An image descriptor is a list which specifies the underlying
data for an image, and how to display it. It is typically used as the
value of a
display overlay or text property (see Other Display Specs); but See Showing Images, for convenient helper
functions to insert images into buffers.
Each image descriptor has the form
(image . props
where props is a property list of alternating keyword symbols
and values, including at least the pair
:type type that
specifies the image type.
The following is a list of properties that are meaningful for all image types (there are also properties which are meaningful only for certain image types, as documented in the following subsections):
:file, but not both.
For most image types, the value of a
:data property should be a
string containing the image data. Some image types do not support
:data; for some others,
:data alone is not enough, so
you need to use other image properties along with
the following subsections for details.
)of such numbers. If it is a pair, x specifies how many pixels to add horizontally, and y specifies how many pixels to add vertically. If
:marginis not specified, the default is zero.
If ascent is a number, that percentage of the image's height is used for its ascent.
If ascent is
center, the image is vertically centered
around a centerline which would be the vertical centerline of text drawn
at the position of the image, in the manner specified by the text
properties and overlays that apply to the image.
If this property is omitted, it defaults to 50.
(x-1/y-1 x/y-1 x+1/y-1 x-1/y x/y x+1/y x-1/y+1 x/y+1 x+1/y+1)
The resulting pixel is computed from the color intensity of the color resulting from summing up the RGB values of surrounding pixels, multiplied by the specified factors, and dividing that sum by the sum of the factors' absolute values.
Laplace edge-detection currently uses a matrix of
(1 0 0 0 0 0 0 0 -1)
Emboss edge-detection uses a matrix of
( 2 -1 0 -1 0 1 0 1 -2)
), build a clipping mask for the image, so that the background of a frame is visible behind the image. If bg is not specified, or if bg is
t, determine the background color of the image by looking at the four corners of the image, assuming the most frequently occurring color from the corners is the background color of the image. Otherwise, bg must be a list
(red green blue
)specifying the color to assume for the background of the image.
If mask is
nil, remove a mask from the image, if it has
one. Images in some formats include a mask which can be removed by
An image map is an alist where each element has the format
(area id plist
). An area is specified
as either a rectangle, a circle, or a polygon.
A rectangle is a cons
(rect . ((x0
) . (x1
which specifies the pixel coordinates of the upper left and bottom right
corners of the rectangle area.
A circle is a cons
(circle . ((x0
) . r
which specifies the center and the radius of the circle; r may
be a float or integer.
A polygon is a cons
(poly . [x0 y0 x1 y1
where each pair in the vector describes one corner in the polygon.
When the mouse pointer lies on a hot-spot area of an image, the
plist of that hot-spot is consulted; if it contains a
property, that defines a tool-tip for the hot-spot, and if it contains
pointer property, that defines the shape of the mouse cursor when
it is on the hot-spot.
See Pointer Shape, for available pointer shapes.
When you click the mouse when the mouse pointer is over a hot-spot, an
event is composed by combining the id of the hot-spot with the
mouse event; for instance,
[area4 mouse-1] if the hot-spot's
This function returns
tif image spec has a mask bitmap. frame is the frame on which the image will be displayed. frame
nilor omitted means to use the selected frame (see Input Focus).