Render Alpha Outline

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.

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()