imagedata (db.imagedata)
imagedata — Pointer to external image data.
Synopsis
info
? (db.titleforbidden.info)
Attributes
Additional attributes:
- align (enumeration)
- “center”
- “char”
- “justify”
- “left”
- “right”
- contentdepth
- contentwidth
- depth
- Each of:
- format
- Exactly one of:
- fileref (anyURI)
- entityref (ENTITY)
- scale (positiveInteger)
- scalefit (enumeration)
- “0”
- “1”
- valign (enumeration)
- “bottom”
- “middle”
- “top”
- width
Required attributes are shown in bold.
Description
This element points to an external entity containing graphical image data.
Processing expectations
Render the image. May be formatted inline or as a displayed block, depending on context.
There are two ways to provide content for
imagedata
: entityref
or fileref
. It is best to use only one of
these methods; however, if multiple sources are provided, entityref
will be
used in favor of fileref
.
The imagedata
provides a selection of
attributes that can be used to control how the image is rendered.
These attributes define two rectangles, the viewport
area and the content area, and how
these rectangles are related to each other. The intrinsic
size of the image is a third rectangle that sometimes
influences the way an image is rendered.
It is important to understand the distinction between these three areas. When rendering an image, the viewport area defines the space reserved in the flow of content for the image. If a 6in × 4in viewport area is specified, that’s how much space will be reserved for the image, independent of the actual size of the rendered image. The content area defines the actual size of the rendered image, independent of the intrinsic size of the image. The intrinsic size of the image is its actual, real size.
DocBook provides three mutually exclusive mechanisms for specifying the content area of an image: it can be specified directly, it can be specified by selecting a scale factor, or it can be specified to be the same size as the viewport area.
Finally, DocBook provides two attributes, align
and valign
, to specify the alignment of the
content area within the viewport area.
DocBook provides no mechanism for specifying how an image should be rendered if the content area exceeds the viewport area in either or both dimensions. Implementations are free to perform clipping, allow the image to overflow, and/or generate errors.
Units of measure
The sizes of the viewport area and the content area are defined in terms of lengths (width and depth).
Lengths must be expressed as a decimal value followed immediately by an optional unit of measure or a percentage. Six and one eighth inches, for example, must be expressed as “6.125in”. It is an error to put a space or other punctuation between the decimal value and the unit of measure.
Examples of common units of measure include:
pt | Points (1/72 of an inch) |
cm | Centimeters |
mm | Millimeters |
in | Inches |
pc | Picas (1/6 of an inch) |
px | Pixels |
em | Ems |
If no unit of measure is provided, px
is
assumed. Note that pixels have no universally accepted absolute size
and ems are relative units of measure. Implementations may define
pixel sizes differently and stylesheets may or may not be able to
determine the current font size in order to correctly calculate the
absolute size of an em. It is best to avoid these units of
measure.
Percentages are expressed as a decimal value followed
immediately by a %
sign.
Specifying the viewport area
The viewport area is specified by the width
and depth
attributes.
If neither width nor depth is specified, an implementation is free to choose defaults. These defaults may be influenced by context. For example, when rendering an inline graphic, the viewport area often defaults to the size of the content area. For block graphics, the width often defaults to the column width while the depth defaults to the depth of the content area.
If only one of width or depth is specified, an implementation is free to choose a default for the other dimension.
Viewport area dimensions expressed as a percentage are a
percentage of the available area. For example, a width of
50%
when an implementation is rendering in a
column 6in
wide is equivalent to specifying a
width of 3in
.
Percentages must be used with care. Some media are unbounded in one or more directions (e.g., web pages are generally unbounded in depth). Specifying a percentage of an unbounded dimension is undefined. Implementations may choose arbitrary defaults or may generate errors.
Specifying the content area
The content area is specified by the contentwidth
and contentdepth
attributes.
If neither content width nor content depth is specified, an
implementation is expected to render the image at its intrinsic size
(unless scaling or scaling to fit is requested). If only one of
content width or content depth is specified, an implementation is
expected to choose a default for the other dimension such that the
image is scaled proportionally. For example, if an image has an
intrinsic size of one square inch and the content width is specified
as 2in
, the content depth must default to
2in
.
Content area dimensions expressed as a percentage are a percentage of the intrinsic size of the image.
Percentages must be used with care. Some implementations may be unable to determine the intrinsic size of an image and will therefore be forced to make compromises. Implementations may choose arbitrary values or may generate errors if the intrinsic size cannot be obtained.
Scaling
Scaling can be specified in two ways: with the scale
attribute or with the scalefit
attribute.
If scale
is specified, it must be a
positive integer. It is always interpreted to be a percentage value,
where 100
represents 100%.
The legal values of scalefit
are 0
(false) or 1
(true). If scaling to fit is
requested, the content area is scaled until
either the content width is the same as the
viewport width (and the content depth is less than or equal to the
viewport depth) or the content depth is the
same as the viewport depth (and the content width is less than or
equal to the viewport width), whichever comes first. In other words,
scaling to fit never causes anamorphic scaling; it simply scales the
image as large as possible without overflowing the bounds of the
viewport area.
Specification of content area, scaling, and scaling to fit are
mutually exclusive. If a content area (contentwidth
, contentdepth
, or both) is specified,
both scaling and scaling to fit are ignored. If
the content area is not specified and both scaling and scaling to
fit are specified, scalefit
is
ignored.
In order to achieve a level of backward compatibility with
previous versions of DocBook (which did not have attributes for
specifying a content area) while maintaining coherent semantics, the
default value of scalefit
depends on other attributes.
Viewport area | Content area | scalefit default |
---|---|---|
Unspecified | Unspecified | Irrelevant |
Specified | Unspecified | 1 |
Unspecified | Specified | 0 |
Specified | Specified | 0 |
If a viewport area is specified (and neither a content area
nor scaling is specified) and scalefit
is explicitly
0
, the viewport area specification must be
ignored, and the image must not be resized.
Alignment
Two alignment attributes are provided: align
and valign
.
If specified, align
indicates how the content area should be aligned horizontally within
the viewport area. If not specified, implementations are free to
choose any default value.
If specified, valign
indicates how the content area should be aligned vertically within
the viewport area. If not specified, implementations are free to
choose any default value.
Examples
If nothing is specified about the size of an image, it is rendered in a content area that is the same as its intrinsic size in a viewport area that is implementation defined:
<imagedata fileref="image.png"/>
If a viewport area is specified, the image is rendered in a content area that is the same as its intrinsic size in the specified viewport area:
<imagedata fileref="image.png" width="6in" depth="5.5in" scalefit="0"/>
If a content area is specified, the image is scaled (possibly anamorphically) to that size and rendered in a viewport area that is implementation defined:
<imagedata fileref="image.png" contentwidth="4in" contentdepth="3in"/>
If a scaling factor is specified, the intrinsic size is scaled uniformly by that amount to obtain the content area which is rendered in a viewport area that is implementation defined:
<imagedata fileref="image.png" scale="300"/>
If a viewport area is specified and scaling to fit is requested, the intrinsic size is scaled (uniformly) as large as possible without extending beyond the bounds of the viewport area which is rendered as specified:
<imagedata fileref="image.png" width="6in" depth="5.5in"/> <!-- note that scalefit="1" is the default in this case -->
If the viewport area and content area are specified, the image is scaled (possibly anamorphically) to the content area size and rendered in the specified viewport area:
<imagedata fileref="image.png" width="6in" depth="5.5in" contentwidth="4in" contentdepth="3in"/>
If the viewport area and a scaling factor are specified, the intrinsic size is scaled uniformly by the scaling factor amount to obtain the content area which is rendered in the specified viewport area:
<imagedata fileref="image.png" width="6in" depth="5.5in" scale="300"/>
Attributes
- align
Specifies the (horizontal) alignment of the image data
Enumerated values: “center” Centered horizontally
“char” Aligned horizontally on the specified character
“justify” Fully justified (left and right margins or edges)
“left” Left aligned
“right” Right aligned
- contentdepth
Specifies the depth of the content rectangle
- contentwidth
Specifies the width of the content rectangle
- depth
Specifies the depth of the element
- entityref
Identifies the location of the data by external identifier (entity name)
- fileref
Indentifies the location of the data by URI
- format
Specifies the format of the data
- scale
Specifies the scaling factor
- scalefit
Determines if anamorphic scaling is forbidden
Enumerated values: “0” False (do not scale-to-fit; anamorphic scaling may occur)
“1” True (scale-to-fit; anamorphic scaling is forbidden)
- valign
Specifies the vertical alignment of the image data
Enumerated values: “bottom” Aligned on the bottom of the region
“middle” Centered vertically
“top” Aligned on the top of the region
- width
Specifies the width of the element
Parents
These elements contain imagedata
: imageobject
.
Children
The following elements occur in imagedata: info
(db.titleforbidden.info).
See Also
imagedata
(db.imagedata.mathml)