png_ggsized: Save ggplot to correctly-shaped PNG

In infotroph/DeLuciatoR: Make R Plots Match DeLucia Publication Specs

Description

When a ggplot has a fixed panel aspect ratio, it can be a pain to find the right dimensions for the whole plot (including axes, margins, legends, etc) when saving it to a fixed-size graphical device. png_ggized takes a ggplot object and saves it as the largest PNG that fits inside the specified maximum height and width.

DEPRECATED: Use ggsave_fitmax instead; it supports more output formats and is more flexible. If you are updating old code, notice that the arguments to ggsave_fitmax are named and ordered differently than those to png_ggsized.

Usage

	png_ggsized(ggobj, filename, 
		maxheight=4, maxwidth=4,
		res=300, units="in", ...)

Arguments

ggobj	A ggplot or gtable object.
filename	Name for the output image; see png.
maxheight, maxwidth	Numeric, giving argest allowable dimensions of the plot. The final image will exactly match one of these and will not exceed the other.
units	Character, giving units for the dimensions. Must be recognized by both png and grid::convertUnit, so possible values are probably limited to "in", "cm", "mm". Note especially that "px" does not work.
res	Numeric. The nominal resolution, in ppi, for the outpuf file; see png.
...	Other arguments passed to png.

Details

This is a convenience function that wraps three distinct steps: Lookng up the plot dimensions using get_dims, opening a new PNG using png, then writing the image with a simple plot(ggobj). If you need more flexibility in any of these steps, skip this wrapper and use them directly; see the examples in get_dims for an example.

The dimension lookup was motivated by the difficulty of predicting image height & width when the panels have a fixed aspect ratio, but this wrapper should work as a one-call plotting command for plots with unconstrained ratios as well. Please report any that don't work.

Note

Converting pixel dimensions into nominal physical dimensions requires that everyone involved agree what pixel-per-inch resolution they are using, but some PNG viewers ignore the embedded resolution and report physical dimensions from their own assumed ppi. This function can't fix that, but it does use the right pixel dimensions for the resolution you specify.

Author(s)

Chris Black <[e-mail]>

Examples

## Not run: 
a=ggplot(mtcars, aes(wt,mpg))+geom_point()+theme(aspect.ratio=0.75)

# Saves a.png at 3144 x 2400 px 
# == (nominally!) 10.48 x 8 inches at 300 ppi.
png_ggized(a, filename="a.png", maxheight=8, maxwidth=12)

# Saves aa.png at 1172 x 900 px
# == 7.8 x 6 inches at 150 ppi... or 3.9 x 3 inches at 300 ppi, or...
png_ggsized(a, filename="aa.png", maxheight=6, maxwidth=9, res=150)

## End(Not run)

infotroph/DeLuciatoR documentation built on May 30, 2020, 10:28 p.m.