spatial: Spatial linear transformations

In aoles/EBImage: Image processing and analysis toolbox for R

Spatial linear transformations

Description

The following functions perform all spatial linear transforms: reflection, rotation, translation, resizing, and general affine transform.

Usage

flip(x)
flop(x)
rotate(x, angle, filter = "bilinear", output.dim, output.origin, ...)
translate(x, v, filter = "none", ...)
resize(x, w, h, output.dim = c(w, h), output.origin = c(0, 0), antialias = FALSE, ...)

affine(x, m, filter = c("bilinear", "none"), output.dim, bg.col = "black", antialias = TRUE)

Arguments

x	An Image object or an array.
angle	A numeric specifying the image rotation angle in degrees.
v	A vector of 2 numbers denoting the translation vector in pixels.
w, h	Width and height of the resized image. One of these arguments can be missing to enable proportional resizing.
filter	A character string indicating the interpolating sampling filter. Valid values are 'none' or 'bilinear'. See Details.
output.dim	A vector of 2 numbers indicating the dimension of the output image. For affine and translate the default is dim(x), for resize it equals c(w, h), and for rotate it defaults to the bounding box size of the rotated image.
output.origin	A vector of 2 numbers indicating the output coordinates of the origin in pixels.
m	A 3x2 matrix describing the affine transformation. See Details.
bg.col	Color used to fill the background pixels, defaults to "black". In the case of multi-frame images the value is recycled, and individual background for each frame can be specified by providing a vector.
antialias	If TRUE, perform bilinear sampling at image edges using bg.col.
...	Arguments to be passed to affine, such as filter, output.dim, bg.col or antialias.

Details

flip mirrors x around the image horizontal axis (vertical reflection).

flop mirrors x around the image vertical axis (horizontal reflection).

rotate rotates the image clockwise by the given angle around the origin specified in output.origin. If no output.origin is provided, the result will be centered in a recalculated bounding box unless output.dim is provided.

resize scales the image x to the desired dimensions. The transformation origin can be specified in output.origin. For example, zooming about the output.origin can be achieved by setting output.dim to a value different from c(w, h).

affine returns the affine transformation of x, where pixels coordinates, denoted by the matrix px, are transformed to cbind(px, 1)%*%m.

All spatial transformations except flip and flop are based on the general affine transformation. Spatial interpolation can be either none, also called nearest neighbor, where the resulting pixel value equals to the closest pixel value, or bilinear, where the new pixel value is computed by bilinear approximation of the 4 neighboring pixels. The bilinear filter gives smoother results.

Value

An Image object or an array, containing the transformed version of x.

Author(s)

Gregoire Pau, 2012

See Also

transpose

Examples

  x <- readImage(system.file("images", "sample.png", package="EBImage"))
  display(x)

  display( flip(x) )
  display( flop(x) ) 
  display( resize(x, 128) )
  display( rotate(x, 30) )
  display( translate(x, c(120, -20)) )

  m <- matrix(c(0.6, 0.2, 0, -0.2, 0.3, 300), nrow=3)
  display( affine(x, m) )

aoles/EBImage documentation built on Oct. 16, 2024, 2:06 p.m.