Highly Accessible Scientific Graphical Information through DAISY SVG

Improving SVG for Perfect Accessibility

John Gardner

John Gardner is Professor Emeritus of Physics, Oregon State University and president of ViewPlus Technologies. He lost his sight in 1988 and founded ViewPlus to develop and market technologies for better information access by people with print disabilities.

Vladimir Bulatov

Vladimir Bulatov is a theoretical physicist who began working on graphical information accessibility as a Postdoctoral Associate at Oregon State University and is now senior scientist at ViewPlus. He is the principal author of the IVEO technology.


SVG includes features that help to make SVG graphical information accessible to people who are blind or dyslexic. ViewPlus’ IVEO technology provides SVG authoring and viewing applications that make this promise a reality. ViewPlus is now collaborating with the DAISY (Digitally Accessible Information SYstem) consortium to develop author guidelines and to expand SVG to provide features making DAISY SVG excellent both for making current graphical information accessible and for making future mainstream information more useful and more fully accessible.

Table of Contents

1. Introduction
2. The IVEO Audio-Touch Technology
3. Practical Problems Affecting SVG Accessibility
4. The DAISY Approach
5. DAISY Elements and Attributes
5.1. Layers
5.3. Actions
5.4. Overlays
5.5. Text Structure

1. Introduction

SVG 1.0 and 2.0 include two features, title and description properties for graphical objects, intended to promote accessibility of SVG to people with print disabilities. ViewPlus has exploited these two fields in its IVEO technology to permit SVG images to be accessible to blind and dyslexic readers [1], [2]

The ViewPlus IVEO Viewer is used along with a tactile copy of the image to allow Audio-Touch [3], [4] access to graphical information. The blind reader typically has a tactile copy (made by printing the SVG page from IVEO Viewer to a ViewPlus embosser) mounted on a touchpad When text or a graphical object is tapped, it is selected and the text span or object title respectively is spoken by the computer. An object description is spoken when the user presses a computer hot key or double taps the object. The IVEO Audio-touch method provides excellent access by people with print disabilities if the SVG objects and text spans are organized into semantically-meaningful structures and important graphical objects provided with semantically-meaningful titles and descriptions.

2. The IVEO Audio-Touch Technology

IVEO Creator is a WYSIWYG SVG authoring application that can be used to create simple SVG images and add labels to the graphical objects. It has limited authoring capability. It is intended primarily to import SVG and add titles and descriptions to the SVG file and to important graphical objects in the image. It can also add other features such as human-recorded information. Human speech is more understandable than what is normally provided by speech engines.

IVEO Creator Pro extends those capabilities by permitting files in any electronic image formats to be imported and converted to SVG. In general, vector graphic structure is preserved, and text converted from its original format to SVG format. Bit map images can also be imported. OCR (Optical Character Recognition) of bit map images interprets bit map text and overlays it with text in SVG format. However there are no graphical objects in bit map images, and OCR conversion errors can affect text. In principle, vector files provide not only better visual images but much better access to people with print disabilities. This promise is seldom realized in practice however.

3. Practical Problems Affecting SVG Accessibility

Unfortunately, most common graphical authoring applications do not export well-structured SVG. The lowest level graphical objects are often semantically meaningful but are seldom organized into any meaningful structure. Text is seldom organized into semantically-meaningful spans. Many graphics authoring applications produce SVG and other format files with text words broken into several spans or with text expressed in local font tables that are often difficult to convert to unicode. When such text spans are spoken by a speech engine, the output is difficult or impossible to understand.

Many practical difficulties affect text in scientific diagrams. Scientific graph authoring applications often put several semantically different text strings into a single span. X axis labels for example are often in a single span. Touching any x axis label causes all labels to be read aloud. Scientific graphics frequently have labels with Greek and other scientific characters. They often have sub- and super-scripts and occasionally relatively complex mathematical, chemical, or other specialized expressions. SVG does not anticipate complex expressions, and it is not possible to express many math equations in a single semantically-meaningful SVG text span. Even when SVG structures are available for such expressions, authoring applications do not export the equation in that structure. Greek characters, bold or other emphasized characters are often placed in text spans separate from that of the full expression. Commonly all bold characters in an image may be contained in the same text span even though they may belong to entirely separate scientific expressions. These authoring conventions can produce good visual text but be semantic nonsense.

4. The DAISY Approach

The DAISY (Digital Accessible Information SYstem http://www.daisy.org) consortium has taken a leadership role in trying to overcome the practical difficulties discussed above. DAISY is an international consortium of libraries and other agencies serving needs of the blind and dyslexic. The DAISY logo is widely recognized as the international information accessibility brand. The DAISY XML specification is widely used by agencies around the globe to make information accessible to people with print disabilities. It is being integrated with the epub electronic book format and is increasingly being recognized as an excellent mainstream electronic publication format.

DAISY has formed an SVG Working Group to develop authring guidelines and to expand SVG to provide a good format for excellent accessibility to graphical information. Several ViewPlus developers are leaders of that DAISY group, and IVEO is the vehicle for testing and implementing DAISY SVG. This work is still in progress, so this paper may be considered an interim report on progress.

5. DAISY Elements and Attributes

The DAISY SVG Working Group is presently testing a number of optional additional structures and attributes. Some of these are intended for use by agencies and publishers making materials designed for people with print disabilities. Many have solid mainstream uses as well.

DAISY layers are structural elements permitting text and graphical objects to be grouped to have a broad set of useful properties

The set of DAISY layers are defined by a sequence of form

     <daisy:layerItem layer_attributes /> 
     <daisy:layerItem layer_attributes /> 

The layer_attributes control properties of graphical elements assigned to that layer. <layerItem> may have the following attributes:

  • id = "layer ID" - id of layer to be used to refer to the layer in graphical elements.
  • name = "layer name", name displayed to user in layers list.
  • display = "on" or "off" specifies whether layer elements are displayed on screen.
  • print = "on" or "off" specifies whether layer elements will be printed on visual media.
  • emboss = "on" or "off" specifies whether layer elements will be embossed, a feature permitting taktile output to be different from visual output.
  • active = "on" or "off" specifies whether layer elements are active in user interaction (eg spoken when selected)
  • lock = "on" or "off" specifies whether layer elements are locked to prevent selection and editing.
  • enabledInViewer = "on" or "off" - specifies whether the layer should be completely disabled or enabled in viewer, allows a designer (eg teacher) to customize one master graphical document for different needs/users.

Any SVG visual element may be assigned to a layer by giving it the attribute daisy:layer = "layerID".

A DAISY View permits one document to show many different portions of the image (eg a full map of the US as well as a view of northeastern states and a view of Washington DC).

The set of views is defined by the element , having an arbitrary number of children, .

Each viewItem has the following attributes:

  • name="view name", the name displayed in the user view list
  • x="x-coordinate of view"
  • y="y-coordinate of view"
  • width="width of view"
  • height="height of view"

x, y, width and height attributes are given relative to viewBox. Default view for example, equivalent to the full svg viewBox, is x = "0." y = "0." width="1." height="1.".

DAISY text structure is still under active development. It will permit SVG text to be structured into semantically meaningful columns, sentences, and words. It has a number of purposes.
  • For bit map images, the text can be incorporated fully into the DAISY structure so that SVG text overlay (which often detracts visually from the image) will no longer be necessary. The structure will include the bounding rectangles of words so that they may be highlighted when selected and read. This method may also be used to speak semantically-meaningful information when true SVG text is present but is not organized into semantically-meaningful spans. This use is intended for "making information accessible" and is not recommended for authoring applications.
  • For charts and diagrams with large amounts of text, related text (eg paragraph inside a box) can be spoken in semantically meaningful spans, browsed, etc.
  • Math expressions can be associated with the MathML equivalent, permitting an equation to be spoken in a semantically meaningful manner. Without this additional infformation, an equation is just a collection of symbols not easily interpreted by audio/touch.

The DAISY text structure specifications are being developed as a joint project of DAISY, ViewPlus, and the Infty group http://www.inftyproject.org. The Infty group has developed math OCR capability and is working to modify its Infty reader math OCR application to recognize text and math in SVG files. It then organizes them into the appropriate DAISY text structures. This capability will be licensed to ViewPlus for its IVEO Creator Pro application.