measuresil {gdi}

Take pixel-by-pixel measurements of a silhouette in jpeg or png format for use with the gdi function.

Description

Take pixel-by-pixel measurements of a silhouette in jpeg or png format for use with the gdi function.

Usage

measuresil(
  image_file,
  threshold = 0.5,
  channel = 4,
  method = "greater",
  align = "h",
  return = "diameters"
)

Arguments

image_file

Image to be read. Images can be jpeg or png files, or a previously read image saved as an object in R.

threshold

Reference value for color criterium after which pixels that are part of the silhouette are differentiated from the background.

channel

Color channel to which to apply the threshold criterium. Default is 4 (alpha channel of rgba image). Channel setting needs to be adjusted depending on the color mode of the image used (e.g. there are two channels to choose from in a greyscale image with transparency, and 3 in an rgb image without transparency, or 4 in a full rgba image).

method

Method for determining which pixels to count. Default "greater" counts pixels with value greater than threshold (e.g. higher opacity, in the case of an alpha channel). "less" counts pixels with a value less than the threshold. "not" counts all pixels not precisely matching threshold. Any other character string results in only pixels exactly matching the value given as threshold being counted.

align

Indicate whether the silhouette long axis is aligned horizontally (setting "h", default), or vertically (any other parameter setting).

return

Setting for what to return, default setting ("diameters") returns a single vector containing the diameters, any other setting returns a data frame containing centers and diameters.

Value

A numeric vector giving the measurements of the silhouette

Examples

fdir <- system.file(package="gdi")
lat <- measuresil(file.path(fdir,"exdata","lat.png"))