SVG images and their behaviors are defined in XML text files. This means that they can be searched, indexed, scripted, and compressed. As XML files, SVG images can be created and edited with any text editor, but are more often created with drawing software.
This image illustrates the difference between bitmap and vector images. The bitmap image is composed of a fixed set of dots, while the vector image is composed of a fixed set of shapes. In the picture, scaling the bitmap reveals the dots while scaling the vector image preserves the shapes.
Since 2001, the SVG specification has been updated to version 1.1. The SVG Mobile Recommendation introduced two simplified profiles of SVG 1.1, SVG Basic and SVG Tiny, meant for devices with reduced computational and display capabilities. An enhanced version of SVG Tiny, called SVG Tiny 1.2, later became an autonomous Recommendation.
Though the SVG Specification primarily focuses on vector graphics markup language, its design includes the basic capabilities of a page description language like Adobe's PDF. It contains provisions for rich graphics, and is compatible with CSS for styling purposes. SVG has the information needed to place each glyph and image in a chosen location on a printed page. (By contrast, XHTML's primary purpose is to communicate content, not presentation, so XHTML specifies objects to be displayed but not where to place them.) A print-specialized subset of SVG (SVG Print, authored by Canon, HP, Adobe and Corel) is currently[update] a W3C Working Draft.
SVG images, being XML, contain many repeated fragments of text, so they are well suited for lossless data compression algorithms. When an SVG image has been compressed with the industry standard gzip algorithm, it is referred to as an "SVGZ" image and uses the corresponding .svgz filename extension. Conforming SVG 1.1 viewers will display compressed images. An SVGZ file is typically 20 to 50 percent of the original size. W3C provides SVGZ files to test for conformance.
SVG 1.1 became a W3C Recommendation on 14 January 2003. The SVG 1.1 specification is modularized in order to allow subsets to be defined as profiles. Apart from this, there is very little difference between SVG 1.1 and SVG 1.0.
SVG Tiny and SVG Basic (the Mobile SVG Profiles) became W3C Recommendations on 14 January 2003. These are described as profiles of SVG 1.1.
SVG Tiny 1.2 became a W3C Recommendation on 22 December 2008. It was initially drafted as a profile of the planned SVG Full 1.2 (which has since been dropped in favor of SVG 2), but was later refactored as a standalone specification.
SVG 1.1 Second Edition, which includes all the errata and clarifications, but no new features to the original SVG 1.1 was released on 16 August 2011.
SVG 2 will completely rework draft 1.2 with more integration with new web features such as CSS, HTML5 and WOFF.
The MPEG-4 Part 20 standard - Lightweight Application Scene Representation (LASeR) and Simple Aggregation Format (SAF) is based on SVG Tiny. It was developed by MPEG (ISO/IEC JTC1/SC29/WG11) and published as ISO/IEC 14496-20:2006. SVG capabilities are enhanced in MPEG-4 Part 20 with key features for mobile services, such as dynamic updates, binary encoding, state-of-art font representation. SVG was also accommodated in MPEG-4 Part 11, in the Extensible MPEG-4 Textual (XMT) format - a textual representation of the MPEG-4 multimedia content using XML.
Because of industry demand, two mobile profiles were introduced with SVG 1.1: SVG Tiny (SVGT) and SVG Basic (SVGB). These are subsets of the full SVG standard, mainly intended for user agents with limited capabilities. In particular, SVG Tiny was defined for highly restricted mobile devices such as cellphones; it doesn't support styling or scripting. SVG Basic was defined for higher-level mobile devices, such as PDAs.
In 2003, the 3GPP, an international telecommunications standards group, adopted SVG Tiny as the mandatory vector graphics media format for next-generation phones. SVGT is the required vector graphics format and support of SVGB is optional for Multimedia Messaging Service (MMS) and Packet-switched Streaming Service. It was later added as required format for vector graphics in 3GPP IP Multimedia Subsystem (IMS). Neither mobile profile includes support for the full DOM, while only SVG Basic has optional support for scripting, but because they are fully compatible subsets of the full standard, most SVG graphics can still be rendered by devices which only support the mobile profiles.
SVGT 1.2 adds a microDOM (μDOM), styling and scripting.
The SVG 1.1 specification defines 14 functional areas or feature sets:
Simple or compound shape outlines are drawn with curved or straight lines that can be filled in, outlined, or used as a clipping path. Paths have a compact coding. For example M (for 'move to') precedes initial numeric x and ycoordinates and L (line to) precedes a point to which a line should be drawn. Further command letters (C, S, Q, T and A) precede data that is used to draw various Bézier and elliptical curves. Z is used to close a path. In all cases, absolute coordinates follow capital letter commands and relative coordinates are used after the equivalent lower-case letters.
Straight-line paths and paths made up of a series of connected straight-line segments (polylines), as well as closed polygons, circles and ellipses can be drawn. Rectangles and round-cornered rectangles are also standard elements.
Unicode character text included in an SVG file is expressed as XML character data. Many visual effects are possible, and the SVG specification automatically handles bidirectional text (for composing a combination of English and Arabic text, for example), vertical text (as Chinese was historically written) and characters along a curved path (such as the text around the edge of the Great Seal of the United States).
SVG shapes can be filled and/or outlined (painted with a color, a gradient, or a pattern). Fills can be opaque or have any degree of transparency. "Markers" are line-end features, such as arrowheads, or symbols that can appear at the vertices of a polygon.
Colors can be applied to all visible SVG elements, either directly or via 'fill', 'stroke,' and other properties. Colors are specified in the same way as in CSS2, i.e. using names like black or blue, in hexadecimal such as #2f0 or #22ff00, in decimal like rgb(255,255,127), or as percentages of the form rgb(100%,100%,50%).
Gradients and patterns
SVG shapes can be filled or outlined with solid colors as above, or with color gradients or with repeating patterns. Color gradients can be linear or radial (circular), and can involve any number of colors as well as repeats. Opacity gradients can also be specified. Patterns are based on predefined raster or vector graphic objects, which can be repeated in x and/or y directions. Gradients and patterns can be animated and scripted.
Since 2008, there has been discussion among professional users of SVG that either gradientmeshes or preferably diffusion curves could usefully be added to the SVG specification. It is said that a "simple representation [using diffusion curves] is capable of representing even very subtle shading effects" and that "Diffusion curve images are comparable both in quality and coding efficiency with gradient meshes, but are simpler to create (according to several artists who have used both tools), and can be captured from bitmaps fully automatically." The current draft of SVG 2 includes gradient meshes.
Clipping, masking and compositing
Graphic elements, including text, paths, basic shapes and combinations of these, can be used as outlines to define both inside and outside regions that can be painted (with colors, gradients and patterns) independently. Fully opaque clipping paths and semi-transparent masks are composited together to calculate the color and opacity of every pixel of the final image, using alpha blending.
SVG images can interact with users in many ways. In addition to hyperlinks as mentioned below, any part of an SVG image can be made receptive to user interface events such as changes in focus, mouse clicks, scrolling or zooming the image and other pointer, keyboard and document events. Event handlers may start, stop or alter animations as well as trigger scripts in response to such events.
SVG images can contain hyperlinks to other documents, using XLink. URLs of SVG images can specify geometrical transforms in the fragment section.
SVG content can be animated using the built-in animation elements such as <animate>, <animateMotion> and <animateColor>. Content can be animated by manipulating the DOM using ECMAScript and the scripting language's built-in timers. SVG animation has been designed to be compatible with current and future versions of Synchronized Multimedia Integration Language (SMIL). Animations can be continuous, they can loop and repeat, and they can respond to user events, as mentioned above.
As with HTML and CSS, text in SVG may reference external font files, such as system fonts. If the required font files do not exist on the machine where the SVG file is rendered, the text may not appear as intended. To overcome this limitation, text can be displayed in an SVG font, where the required glyphs are defined in SVG as a font that is then referenced from the <text> element.
In accord with the W3C's Semantic Web initiative, SVG allows authors to provide metadata about SVG content. The main facility is the <metadata> element, where the document can be described using Dublin Core metadata properties (e.g. title, creator/author, subject, description, etc.). Other metadata schemas may also be used. In addition, SVG defines <title> and <desc> elements where authors may also provide plain-text descriptive material within an SVG image to help indexing, searching and retrieval by a number of means.
An SVG document can define components including shapes, gradients etc., and use them repeatedly. SVG images can also contain raster graphics, such as PNG and JPEG images, and further SVG images.
This code will produce a green square with a black outline:
The use of SVG on the web was limited by the lack of support in older versions of Internet Explorer (IE). Many web sites that serve SVG images, such as Wikipedia, also provide the images in a raster format, either automatically by HTTPcontent negotiation or by allowing the user directly to choose the file.
Google announced on 31 August 2010 that it had started to index SVG content on the web, whether it is in standalone files or embedded in HTML, and that users would begin to see such content listed among their search results. It was announced on 8 December 2010 that Google Image Search would also begin indexing SVG files. On 28 January 2011, it was discovered that Google was allowing Image Search results to be restricted exclusively to SVG files. This feature was announced officially on 11 February 2011.
Native browser support
Konqueror was the first browser to support SVG in release version 3.2 in February 2004. As of 2011, all major desktop browsers, and many minor ones, have some level of SVG support. Other browsers' implementations are not yet complete; see comparison of layout engines for further details.
Some earlier versions of Firefox (e.g. versions between 1.5 and 3.6), as well as a smattering of other now-outdated web browsers capable of displaying SVG graphics, needed them embedded in <object> or <iframe>elements to display them integrated as parts of an HTML webpage instead of using the standard way of integrating images with <img>. However, SVG images may be included in XHTML pages using XML namespaces.
Opera (since 8.0) has support for the SVG 1.1 Tiny specification while Opera 9 includes SVG 1.1 Basic support and some of SVG 1.1 Full. Opera 9.5 has partial SVG Tiny 1.2 support. It also supports SVGZ (compressed SVG).
Browsers based on the Geckolayout engine (such as Firefox, Flock, Camino, and SeaMonkey) all have had incomplete support for the SVG 1.1 Full specification since 2005. The Mozilla site has an overview of the modules which are supported in Firefox and of the modules which are in progress in the development. Gecko 1.9, included in Firefox 3.0, adds support for more of the SVG specification (including filters).
Internet Explorer 8 and older versions do not support SVG. IE9 (released 14 March 2011) supports the basic SVG feature set. IE10 extended SVG support by adding SVG 1.1 filters.
There are several advantages to native and full support: plugins are not needed, SVG can be freely mixed with other content in a single document, and rendering and scripting become considerably more reliable.
Plug-in browser support
Internet Explorer, up to and including IE8, was the only major browser not to provide native SVG support. IE8 and older require a plug-in to render SVG content. There are a number of plug-ins available to assist, including:
On 5 January 2010, a senior manager of the Internet Explorer team at Microsoft announced on his official blog that Microsoft had just requested to join the SVG Working Group of the W3C in order to "take part in ensuring future versions of the SVG spec will meet the needs of developers and end users," although no plans for SVG support in Internet Explorer were mentioned at that time. Internet Explorer 9 beta supported a basic SVG feature set based on the SVG 1.1 W3C recommendation. Functionality has been implemented for most of the SVG document structure, interactivity through scripting and styling inline and through CSS. The presentation elements, attributes and DOM interfaces that have been implemented include basic shapes, colors, filling, gradients, patterns, paths and text.
SVG Tiny (SVGT) 1.1 and 1.2 are mobile profiles for SVG. SVGT 1.2 includes some features not found in SVG 1.1, including non-scaling strokes, which are supported by some SVG 1.1 implementations, such as Opera, Firefox and WebKit. As shared code bases between desktop and mobile browsers increased, the use of SVG 1.1 over SVGT 1.2 also increased.
Support for SVG may be limited to SVGT on older or more limited smart phones, or may be primarily limited by their respective operating system. Adobe Flash Lite has optionally supported SVG Tiny since version 1.1. At the SVG Open 2005 conference, Sun demonstrated a mobile implementation of SVG Tiny 1.1 for the Connected Limited Device Configuration (CLDC) platform.
Mobiles that use Opera Mobile, as well as the iPhone's built in browser, also include SVG support. However, even though it used the WebKit engine, the Android built-in browser did not support SVG prior to v3.0 (Honeycomb). Prior to v3.0, Firefox Mobile 4.0b2 (beta) for Android was the first browser running under Android to support SVG by default.
The level of SVG Tiny support available varies from mobile to mobile, depending on the SVG engine installed. Many newer mobile products support additional features beyond SVG Tiny 1.1, like gradient and opacity; this is sometimes referred as "SVGT 1.1+", though there is no such standard.
Rim'sBlackBerry has built-in support for SVG Tiny 1.1 since version 5.0. Support continues for WebKit-based BlackBerry Torch browser in OS 6 and 7.
Nokia'sS60 platform has built-in support for SVG. For example, icons are generally rendered using the platform's SVG engine. Nokia has also led the JSR 226: Scalable 2D Vector Graphics API expert group that defines Java ME API for SVG presentation and manipulation. This API has been implemented in S60 Platform 3rd Edition Feature Pack 1 and onward. Some Series 40 phones also support SVG (such as Nokia 6280).
OpenVG is an API designed for hardware-accelerated 2D vector graphics. Its primary platforms are handheld devices, mobile phones, gaming or media consoles, and consumer electronic devices including operating systems with Gallium3D based graphics drivers.
Online SVG converters
This is an incomplete list of web applications that can convert SVG files to raster image formats (this process is known as rasterization), or raster images to SVG (this process is known as image tracing or vectorization) - without the need of installing a desktop software or browser plug-in.
Autotracer.org. Online raster image vectorizer using the AutoTrace library. BMP, GIF, JPEG, or PNG to DXF, EPS, PDF, or SVG. Upload limit: 1MB.
FileFormat.info  - Converts SVG to PNG, JPEG, TIFF. Output resolution can be specified. No batch processing. Upload limit: 5MB.
Online-Convert  - Converts to/from BMP, EPS, GIF, HDR, ICO, JPEG, PNG, SVG, TGA, TIFF, WBMP, WebP. No batch processing. The output (e. g. image size) is customizable; the conversion to SVG is handled by Potrace.
SVGConv  - Converts SVG to JPEG, PNG, GIF, BMP, TGA, TIFF, PDF, PS, EPS. Allows the user to customize the output (like image size, background color) and has batch processing features (converting multiple files in a single step). Upload limit: 10MB
SVG2Android  - Converts SVG to an Android VectorDrawable (introduced in API 21)
^"IRC log of svg on 2008-11-17". W3C. 2008. Retrieved 25 May 2009. DS: Priorities should be layout, diffusion curves, 2.5D and make sure we work well with CSS on that
^"Propositions for the next SVG spec". W3C. 16 March 2009. Retrieved 25 May 2009. Indeed, we do plan to add new gradient capabilities to SVG in the next version, and we are looking into diffusion curves, which I think will meet your needs ... *Diffusion curves* seems really a great idea.