# 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=NULL, bilinear=FALSE)
##### Arguments
Z

Pixel image (object of class "im") with numeric or integer values.

x,y

Vectors of Cartesian coordinates. Alternatively x can be a point pattern and y can be missing.

bilinear

Logical value specifying the choice of interpolation rule. If bilinear=TRUE then a bilinear interpolation rule is used. If bilinear=FALSE (the default) then a slightly biased rule is used; this rule is consistent with earlier versions of spatstat.

##### 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.

The arguments x,y can be anything acceptable to xy.coords.

##### Value

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

• interp.im
##### Examples
# NOT RUN {
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)
interp.im(V, 0.5, 0.5, bilinear=TRUE)
# 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 1.61-0, License: GPL (>= 2)

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