plotZmap: Plots a Z-map

In rcicr: Reverse-Correlation Image-Classification Toolbox

Plots a Z-map

Description

Plots a z-map: a matrix of z-scores drawn over a background image.

Usage

plotZmap(
  zmap,
  bgimage = "",
  sigma,
  threshold = 3,
  mask = NULL,
  decoration = TRUE,
  targetpath,
  filename = "zmap",
  size = 512,
  ...,
  pointsize = 12
)

Arguments

zmap	Matrix of z-scores. Must have the same dimensions as bgimage.
bgimage	Greyscale image matrix to draw behind the z-map, normally the base image or the final CI. Without it, only the z-map is drawn.
sigma	Sigma of the smoothing applied to the CI to create the z-map, shown in the decoration.
threshold	Threshold z-score (default: 3). Z-scores below it are not drawn on the z-map.
mask	Optional mask: a binary matrix the size of zmap (0 or FALSE = masked, 1 or TRUE = kept), or the path to a black-and-white PNG image (black = masked, white = kept). This is the same convention as generateCI()'s mask, so one mask works for both. Earlier versions of this documentation described the matrix the wrong way round.
decoration	Boolean: draw the z-map with margins, a caption (sigma, threshold) and a scale (default: TRUE).
targetpath	Directory to save the z-map PNG to. Required, since writing that file is this function's purpose; there is no default. The directory is created if it does not exist; to just try the function out, use tempdir().
filename	Optional file name for the z-map PNG.
size	Width and height of the PNG image, in pixels (default: 512).
...	Further arguments passed to graphics::image. Used only when decoration = TRUE.
pointsize	Text size of the decoration, in points (default: 12, the graphics device's own default). Margins are measured in lines of text, so this also sets how much of the image the decoration takes up. The minimum image size is fixed in inches, so in pixels it depends on the device's resolution: roughly 12.3 * pointsize pixels at 72 ppi (Linux, macOS) and 16.4 * pointsize at 96 ppi (Windows), about 160 and 200 pixels at the default. Below that, plotZmap() stops and names the minimum for your device. A lower pointsize fits a decorated z-map onto a small image, at the cost of a smaller map: the margins shrink but the labels still need room. Ignored when decoration = FALSE, which has no margins and works at any size.

Details

Takes a matrix of z-scores, such as the zmap that generateCI returns, and optionally a background image matrix, and writes the z-map as a PNG. Further arguments are passed to graphics::image; for example, col sets a different colour palette. Versions up to and including 1.2.3 passed them to the raster package's plot method instead. col works the same in both, but arguments specific to that method are no longer understood.

Value

Nothing; the z-map is written as a PNG.

Reproducibility across platforms

The z-scores are ordinary R arithmetic and do not depend on your operating system; nor do classification images, scaling or informational value. The PNG this function writes does: it is drawn through a graphics device, and devices differ between platforms in colour management and in whether they write an alpha channel. The same z-map rendered on Linux and on macOS gives figures that look identical but are not byte-identical. macOS renders a mid-grey background at roughly 0.573, where the cairo device gives 0.502.

So to check that an analysis reproduces, compare the numbers, not the rendered figures. A z-map PNG that differs pixel for pixel on a colleague's machine is not a different result, and regenerating figures on another platform is safe.

This applies only to plotZmap(), the one function in the package that opens a graphics device. Every other PNG rcicr writes (stimuli, classification images, autoscaled classification images) comes straight from the pixel array via png::writePNG().

Examples

set.seed(1)
zmap <- matrix(rnorm(64, sd = 5), 8, 8)
plotZmap(zmap, sigma = 3, threshold = 3, decoration = FALSE,
         targetpath = tempdir(), size = 200)

rcicr documentation built on Sept. 27, 2026, 5:07 p.m.