The magick package: Advanced Image-Processing in R
The magick package provide a modern and simple toolkit for image processing in R. It wraps the ImageMagick STL which is the most comprehensive open-source image processing library available today.
The ImageMagick library has an overwhelming amount of functionality. Magick exposes a decent subset of it, but it is impossible to document everything in detail. This article introduces some basic concepts and examples to get started.
Installing magick
On Windows or macOS the package is most easily installed via CRAN.
The binary CRAN packages work out of the box and have most important
features enabled. Use magick_config to see which features
and formats are supported by your version of ImageMagick.
## Linking to ImageMagick 6.9.12.98
## Enabled features: fontconfig, freetype, fftw, heic, lcms, pango, raw, webp, x11
## Disabled features: cairo, ghostscript, rsvg## Using 4 threads## List of 24
## $ version :Class 'numeric_version' hidden list of 1
## ..$ : int [1:4] 6 9 12 98
## $ modules : logi TRUE
## $ cairo : logi FALSE
## $ fontconfig : logi TRUE
## $ freetype : logi TRUE
## $ fftw : logi TRUE
## $ ghostscript : logi FALSE
## $ heic : logi TRUE
## $ jpeg : logi TRUE
## $ lcms : logi TRUE
## $ libopenjp2 : logi TRUE
## $ lzma : logi TRUE
## $ pangocairo : logi TRUE
## $ pango : logi TRUE
## $ png : logi TRUE
## $ raw : logi TRUE
## $ rsvg : logi FALSE
## $ tiff : logi TRUE
## $ webp : logi TRUE
## $ wmf : logi TRUE
## $ x11 : logi TRUE
## $ xml : logi TRUE
## $ zero-configuration: logi FALSE
## $ threads : int 4Build from source
On Linux you need to install the ImageMagick++ library: on Debian/Ubuntu this is called libmagick++-dev:
sudo apt-get install libmagick++-devOn Fedora or CentOS/RHEL we need ImageMagick-c++-devel:
sudo yum install ImageMagick-c++-develTo install from source on macOS you need either
imagemagick@6 or imagemagick from
homebrew.
brew install imagemagick@6Unfortunately the current imagemagick@6 configuration on
homebrew disables a bunch of features, including librsvg and fontconfig.
Therefore the quality of fonts and svg rendering might be suboptimal.
The is not a problem for the CRAN binary package.
Image IO
What makes magick so magical is that it automatically converts and
renders all common image formats. ImageMagick supports dozens of formats
and automatically detects the type. Use
magick::magick_config() to list the formats that your
version of ImageMagick supports.
Read and write
Images can be read directly from a file path, URL, or raw vector with
image data with image_read. The image_info
function shows some meta data about the image, similar to the
imagemagick identify command line utility.
library(magick)
tiger <- image_read_svg('http://jeroen.github.io/images/tiger.svg', width = 350)
print(tiger)## format width height colorspace matte filesize density
## 1 PNG 350 350 sRGB TRUE 0 72x72
We use image_write to export an image in any format to a
file on disk, or in memory if path = NULL.
If path is a filename, image_write returns
path on success such that the result can be piped into
function taking a file path.
Converting formats
Magick keeps the image in memory in its original format. Specify the
format parameter image_write to convert to
another format. You can also internally convert the image to another
format earlier, before applying transformations. This can be useful if
your original format is lossy.
## format width height colorspace matte filesize density
## 1 PNG 350 350 sRGB TRUE 0 72x72Note that size is currently 0 because ImageMagick is lazy (in the good sense) and does not render until it has to.
Preview
IDE’s with a built-in web browser (such as RStudio) automatically display magick images in the viewer. This results in a neat interactive image editing environment.
Alternatively, on Linux you can use image_display to
preview the image in an X11 window. Finally image_browse
opens the image in your system’s default application for a given
type.
Another method is converting the image to a raster object and plot it on R’s graphics display. However this is very slow and only useful in combination with other plotting functionality. See #raster below.
Transformations
The best way to get a sense of available transformations is walk
through the examples in the ?transformations help page in
RStudio. Below a few examples to get a sense of what is possible.
Cut and edit
Several of the transformation functions take an geometry
parameter which requires a special syntax of the form
AxB+C+D where each element is optional. Some examples:
image_crop(image, "100x150+50"): crop outwidth:100pxandheight:150pxstarting+50pxfrom the leftimage_scale(image, "200"): resize proportionally to width:200pximage_scale(image, "x200"): resize proportionally to height:200pximage_fill(image, "blue", "+100+200"): flood fill with blue starting at the point atx:100, y:200image_border(frink, "red", "20x10"): adds a border of 20px left+right and 10px top+bottom
The full syntax is specified in the Magick::Geometry documentation.
## format width height colorspace matte filesize density
## 1 PNG 220 445 sRGB TRUE 73494 72x72
# Add 20px left/right and 10px top/bottom
image_border(image_background(frink, "hotpink"), "#000080", "20x10")
