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Compute the colors and alpha values of the shells.

Source: R/volvis_shells.R
shell.palette.Rd

The palette defines how the shells look: their colors and how transparent they are, from the outermost to the innermost shell. Three palettes are available:

  • 'grey_context' (the default): all shells but the innermost one are grey (like the semi-transparent cortex in vis.subcortical.region.values is), and the innermost shell is rendered in a warm color and fully opaque. This gives the impression of looking at a structure inside a translucent head, and it makes a single feature stand out, at the price of hiding the level of the inner shells.

  • 'sequential': a single hue, getting lighter and more opaque towards the innermost shell. Useful to emphasize the nested structure, and to avoid the colorful look of 'viridis'.

  • 'viridis': the full viridis ramp, with the outer shells dark and very transparent and the inner ones bright. This is the most colorful option, and it encodes the iso-level in the color.

Usage

shell.palette(palette = "grey_context", num_shells = 4L, alpha_range = NULL)

Arguments

palette

character string, the name of the palette: one of 'grey_context', 'sequential' or 'viridis'.

num_shells

positive integer, the number of shells.

alpha_range

numerical vector of length 2 or NULL. The alpha value of the outermost and of the innermost (non-opaque) shell. If NULL, the default range of the palette is used.

Value

a named list with the entries 'colors' (character vector, one color per shell) and 'alphas' (numerical vector, one alpha value per shell).