Identify the type of an image using the magic value at the start of the file

Currently works for png, jpeg, BMP, and tiff images. Will seek to start of file if passed a connection. For details of magic values for files, see e.g. http://en.wikipedia.org/wiki/Magic_number_(programming)#Magic_numbers_in_files

image_type(source, Verbose = FALSE)

Arguments

source	Path to file or connection
Verbose	Whether to write a message to console on failure (Default FALSE)

Value

character value corresponding to standard file extension of image format (i.e. jpg, png, bmp, tif) or NA_character_ on failure.

Examples

jpegfile=system.file("img", "Rlogo.jpg", package="jpeg")
image_type(jpegfile)
#> [1] "jpg"
jpeg_pretending_to_be_png=tempfile(fileext = '.png')
file.copy(jpegfile, jpeg_pretending_to_be_png)
#> [1] TRUE
image_type(jpeg_pretending_to_be_png)
#> [1] "jpg"
unlink(jpeg_pretending_to_be_png)