Emacs can display a number of different image formats; some of them
are supported only if particular support libraries are installed on
your machine. In some environments, Emacs can load image
libraries on demand; if so, the variable
can be used to modify the set of known names for these dynamic
libraries (though it is not possible to add new image formats).
The supported image formats include XBM, XPM (this requires the
libXpm version 3.4k and
libz), GIF (requiring
libungif 4.1.0), PostScript, PBM, JPEG (requiring the
libjpeg library version v6a), TIFF (requiring
v3.4), PNG (requiring
libpng 1.0.2), and SVG (requiring
You specify one of these formats with an image type symbol. The image
type symbols are
This variable contains a list of those image type symbols that are potentially supported in the current configuration. Potentially here means that Emacs knows about the image types, not necessarily that they can be loaded (they could depend on unavailable dynamic libraries, for example).
To know which image types are really available, use
This in an alist of image types vs external libraries needed to display them.
Each element is a list
...), where the car is a supported image format from
image-types, and the rest are strings giving alternate filenames for the corresponding external libraries to load.
Emacs tries to load the libraries in the order they appear on the list; if none is loaded, the running session of Emacs won't support the image type.
xbmdon't need to be listed; they're always supported.
This variable is ignored if the image libraries are statically linked into Emacs.
This function returns non-
nilif image type type is available, i.e., if images of this type can be loaded and displayed in Emacs. type should be one of the types contained in
For image types whose support libraries are statically linked, this function always returns
t; for other image types, it returns
tif the dynamic library could be loaded,