A Tactile Web Browser for the Visually Disabled

Martin Rotard, Sven Knödler, Thomas Ertl Visualization and Interactive Systems Institute

University of Stuttgart Universitätsstrasse 38

70569 Stuttgart,Germany Phone: ++49-(0)711-7816-269

{rotard, ertl}@vis.uni-stuttgart.de, sven@vortexeu.com

ABSTRACT The dissemination of information available through the World Wide Web makes universal access more and more important and supports visually disabled people in their everyday life. In this paper we present a new approach for visually disabled people to browse and interact with web pages. Up to now graphical information is mostly ignored in transformations for visually disabled people. We propose a web browser, which uses a transformation schema to render web pages on a tactile graphics display. Bitmap images and Scalable Vector Graphics (SVG) can be explored in a special mode, in which filters can be applied and zooming is possible. Mathematical expressions encoded in the Mathematical Markup Language (MathML) are transformed into LaTeX or into a notation for visually disabled people. The web browser supports voice output to read text paragraphs and to provide feedback on interactions to the users.

Categories and Subject Descriptors H.5.4 [Information Interfaces and presentation] Hypertext/ Hypermedia –Architectures, Navigation, Theory, User issues K.4.2 [Computers and Society] Social Issues – Assistive technologies for persons with disabilities

General Terms Algorithms, Human Factors, Standardization, Theory

Keywords Tactile Graphics, Adaptive Hypertext, Multi-modal Interfaces, Universal Access

1. INTRODUCTION The World Wide Web allows visually disabled people to access information for their everyday life that is otherwise difficult to get. Examples are schedules of buses or trains, telephone numbers, the latest news, or learning materials in a virtual learning environment. To access this information visually disabled people use screen readers to extract the textual information, which is displayed on the screen. The extracted two-dimensional information is linearized and is either written in

Braille on a special output device or presented by voice output. However, graphical information is still ignored by screen readers or reduced to the file name of the image or to an alternative text if those exist at all.

Especially in scientific education it is necessary to have access to images, diagrams, and formulas. If this information is not accessible, the visually disabled students may not get a deep understanding of the relations in the learning materials. Particularly the missing of mathematical expressions and the related diagrams are a strong disadvantage.

Sometimes there are versions of web pages for visually disabled people, where the layout is reduced and the textual content is easier to access. Nevertheless visually disabled people want to browse on the same web pages, use the same links, and read the same content in the same layout like sighted people do. The special versions of web pages, if those exist at all, are an opportunity for visually disabled people to access the textual content, but they would rather prefer to access the entire content.

The next generation of web pages will use XML-based standards for illustrations and for mathematical expressions. In this context the World Wide Web Consortium (W3C) recommended the Scalable Vector Graphics (SVG) and the Mathematical Markup Language (MathML) [26, 25]. The advantages of vector graphics over raster graphics are that images can be enlarged or reduced without losing quality and the possibility to transform the images into another representation. The exploration of SVG on tactile graphical displays and the transformation of MathML expressions into a notation for visually disabled people were presented in our recent publications [20, 21]. Usually SVG images and MathML expressions are embedded in HTML (Hyper-Text Markup Language) or XHTML (Extensible HyperText Markup Language) documents.

In this article we propose a tactile web browser for HTML and XHTML documents that renders text and graphics for visually disabled people on a tactile graphics display and retains the two-dimensional structural information of the document. We implemented two exploration modes, one for bitmap graphics and the other for Scalable Vector Graphics. The second mode is based on our transformation schema presented in [21].

For our experiments, we use a Metec pin matrix device. This tactile graphics display has a display area of 37x19 cm and 120x60 pins, which are set electromagnetically. Figure 1 shows the device displaying an image. Our solution is not restricted to the size of the graphics display that we use and can be configured

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for other devices and resolutions. The approach in transforming mathematical expressions in MathML into a special notation for visually disabled people is also not restricted. The output notation can be changed easily by adding another XSLT-stylesheet (Extensible Stylesheet Transformations).

The remainder of this paper is structured as follows. Section 2 discusses related work. In section 3 we present the transformation schema for tactile web pages. In this section we describe how we handle styles, layout, colors, images, tables, lists, and frames to meet the requirements on tactile devices. Section 4 explains how graphical information can be explored by visually disabled people. Section 5 presents the exploration methods in our system for bitmap graphics, Scalable Vector Graphics and mathematical expressions in MathML. Section 6 describes the architecture and tools that we use in our implementation. Section 7 presents our preliminary usability results and section 8 draws conclusions and discusses future work.

2. RELATED WORK The phrase "surfing the web" implies rapid and free movement and represents the travel and movement of sighted and visually disabled people on web pages. The browsing of web pages in detail is multifaceted [8, 18]. Recent survey studies support that especially for visually disabled people navigation in complex web pages is complicated [6, 9]. The reason for this is the non-linearity of tables and frames. For visually impaired people these two-dimensional constructs are linearized. This leads to a substantial loss of semantic content [19].

Two-dimensional structural information of simple hypertext and interactive videotex service were presented by Kochanek and by Schweikhardt before the appearance of the web [12, 23]. Other approaches show just a small but scalable and scrollable part of the entire graphical user interface for sighted users on a tactile graphics display [10]. The transformation of mathematical expressions in MathML into a notation for visually disabled people using XSLT is possible for many notations [11].

Special browsers or screen readers read out the content of web pages word by word and only some of them can support the navigation in tables [1, 5, 7, 29]. Recent developments make use of conceptual structures (automatically or manually derived) for navigation on web pages, where the document structures are stored as conceptual graphs [13, 19].

The results of our transformation schema for web pages into a tactile representation is best when the HTML source code is valid and semantically correct regarding the standards of the W3C. The Web Accessibility Initiative (WAI) of the W3C has recommended a Web Content Accessibility Guideline [4]. This and other guidelines assist the authors in writing their web pages in an accessible way [16].

Due to the techniques for rendering HTML on tactile graphics displays with small resolution, related topics are displaying HTML documents on small hand held devices such as personal digital assistants (PDAs), or cellular phones. For these devices special browsers linearize the two-dimensional structural information or present a multi level summarization of the hierarchical structure [2, 17].

3. TRANSFORMATION SCHEMA FOR TACTILE WEB PAGES Our transformation schema can process HTML and XHTML documents. Because XML-parsers (Extensible Markup Language) can exclusively process well formed XML-based documents, the HTML documents have to be converted into XHTML. After the XML-parser step the XHTML-tags and attributes have to be assigned to internal rendering classes. Depending on this categorization the content of the tags and attributes is extracted and stored in an internal tree structure.

3.1 Style and Layout HTML-documents are styled by a set of Cascading Style Sheets (CSS). The CSS-attributes can be found in an external file, in the <style>-tag of the HTML-document or inline in the style-attribute

Figure 1: Tactile graphics display with a resolution of 120x60 pins displaying an image

of an HTML-tag. To extract this information we developed a simple CSS-parser.

The layout of HTML-documents is achieved by headings, text paragraphs, tables, lists, images, etc. In our transformation schema we have to calculate the layout for the reduced resolution of the tactile graphics display. The tactile layout must not exceed the graphics display's boundaries, because horizontal scrolling is an additional cognitive effort. Therefore, we calculate boxes for each element like text paragraphs or images. HTML text can flow around an image which results in non-rectangular rendering areas for text paragraphs. Thus, we split these areas into a number of rectangular rendering areas. For a single image, which has a text paragraph flowing around its right edge, this method would create two boxes for the text paragraphs, one to the right of the image and another one below (see figure 2).

Text is rendered on the tactile graphics display in 8-dot Braille. Because Braille characters have a fixed width and height, zooming of textual information is impossible. Text attributes are written directly as special style tags into the text. For these special style tags abbreviations are used to keep the insertion as short as possible. Bold face is designated as "<b>", italic as "<i>", underlined as "<u>", links as "<a>", colors as "<c=color>", heading 1 to 6 as "<h1>" to "<h6>" etc. The text attributes are output in a compact notation to use as few textual characters as

possible, e.g. a textual content that is written in bold face and in green color, has the text attributes <b c=green> as prefix.

The title of the web page is an important information for visually disabled people. Therefore the title is written in the first line of the tactile output.

3.2 Colors Color is important for visually disabled people, because it is an attribute that is used to distinguish objects and to group properties in illustrations. In HTML and CSS color attributes can be set by using color keyword names or by hexadecimal values in the syntax "#RRGGBB"(R=red, G=green, B=blue). Especially the hexadecimal values are not feasible for visually disabled people. Hexadecimal color attributes can be used as metadata information, when they are converted into color keyword names or into distinguishable user defined color names. Therefore, we implemented a transformation, which converts this hexadecimal value into the nearest color keyword name. For the conversion we transform the RGB-value into the L*a*b color space, because in this color space distances can be measured exactly for the human color recognition [15]. In this approach the color keyword names can be configured depending on the distinguishable colors by the user.

3.3 Scaling of Images Because of the small resolution of tactile graphics displays, the images that are embedded in the text of the document have to be scaled down. The resolution of our tactile graphics displays is 120 to 60 pins. It is important to retain the ratio between the size of the image and the size of the standard user screen (we suppose 1024 pixels), because the size of an image is a serious parameter for the impression and orientation of the user. In our first approach we tried to keep this ratio constant. But we noticed that this linear function scales down small images so dramatically, that they are not useful anymore. However, small images can be important, since they are often used as symbols in the navigation or in graphical menus. Therefore, in a second approach we decided to take the square root of the ratio. Using the square root, small images are scaled down with a lower factor, than larger images. The size of the images can be changed by adding a linear factor, which could be increased or decreased interactively by the user.

Figure 2: Layout boxes for a single image and a text paragraph that flows around the image

Figure 3: A web page with mathematical content, which includes text paragraphs and bitmap images

Figure 4: The web page rendered by our tactile web browser for a tactile graphics display (simulation on the left and

magnified area on the right)

The transformation of images and formulas will be described in detail in section 5.

3.4 Tables, Lists, and Frames In HTML tables are used for the layout of web pages and for structured output of information. In our transformation schema, we generate output that fits the size of the tactile graphics display. Therefore, the border of tables is reduced to a width of only one single pixel and the margin and spacing of table cells is optimized for space reduction. Each list element is rendered in a single line by transforming the list's textual information to its representing Braille character string. The bullets of unnumbered lists are rendered into a special character, with all eight dots set. In order to deal with the complexity of frame sets, frames are presented in a list, where the user can select a frame and explore it. In this way we can achieve both, simplification of navigation and a compact presentation of frame sets that otherwise would result in large areas that exceed the graphics display's boundaries and thus could only be explored with high navigational and cognitive effort.

3.5 Example Transformation As an example figure 3 shows mathematical content in a web page. The result of the transformation on the tactile graphics display is shown in figure 4. In this document, the text is encoded in Braille, the style information of the headline is embedded into the text, and the diagram is encoded as a tactile image. Figure 5 shows the diagram in the bitmap graphics exploration mode. Figure 6 shows an excerpt of a typically web page. On the upper part is an address block and a photo. On the bottom of the excerpt there is a table. The tactile output of the transformation schema contains two screens that are shown in figure 7 and 8. The size of the photo is increased to make the exploration easier for the visually disabled user.

4. INTERACTION TECHNIQUES The basic idea of hypertext is to have links to related documents. In the tactile HTML browser there is a method to select links and images by pressing a special key. The selection starts at the

content, which is actually on the tactile graphics display. This is very important, because it prevents the user from loosing the context, which is similar to the lost in hyperspace phenomena described 1997 by Conklin [3]. The user can cycle through the links and images. The selected item is highlighted by blinking on the tactile output device. After a link or image is selected, it can be activated. In the case of a link, the related document will be displayed and in the case of an image the exploration mode will be activated. In this mode the image is displayed in the maximum size of the tactile graphics display and can be zoomed. Additionally, filters can be applied on the image, which make it possible to handle more complicated visual information. The text of the document can be read to the user by a text-to-speech engine, starting at the current position on the tactile graphics display. Voice output is also used to give feedback about the current modes, the link names, and the alternative tags of images.

5. TACTILE IMAGES Since tactile graphics displays can only represent two states per pin (pin up or down), images have to be reduced to monochrome colors. Therefore, it is necessary to separate fore- and background. HTML-documents can have different kinds of graphical information. Bitmap graphics in web pages are commonly used for photos, illustrations and formulas. The next generation of web pages will use Scalable Vector Graphics for illustrations and MathML expressions [26, 25]. These recommendations of the W3C provide great advantages in accessibility. The main advantage of both graphical standards is that they are based on XML. Therefore, their components are structured in separated objects which can be transformed into another representation by using XSLT. Scalable Vector Graphics can be used in diagrams, business charts, maps, etc. The image can be generated by a script, e.g. the semantic information of an UML (Unified Modeling Language) diagram encoded in a markup language for UML, like XMI (XML Metadata Interchange), can be rendered in a standardized UML diagram.

Figure 5: A diagram in the bitmap graphics exploration mode (simulation on the left, magnified area on the right)

Figure 6: Web page example including text and photo and table at the bottom

5.1 Bitmap Graphics In order to reduce true color bitmap graphics into a semantically adequate monochrome representation, image understanding or computer vision methods are necessary. However, specialized algorithms often only work in dedicated contexts or do not perform in real-time. We have had reasonable success using threshold based methods. To identify the background in an image, we calculate a range depending on the threshold in the histogram with the maximum occurrence. These values are mapped to pins down on the tactile graphical display. The other values are mapped to pins up. During exploration the user can adapt the threshold interactively.

Another approach maps high luminance values to pins down and low values to pins up on the tactile graphical display. The threshold value can also be adapted interactively by the user during exploration. This approach works well on diagrams or formulas that are in black and white. On colored backgrounds the first approach is more flexible. Results of transformations using this method are shown in the full screen exploration mode in Figure 5 and included in the web page in figure 7. For visually disabled people edges are very important in the exploration of images. Therefore we added a sobel edge detection filter.

Figure 7: First tactile page including text and photo (simulation on the left and magnified area on the right)

Figure 8: Second tactile page including the table (simulation on the left and magnified area on the right)

5.2 Scalable Vector Graphics Scalable Vector Graphics (SVG) is a language for describing two-dimensional graphics in XML. It was recommended by the W3C in 2001 [26]. Figure 9 shows an example image of a mathematical diagram in SVG. In a recent publication we presented the rendering of SVG on the tactile graphics display (figure 10). The SVG exploration mode is based on this toolkit. The transformation of SVG into an accessible form can be very flexible, because the entire groups, shapes, attributes and the content of text elements are encoded in XML and can be extracted separately. This makes it possible to build up the image incrementally shape-by-shape [21]. Therefore, the shapes are sorted spatially from left to right and from top to bottom. Figure 11 shows one step of the incrementally buildup. The example

image is grouped semantically into several parts like axes, function, etc. The exploration of images is easier when filters can be applied on demand. One of the filters removes gradients and patterns in fillings. A contour filter removes the fillings of shapes and shows just the edges. Furthermore color filters can be used to show just shapes of a specific set of colors. A text filter allows to navigate sequentially to text elements and shows the position of the text by blinking. The text content is output on the Braille line and by voice output. In figure 10 and 11 text is not encoded in Braille, because Braille characters have a fixed width and height, which could lead to an overlap with the graphical information. To avoid unreadable text, a possibility would be to render each text element on a rectangle, which has the color of the background. In every interaction step the user is informed about title, descriptions, and attributes like shape type, color, content of the text shapes by voice output.

5.3 Mathematical Expressions Mathematical Markup Language (MathML) is a language for describing mathematics in XML. The source code of mathematical expressions in MathML is in principle legible for visual disabled people due to its linear textual notation. However, it is not comfortable for this purpose because of its verbosity and complexity. This makes a transformation of MathML expressions into a compact mathematical notation, which is legible for visually disabled people, necessary. We integrated in our tactile browser the transformations of MathML expressions into LaTeX and into the Stuttgart Mathematical Notation For the Blind (SMFB) [20]. The transformation into SMFB was recently published by us [22]. SMFB is a mathematical notation for visually disabled people that has been developed at the University of Stuttgart since 1980 and is encoded in 8-dot Braille. The transformation is based on an XSLT-stylesheet. The results are embedded directly into the web page replacing the previous MathML expression. The transformation of MathML expressions into LaTeX and the integration into the web page is done by using a XSLT-stylesheet, too [28].

6. ARCHITECTURE AND TOOLS The tactile web browser is implemented in Java. Documents that are not conforming to the W3C-standard have to be corrected by using heuristic methods. The correction and conversion of HTML into XHTML is accomplished by JTidy [24], which is a Java port of HTML Tidy of the W3C. Java classes are used to transform the XHTML structure into a tactile representation. Some transformations are much easier to accomplish in XSLT-stylesheets. Therefore we integrate XSLT in the processing. The XSLT-stylesheets are processed using Xalan [27]. For the voice output feedback we integrated FreeTTS as text-to-speech engine [14].

7. PRELIMINARY USER TEST RESULTS The tactile web browser was tested by visually disabled people. This led to some preliminary usability results. Although the two-dimensional layout was unfamiliar for visually disabled people, it turned out to be very useful. The handling of selecting links and images was intuitive and easy. Especially the exploration of tactile graphics including zooming, scrolling and applying filters

Figure 9: A diagram, which is encoded as Scalable Vector Graphics

Figure 10: The diagram in the vector graphics exploration mode (simulation on the left and magnified area on the right)

Figure 11: An incremental buildup step, in which the axes of the diagram are shown first and the values of the function are

displayed in a second step (simulation on the left and magnified area on the right)

was new to the users. A short training in exploring tactile images increased their ability rapidly. Nevertheless, exploring tactile images is difficult and users could not figure out what some of the images depicted. Figure 12 shows a photo of the mathematical diagram in figure 9 in the graphics exploration mode on the tactile graphics display. The exploration of Scalable Vector Graphics was appreciated as more flexible compared to bitmap graphics. The incremental buildup and the color filters helped the users to identify the objects in the images and to grasp their semantic meaning.

8. CONCLUSION AND OUTLOOK We proposed a transformation schema, which opens a new way for browsing of web pages for visually disabled people. We implemented a web browser to render web pages on tactile graphics display. The tactile web browser helps visually disabled people to get access to the World Wide Web in a two-dimensional rather than linearized representation. Bitmap and Scalable Vector Graphics can be explored in a special mode. Mathematical expressions are transformed into a notation for visually disabled people. The preliminary user test results are very promising and show that the two-dimensional structure and the exploration of graphical information is an advantage for visually disabled people in grasping the semantic meaning of web pages and learning materials. Optical Character Recognition (OCR) and useful filters for image segmentation, color quantization, etc. are functionalities to be integrated for bitmap graphics in the next version of our tactile web browser. The proposed transformation schema is not complete and could also be optimized. Some HTML tags like forms and active scripting components and plugins for Java and Flash are still missing and will be realized in a future version. The integration of new standards like XForms would be helpful. One approach to work on these challenges would be to integrate our transformation schema into a browser like Firefox or Mozilla.

9. ACKNOWLEDGMENTS We would like to thank Alfred Werner, Joachim Diepstraten, Kerstin Otte, and Gerhard Weber for their help to finish this paper and for the fruitful discussions

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