values of Z at the four surrounding pixel centres, by simple bilinear interpolation.

At the boundary (where (x[i],y[i]) is not surrounded by four pixel centres) the value at the nearest pixel is taken.

Value

  • Vector of interpolated values, with NA for points that lie outside the domain of the image.

Aliases
  • interp.im
Examples
opa <- par(mfrow=c(1,2))
   # coarse image
   V <- as.im(function(x,y) { x^2 + y }, owin(), dimyx=10)
   plot(V, main="coarse image", col=terrain.colors(256))

   # lookup value at location (0.5,0.5)
   V[list(x=0.5,y=0.5)]
   # interpolated value at location (0.5,0.5)
   interp.im(V, 0.5, 0.5)
   # true value is 0.75

   # how to obtain an interpolated image at a desired resolution
   U <- as.im(interp.im, W=owin(), Z=V, dimyx=256)
   plot(U, main="interpolated image", col=terrain.colors(256))
   par(opa)
Documentation reproduced from package spatstat, version 1.31-2, License: GPL (>= 2)

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