R: Render Convolution FFT

render_convolution_fft {rayimage}

R Documentation

Render Convolution FFT

Description

Takes an image and applys a convolution operation to it, using a user-supplied or built-in kernel. This function uses a fast-fourier transform and does the convolution in the frequency domain, so it should be faster for much larger kernels.

Usage

render_convolution_fft(
  image,
  kernel = "gaussian",
  kernel_dim = c(11, 11),
  kernel_extent = 3,
  absolute = TRUE,
  pad = 50,
  filename = NULL,
  preview = FALSE,
  gamma_correction = FALSE
)

Arguments

`image`	Image filename or 3-layer RGB array.
`kernel`	Default `gaussian`. By default, an 11x11 Gaussian kernel with a mean of `0` and a standard deviation of `1`, running from `-kernel_extent` to `kernel_extent`. If numeric, this will be the standard deviation of the normal distribution. If a matrix, it will be used directly as the convolution kernel (but resized always to be an odd number of columns and rows).
`kernel_dim`	Default `c(11, 11)`. The dimension of the `gaussian` kernel. Ignored if user specifies their own kernel.
`kernel_extent`	Default `3`. Extent over which to calculate the kernel.
`absolute`	Default `TRUE`. Whether to take the absolute value of the convolution.
`pad`	Default `50`. Amount to pad the image to remove edge effects.
`filename`	Default `NULL`. The filename of the image to be saved. If this is not given, the image will be plotted instead.
`preview`	Default `FALSE`. Whether to plot the convolved image, or just to return the values.
`gamma_correction`	Default `FALSE`. Controls gamma correction when adding colors. Default exponent of 2.2.

Value

3-layer RGB array of the processed image.

Examples

#Perform a convolution with the default gaussian kernel

plot_image(dragon)

#Perform a convolution with the default gaussian kernel
render_convolution_fft(dragon, kernel=0.1,preview = TRUE)

#Increase the width of the kernel

render_convolution_fft(dragon, kernel = 2, kernel_dim=21,kernel_extent=6, preview = TRUE)


#Use a built-in kernel:

render_convolution_fft(dragon, kernel = generate_2d_exponential(falloff=2, dim=31, width=21),
                  preview = TRUE)

#Perform edge detection

edge = matrix(c(-1,-1,-1,-1,8,-1,-1,-1,-1),3,3)
render_convolution_fft(dragon, kernel = edge, preview = TRUE)


#Perform edge detection with Sobel matrices

sobel1 = matrix(c(1,2,1,0,0,0,-1,-2,-1),3,3)
sobel2 = matrix(c(1,2,1,0,0,0,-1,-2,-1),3,3,byrow=TRUE)
sob1 = render_convolution_fft(dragon, kernel = sobel1)
sob2 = render_convolution_fft(dragon, kernel = sobel2)
sob_all = sob1 + sob2
plot_image(sob_all)


#We can also apply this function to matrices:

volcano %>% image()
volcano %>%
 render_convolution_fft(kernel=generate_2d_gaussian(sd=1,dim=31)) %>%
 image()

#Because this function uses the fast-fourier transform, large kernels will be much faster.

render_convolution_fft(dragon, kernel = , preview = TRUE)


#Use a custom kernel (in this case, an X shape):
custom = diag(10) + (diag(10)[,10:1])
#Normalize
custom = custom / 20

plot_image(custom*20)
render_convolution_fft(dragon, kernel = custom, preview = TRUE)

[Package rayimage version 0.5.1 Index]