render_alpha_outline: Render Alpha Outline

In rayimage: Image Processing for Simulated Cameras

Render Alpha Outline

Description

Creates a colored RGBA outline or halo from an image alpha channel or a supplied mask. When image is supplied, the original image is composited over the outline by default.

Usage

render_alpha_outline(
  image = NULL,
  mask = NULL,
  expand = 0,
  edge_softness = 0.1,
  blur = 0,
  gap_fill = 1,
  gap_fill_alpha_threshold = 0.25,
  color = "black",
  alpha = 1,
  pad = 0,
  composite = TRUE,
  filename = NULL,
  preview = FALSE
)

Arguments

image	Default NULL. Image whose alpha channel will be used as the mask. If mask is supplied, image is only used for metadata.
mask	Default NULL. Optional logical or numeric matrix to use as the outline mask instead of image alpha.
expand	Default 0. Number of pixels to expand the mask.
edge_softness	Default 0.1. Width of the softened halo edge transition, in pixels.
blur	Default 0. Gaussian blur standard deviation applied to the final outline alpha.
gap_fill	Default 1. Maximum alpha gap width, in pixels, to bridge in the expanded outline alpha. This fills border-connected breaks and notches caused by discrete distance quantization. Set to 0 to disable.
gap_fill_alpha_threshold	Default 0.25. Alpha threshold used to classify border gaps. Gap filling only modifies pixels below this threshold that are connected to the image exterior; enclosed interior holes surrounded by pixels at or above this threshold are left unchanged.
color	Default "black". Outline color.
alpha	Default 1. Overall outline alpha multiplier.
pad	Default 0. Padding in pixels before computing the outline. If NULL, padding is computed from expand, edge_softness, and blur.
composite	Default TRUE. If TRUE and image is supplied, composite the outline below the original image. Set to FALSE to return the outline alone.
filename	Default NULL. File to save the image to. If NULL and preview = FALSE, returns the output image.
preview	Default FALSE. If TRUE, display the outline image.

Value

A rayimg RGBA output image with a padding attribute.

Examples

txt = render_text_image("\U0001F409",  size = 120, background_alpha = 0)
render_alpha_outline(txt, expand = 2, blur = 1, color = "purple") |>
 plot_image()

#Make a rainbow outline 
render_alpha_outline(txt, expand = 2, blur = 0.1, color = "darkgreen") |>
 render_alpha_outline(expand = 2, blur = 0.1, color = "yellow") |>
 render_alpha_outline(expand = 2, blur = 0.1, color = "orange") |>
 render_alpha_outline(expand = 2, blur = 0.1, color = "red") |>
 render_alpha_outline(expand = 2, blur = 0.1, color = "purple") |>
 render_alpha_outline(expand = 2, blur = 0.1, color = "blue") |>
 plot_image()

rayimage documentation built on June 12, 2026, 5:06 p.m.