scaleBar2: Add Scale Bar to Image

In ornelles/EBImageExtra: Helper Functions for EBImage

Add Scale Bar to Image

Description

Place a single horizontal scale bar of length distance as per scale factor scale with unit of measure units.

Usage

scaleBar2(
  x,
  y = NULL,
  distance,
  scale,
  units = "µm",
  col = "white",
  col.text,
  cex = 3/4,
  adj = c(0.5, -0.5),
  col.line,
  lwd = 1,
  lend = 1,
  xpd = NA,
  ...
)

Arguments

x, y	Central coordinates of the scale bar in pixels
distance	Distance represented by the scale bar in microns
scale	Image scale as µm per pixel
units	Unit of measure, default of "µm". Use NA to exclude the label
col	Default color (white) for col.text and col.line
col.text, cex, adj, xpd, ...	Parameters passed to the text function used to add the label
col.line, lwd, lend	Parameters passed to the lines function used to draw the horizontal scale bar

Details

This is a utility to place a labeled scale bar on a raster image. A default label will include the distance in µm if unit is not NA. The label is centered at the position specified by x,y according to adj. The default value for adj of c(0.5,-0.5) centers the label and places it 0.5 character widths above x,y.

The x,y coordinates can be passed in a plotting structure appropriate for xy.coords. This function attempts to parse distance and scale from the remaining arguments if they are not named and if x is a list with components named "x" and "y". This allows one to interactively place a scale bar with a function call such as in the following example. In this example, scale is the scale factor as "µm per pixel."

This call will place a labeled 25 µm scale bar on the image as per the value in scale

> scaleBar(locator(), 25, scale)

Note that this is not a vectorized function. Only the last value of (x, y) will be used to place the scale bar. This allows multiple clicks to locator() to get the position just right with only the last click being used.

Micrometers-per-pixels calibration values for the Nikon TE300 at 1x1 binning with the QImaging camera are:

Objective   scale factor
 20X ELWD    0.3228
 40X ELWD    0.1624
 60X ELWD    0.1062
 60X Apo     0.1064
100X Apo     0.0640
  4X Apo     1.613 (estimated)

Value

This function is called for side effects but the location is returned invisibly as a list.

ornelles/EBImageExtra documentation built on June 14, 2025, 8:59 p.m.