Knitr changes Image Size

Question

When using RMarkdown + Knitr to make an HTML output of my code/plots, the plot images always appear as expected in RStudio with the correct width/height sizes specified in the chunk options, but if I then use Knitr to put everything together in an HTML document, the plots are all resized to a smaller default it seems.

Viewing each plot separately in a new tab shows their large size as desired but why can't this be the way they are shown in the HTML. Any setting I can change for this?

Answer 1

There is a difference between fig.width and out.width, and likewise between fig.height and out.height. The fig.* control the size of the graphic that is saved, and the out.* control how the image is scaled in the output.

For example, the following .Rmd file will produce the same graphic twice but displayed with different width and height.

---
title: "Example graphic"
---

```{r echo = FALSE, fig.width = 14, fig.height = 9, out.width = "588", out.height = "378"}
library(ggplot2)
ggplot(mpg, aes(x = year, y = cyl)) + geom_point()
```

```{r echo = FALSE, fig.width = 14, fig.height = 9, out.width = "1026", out.height = "528"}
library(ggplot2)
ggplot(mpg, aes(x = year, y = cyl)) + geom_point()
```