SVG filter effects
|Scalable Vector Graphics|
SVG filter effects are effects applied to Scalable Vector Graphics (SVG) files. SVG is an open-standard XML format for two-dimensional vector graphics as defined by the World Wide Web Consortium (W3C). A filter effect consists of a series of graphics operations that are applied to a given source vector graphic to produce a modified bitmapped result.
Filter effects are defined by filter elements. To apply a filter effect to a graphics element or a container element the 'filter' property is set on a given element. Each 'filter' element contains a set of filter primitives as its children. Each filter primitive performs a single fundamental graphical operation (e.g., a Gaussian blur or a lighting effect) on one or more inputs, producing a graphical result. Because most of the filter primitives represent some form of image processing, in most cases the output from a filter primitive is a single RGBA bitmap image (however, it will be regenerated if a higher resolution is called on).
The original source graphic or the result from a filter primitive can be used as input into one or more other filter primitives. A common application is to use the source graphic multiple times. For example, a simple filter could replace one graphic for two by adding a black copy of the original source graphic but offset to create a drop shadow. In effect, there are now two layers of graphics, both with the same original source graphics.
SVG filter primitives
The following table lists the filter primitives available in both SVG 1.0 and SVG 1.1. SVG Tiny does not support filter effects, while SVG Basic supports only those filter primitives shown:
The current draft of the Filter Effects module of SVG 2 adds two further filter primitives:
feCustom (for custom filter effects) and
feDropShadow (for drop shadow). The latter is just a shorthand for a combination of other filter primitives.
Framework for applying a filter
<?xml version="1.0"?> <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"> <svg xmlns="http://www.w3.org/2000/svg" width="4in" height="3in"> <defs> <filter id="AFilter"> <!-- Definition of filter goes here --> </filter> </defs> <text style="filter:url(#AFilter)">a filter applied</text> </svg>
- W3C SVG page specifications, list of implementations
- W3C SVG primer: Filters W3C Primer (draft) chapter and examples concerning filters.