(R-data.info)Image files

---

Next: Connections Prev: Binary files Up: Top

---

Enter node , (file) or (file)node

6 Image files
*************

A particular class of binary files are those representing images, and a
not uncommon request is to read such a file into R as a matrix.

   There are many formats for image files (most with lots of variants),
and it may be necessary to use external conversion software to first
convert the image into one of the formats for which a package currently
provides an R reader.  A versatile example of such software is
ImageMagick and its fork GraphicsMagick.  These provide command-line
programs 'convert' and 'gm convert' to convert images from one format to
another: what formats they can input is determined when they are
compiled, and the supported formats can be listed by e.g. 'convert -list
format'.

   Package *pixmap* (https://CRAN.R-project.org/package=pixmap) has a
function 'read.pnm' to read 'portable anymap' images in PBM
(black/white), PGM (grey) and PPM (RGB colour) formats.  These are also
known as 'netpbm' formats.

   Packages *bmp* (https://CRAN.R-project.org/package=bmp), *jpeg*
(https://CRAN.R-project.org/package=jpeg) and *png*
(https://CRAN.R-project.org/package=png) read the formats after which
they are named.  See also packages *biOps*
(https://CRAN.R-project.org/package=biOps) and *Momocs*
(https://CRAN.R-project.org/package=Momocs), and Bioconductor package
*EBImage*.

   TIFF is more a meta-format, a wrapper within which a very large
variety of image formats can be embedded.  Packages *rtiff*
(https://CRAN.R-project.org/package=rtiff) and *tiff*
(https://CRAN.R-project.org/package=tiff) can read some of the
sub-formats (depending on the external 'libtiff' software against which
they are compiled).  There some facilities for specialized sub-formats,
for example in Bioconductor package *beadarray*.

   Raster files are common in the geographical sciences, and package
*rgdal* (https://CRAN.R-project.org/package=rgdal) provides an interface
to GDAL which provides some facilities of its own to read raster files
and links to many others.  Which formats it supports is determined when
GDAL is compiled: use 'gdalDrivers()' to see what these are for the
build you are using.  It can be useful for uncommon formats such as JPEG
2000 (which is a different format from JPEG, and not currently supported
in the macOS nor Windows binary versions of *rgdal*
(https://CRAN.R-project.org/package=rgdal)).