Graphics output

Andrew Irwin, a.irwin@dal.ca

2024-04-02

Plan

• Kinds of graphics

• How to describe the size of a graphic

• Knitted documents and separate files

Starting figure

Kinds of graphics

• Vector graphics (pdf, svg)

• Bitmapped or raster graphics (png, jpeg)

• Why does it matter?

  • File sizes

  • Quality when printed

  • Appearance on screen

Overview

• Device types: png, ragg, jpeg, svg, pdf

• Size: fig.height, fig.width (in inches, default 7), and fig.asp (aspect ratio: height / width)

• Display size: out.width, out.height (in percentage of display area, e.g., ‘70%’)

• Resolution: dpi (dots per inch; 96-250 on screen, 300-600 when printed)

• Alignment: fig.align = left, right, center

Chunk options

R markdown:

```{r fig.height = 5, fig.asp = 0.6}
# code for plot here
```

Quarto document (as above, or…)

#| fig.height: 5
#| fig.asp: 0.5
# code for plot here

PNG example

Chunk options: fig.width = 6, fig.asp = 0.65, fig.align="center", out.width = '70%', dev = 'png'

Higher resolution PNG example

Chunk options: dev='png', dpi=150

RAGG example

Chunk options: dev='ragg_png', dpi = 150

Fails with PNG

Chunk options: dev='png', dpi = 150

JPEG example

Chunk options: dev='jpeg', dpi = 150

SVG example

Chunk options: dev='svglite'

Creating standalone files

Use ggsave:

ggsave("test-plot.pdf", p1, height = 4, width = 6)
ggsave("test-plot.png", p1, dpi = 400)