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Plot the pixels of a transformed image

Source: R/plot_pixels.R
plot_pixels.Rd

This function is a wrapper for function points() in package graphics for plotting the pixels of a transformed rgb image on the triangular diagram previously created by plot_rgb_plane().

Usage

plot_pixels(image_rgb, x_axis, y_axis, ...)

Arguments

image_rgb

an object produced by read_image().

x_axis

a character string indicating which colour variable use as x.

y_axis

a character string indicating which colour variable use as y.

...

additional graphical parameters, mainly to set the colour (col) of the points.

Value

The function does not return any value.

Details

It is advantageous to specify a colour such as "#00000005" which is black but almost transparent. In this way a kind of density plot is created because the clustering of points creates areas of darker colour. Note that a colour without specific transparency information defaults to an opaque colour, so "#000000" is the same as "#000000ff". The colours can be specified in any form understandable by grDevices::col2rgb, but the hexadecimal string allows setting the colour transparency and it is the preferred style. Note also that the points are plotted using pch = ".", as any other symbol would clutter the graph.

Warning: plotting several million points in an R graph is a slow process. Be patient or reduce the size of the images as much as possible. Having a nice smartphone with a petapixel camera sensor is good for artistic purposes, but not always for efficient scientific work.

See also

plot_rgb_plane, col2rgb

Examples


# Plotting the pixels of the example image included in this package
ivy_oak_rgb <- read_image(system.file("extdata", "IvyOak400x300.JPG",
                                       package = "pixelclasser"))
plot_rgb_plane("g", "b")
plot_pixels(ivy_oak_rgb, "g", "b", col = "#00000005")