13.1 Crop plots

The chunk hook knitr::hook_pdfcrop() can be used to crop PDF and other types of plot files, i.e., remove the extra margins in plots. To enable it, set this hook via knit_hooks$set() in a code chunk, and turn on the corresponding chunk option, e.g.,

  1. knitr::knit_hooks$set(crop = knitr::hook_pdfcrop)

Then you can use the chunk option crop = TRUE to crop plots in a code chunk.

The hook hook_pdfcrop() calls the external program pdfcrop to crop PDF files. This program often comes with a LaTeX distribution (e.g., TeX Live or MiKTeX). You can check if it is available in your system via:

  1. # if the returned value is not empty, it is available
  2. Sys.which("pdfcrop")
  1. ##                  pdfcrop 
  2. ## "/usr/local/bin/pdfcrop"

If you are using the LaTeX distribution TinyTeX (see Section 1.2), and pdfcrop is not available in your system, you may install it via tinytex::tlmgr_install('pdfcrop').

For non-PDF plot files such as PNG or JPEG files, this hook function calls the R package magick (Ooms 2020) for cropping. You need to make sure this R package has been installed. Figure 13.1 shows a plot that is not cropped, and Figure 13.2 shows the same plot but has been cropped.

A plot that is not cropped.

FIGURE 13.1: A plot that is not cropped.

A plot that is cropped.

FIGURE 13.2: A plot that is cropped.

References

———. 2020. Magick: Advanced Graphics and Image-Processing in r. https://CRAN.R-project.org/package=magick.