Sheets (CSS), handling of dynamic web content controlled by JavaScript code, etc. ..... tries to convert HTML pages into XHTML with the help of JTidy [14] before.
Tactile Web Browsing for Blind People Martin Rotard, Christiane Taras, and Thomas Ertl Visualization and Interactive Systems Institute Universit¨ at Stuttgart Universit¨ atsstraße 38 70569 Stuttgart, Germany Phone: +49-(0)711-7816-269 {rotard, taras, ertl}@vis.uni-stuttgart.de
Abstract. Information on the World Wide Web becomes more and more important for our society. For blind people this is a chance to access more information for their everyday life. In this paper we propose novel methods to present web pages including graphical information on a tactile output device. We present a Mozilla Firefox Extension for the tactile rendering of web pages and for the handling of user interactions. This approach benefits from the Firefox built-in web page handling including parsing of HTML documents, formatting with Cascading Style Sheets (CSS), handling of dynamic web content controlled by JavaScript code, etc. Graphical information can be explored and filtered interactively in a special mode for raster images and Scalable Vector Graphics (SVG). Mathematical expressions encoded in the Mathematical Markup Language (MathML) are transformed directly into LaTeX or into a notation for blind people. The tactile web browser supports feedback that is provided via voice output.
Key words: Accessibility, Haptics, Tactile Graphics, Web Browsers
1
Motivation
The development of the World Wide Web is a great benefit not only for sighted people but also for blind people. The web enables blind people to access information much easier than by printed media for example. Potentially the web gives blind people the possibility to access the same information like sighted people do. In e-learning courses for example blind people may even take part in ordinary programs of study. Unfortunately there are some problems blind people have to face with when browsing the web. Since web pages get more and more complex, information is not only presented in simple text but also as graphical information and layout. Especially in scientific education it is necessary to have access to images, diagrams, and formulas. If these parts are not accessible, blind students may not get a deep understanding of the relations in the learning material. Currently blind people mainly use screen readers to access web pages. Screen readers extract the textual information and linearize it for the output on Braille
displays or for voice output. So any kind of graphical information is inaccessible. Furthermore text is only presented line by line on the Braille display or auditory. This makes it even harder to get an overview of the web page, to understand the relations of its different parts, and to identify the navigation links. To address this problem a tactile graphics display was developed together with Metec [22] in the middle of the eighties. Using this device it is possible to present graphics and multi-line text to blind people. Thus with our tactile browser the exploration of information on the web becomes much easier and holistic for blind people. In the following sections we summarize our recent work related to the tactile graphics display and present new ideas and concepts for future work. Parts of the described results have already been discussed in detail in referred publications [27, 31, 28, 30, 29].
2
Related Work
Browsing the web today is different than it was ten years ago. Usually today’s web pages are complex structures that consist of dozens of tables, lists, links, frames, textual, and graphical information. The browsing of web pages in detail is multifaceted [11, 25]. Recent survey studies support that especially for blind people navigation in complex web pages is complicated [8, 12]. The reason for this is the non-linearity of tables and frames. For blind people these two-dimensional constructs are linearized. This leads to a substantial loss of semantic content [26]. Before the appearance of the web Dirk Kochanek and Waltraud Schweikhardt presented two-dimensional structural information of simple hypertext and interactive videotex service [17, 33]. Furthermore there are special browsers or screen readers that can read out the content of web pages word by word but only some of them have advanced support for table navigation [1, 6, 10, 36]. 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 [18, 26]. A great benefit for special browsers and screen readers brought the Web Content Accessibility Guidelines [4] which was published by the Web Accessibility Initiative (WAI) of the World Wide Web Consortium. These Guidelines recommend writing valid and semantically correct HTML source code regarding the standards of the W3C to get the best accessibility results. For example the use of MathML to mark up mathematical expressions is recommended by this guideline. Therefor Karshmer et al. showed that the transformation of mathematical expressions in MathML into a notation for blind people using XSLT is possible for many notations [15]. One such notation is the Lambda notation which was developed to enable linear access to mathematics for Braille devices and audio synthesis [9]. Considering the tactile graphics display presented in this paper other tactile matrix devices are to be mentioned. Handytech, for example, developed a small
tactile device that handles a small but scalable and scrollable part of entire graphical user interfaces [13]. For the rendering on tactile graphics displays algorithms are used that are similar to the algorithms used in browsers for small mobile devices like personal digital assistants (PDAs) or cellular phones which provide small screen rendering for web pages. The methods that are used for this kind of rendering are linearization of the two-dimensional structural information or presentation of multi level summarization of the hierarchical structure [24, 3]. Even more complex than presenting 2D information to blind people is the presentation of 3D information. Therefor Yoshihiro Kawai and Fumiaki Tomita have presented an interactive tactile display system that is able to support blind people in recognizing 3D objects [16]. Furthermore Martin Kurze has done some work in the recognition of three-dimensional objects by blind people [19, 20]. An overview on methods in tactile 3D graphics is given by Kevin Christian [5].
3
Tactile Graphics Displays
Tactile graphics displays give blind people great benefits. They are a kind of multi-line Braille lines so it is possible to present multiple lines of text and even graphics on them. The basic concepts used for tactile displays are the same as used for Braille lines. They are built with a number of pins which can be lifted or lowered. Considering text pins are lifted to show the dots of Braille characters. The interactive tactile displays also have advantages over conventional methods in presenting graphics. By using embossers for example it is only possible to produce static representations. Each new graphic needs a new sheet of paper and after embossing the graphic cannot be reset anymore. On tactile displays graphics may be presented dynamically so that the user may even interact with the graphics, e.g. by zooming in and out or applying filters. A difference between Braille lines and tactile graphics displays is that the pins on tactile displays are not grouped somehow. All pins have the same displacement to their neighbors so that no gaps emerge when displaying graphics. The spaces that are needed when displaying text have to be generated deliberately by leaving single lines and rows of pins lowered between different characters. For graphical presentations it is a strong restriction that only two pin states exist. Therefore every graphic has to be converted to a monochrome representation. In section 5 algorithms to handle this convertion are discussed. Tactile graphics displays exist in different resolutions. There are really small displays, like the GWP from Handytech [13], which can be used to show small graphics, e.g. icons, in detail. The display we are using has a resolution of 120x60 pins (see figure 1). Of course compared to modern computer monitors this resolution is quiet low but in fact it is feasible for our needs. On the display text of 40 characters width and 12 lines height can be presented at a time when using 8-dot Braille. Our display, called ”Stuttgarter Stiftplatte”, was developed in collaboration with Metec [22]. It is build on electromagnetic technology which means that
Fig. 1. Photography of the Metec display
the pins are lifted with the help of elastic springs, inductors, iron cores and little metal bars connected to the pins. If the iron core related to a pin is not magnetized the pin is pushed out of the displays’ surface by the spring. If the iron core gets magnetized by a direct current stimulus to the inductor the metal bar at the bottom of the pin is dragged on the iron core and so the pin is lowered [34]. Figure 2 illustrates this. The magnetized iron core acts as a permanent magnet. If a lifted pin is pressed down by the user it raises again when the users’ fingers move on.
Fig. 2. Schematic representation of the functionality of the Metec display [34]
A great benefit for our display was the extension of two input devices. By using these input devices direct manipulation of text and graphics presented on the display is possible. So for example text sections may be marked or hyperlinks may be activated through by interactions directly on the display. The input devices also operate electromagnetically [34].
Unfortunately the existing display has some major problems. At first it is approximately as big as an ordinary PC desktop and its weight is about 20 kilos. Furthermore there is an external control unit connected to the display. So the display is not really portable. Besides the existing display is quiet slow. The change of all pins on the display takes about 30 seconds, this can be speed up using special algorithms which send not the whole matrix states but only the necessary differences. Therefore at the moment we are planning to develop a new tactile display. The aim is to design a touch sensitive display which is much more portable and allows direct manipulation without special input devices. Unlike the old display the new one will be based on piezo technology. This will make the display much faster in lifting and lowering the pins. So for example scrolling may be much faster than it was on the old display.
4
A Tactile Browser
To give blind people the chance to navigate through the World Wide Web like sighted people do we are developing a tactile browser that renders web pages on the tactile graphics display described in section 3. In the first approach we have implemented a browser in Java that is independent from other web browsers. Thereby we developed many useful concepts relating to tactile web navigation. As this browser has some disadvantages we decided to implement a new tactile browser based on an ordinary, existing web browser. This gives us the possibility to directly use many features of the existing browser. So we can concentrate on our own features. 4.1
First Approach
In the first approach we have implemented an independent browser which uses its own parsing and rendering methods to handle web pages [30]. This browser is able to render XHTML documents in Braille on the tactile display. A main requirement for the tactile browser was to render web pages in such a way that no horizontal scrolling is needed as this is rather confusing for users. Nevertheless the two dimensional structural information of the original document should be retained as far as possible. We implemented a layout algorithm that uses a box model to solve this problem. The algorithm is inspired by the ones used for hand held devices [24]. Figures 3 and 4 show the German Google web page (http://www.google.de) like it is presented in an ordinary browser and rendered by the tactile browser respectively. The continuous border in figure 3 marks the part of the web page which is shown on the first page of the tactile version (figure 4). The lower part of the web page, marked with the dashed border, would be shown on a second page on the tactile display. To be able to present all style information of the web page elements to the user the browser furthermore parses the Cascading Style Sheets (CSS) related to the web page. For every element of the page all style information is collected recursively in the DOM tree. The browser is able to present text style information
Fig. 3. German web page of Google (http://www.google.de) in an ordinary browser (part with continuous border is shown in figure 4, part with dashed border would be shown on a second page on the tactile display).
Fig. 4. Upper part of the German web page of Google (http://www.google.de) rendered by the tactile browser (form fields are not displayed)
in the Braille text and to provide it via voice output so that this information is accessible to the users. One great benefit of the tactile browser is the ability to render graphics. Therefor different algorithms were implemented to reduce the resolution to fit the dimensions of the tactile display and to convert to monochrome colors. All graphics can be explored in a special graphics exploration mode of the browser. In this mode more details may be presented. Furthermore the user may influence the presentation of the graphics via different filters (see section 5).
Another benefit of this browser is the implemented handling of tables. Because of the requirement to avoid horizontal scrolling tables in web pages have to be handled in a special way. Tables consist of rows and columns which may contain texts, graphics or even other tables. So they cannot simply be scaled down until the table width fits the tactile display as the cell content cannot be downsized arbitrarily. Braille characters for example need a certain space on the tactile display and graphics are not recognizable if they are too small. To avoid horizontal scrolling and nevertheless obtain the right sizes for texts and graphics one could simply linearize tables as often done on mobile devices for example [24]. This however raises the problem that information is lost if the table contains real two-dimensional data, e.g. calculation tables. So we decided to implement an algorithm which tries to preserve as much of the two-dimensional structure as possible and nevertheless presents texts and graphics in an appropriate size. The algorithm mainly works with the rows of tables. Considering a minimal size of text cells and the necessary size of graphics the algorithm linearizes tables row by row. This means it appends the cells of one row consecutively as long as the width of the tactile display is not exceeded. If the row contains further cells these cells are rendered on the next row of the tactile display. The algorithm differs from normal linearization as it definitely begins a new row on the tactile display for each row of the original table. So the original structure stays comprehensible. Figure 5 shows a table with four columns and two rows in its original structure, in linearized structure and like its rendered by the tactile browser.
Fig. 5. original structure of a table (left), the same table linearized (middle), the same table as rendered by the tactile browser (right)
All in all this tactile browser implementation has a lot of benefits for blind people navigating the World Wide Web. Many useful concepts for handling web pages on a tactile display were developed and implemented. But unfortunately this implementation has a problem rendering arbitrary web pages. The used XML-parser can only process well formed XML-based documents. So the browser tries to convert HTML pages into XHTML with the help of JTidy [14] before parsing them. Regrettably several web pages cannot be converted to well-formed XML by JTidy and so our browser is not able to not display them. Furthermore
dynamic content like navigation bars in JavaScript are not easy to handle. Finally form fields are not supported by the browser at all. To solve these problems we have decided to reimplement our tactile browser using an existing browser as basis. 4.2
New Approach based on Firefox
Using an existing browser as basis for our tactile web browser has the advantage that the user may benefit from the functionalities of the existing browser. For example we do not need to care about creating the DOM tree of web pages and the handling of dynamic content or Cascading Style Sheets (CSS). We can assume that the developers of the ordinary browser will keep its parsing routines up-to-date so that they will be able to parse existing web pages. Furthermore features like the management of sessions and cookies are already implemented in these browsers. We decided to use Firefox as underlying browser since this web browser is available for different platforms and furthermore it can be easily extended. During the last years Firefox got more and more users. Today even in companies using Microsoft Windows as operating system Firefox is often installed on the employees’ PCs by default. So building up on Firefox is not really constraining the usability of our tactile browser. As already mentioned a main benefit of using an existing browser is that we can use its parsing routines. Beyond this we want to benefit from the layout algorithms of the underlying browser. In Firefox this is possible by using the nsIAccessible interfaces [23] to determine the absolute screen positions of most elements of a web page. Taking this as basis we implemented a prototypic Firefox extension that applies a special Cascading Style Sheet (CSS) to the current web page, computes the relative positions of visible parts to their positions in the tactile representation and finally presents the visible parts on the tactile display. Before applying the style sheet some modifications of the web page’s source code are necessary. For example tables in web pages must be analyzed to determine how to represent them on the tactile display the best way. One possibility is to just linearize them, but this is not always the best solution as tables are used to present real two-dimensional information should not be linearized. Another possibility is to treat them as described for the first approach of our browser. But this does not seem to be the best solution for big tables and for tables that are just used for layout. Maybe this decision should depend from the information inside the table. Therefore we are working on a heuristic method to identify layout structures. An extended solution would be to integrate a special exploration mode for tables. Also difficult to handle are form fields like combo boxes. Here the question is if it is better to show the whole content of these fields directly on the web page or just one item as it is displayed for sighted users. The first solution has the advantage that no further interaction is needed to see all items but there is the risk to waste much space for a long list of words which does not interest the user. The second solution desires a special marking of such fields to give the user a
hint that there is a box that may be opened by clicking on it to see more items. At the moment we are developing concepts to solve such problems related to form fields. The aim is to support even complex web forms so that blind people can use search engines, access web shops or contribute their knowledge to wikis. After the modification steps the style sheet is applied to the web page. This style sheet mainly forces a certain ratio of the web page’s viewport width and the used font size. Furthermore images, icons and diagrams are scaled and some other formats are applied considering tables, links, lists and form fields. After that the currently visible parts of the web page are determined and prepared for the presentation on the tactile display. Texts are converted to Braille and graphics are converted to monochrome presentation. Therefor the Java algorithms of the first browser are used directly. Furthermore the compound style of each web page element is computed so that it can be presented to the user. When the web page finally is rendered on the tactile display the user may apply the same functionalities as described for the first browser. Furthermore the shown graphics can be replaced by their ALT-attributes if existing so that the presentation becomes tight. Currently we are working on offering navigation possibilities directly on the tactile display using its input devices so that for example hyperlinks may be activated directly by a certain gesture on the tactile display. With such gestures navigation including scrolling and page refreshing is possible without using the keyboard [34]. Of course the keyboard is still needed for text input and the usage of short cuts. As already mentioned our new approach has a number of advantages over the first approach. Ordinary browser components will be kept up-to-date by the developers of the underlying browser so that we will only have to care about our special features for the tactile display support. Furthermore other Firefox extensions may be used in combination and so bring the user an even greater benefit. Last but not least the work with our prototype showed that the new browser will be much faster than the first one. Nevertheless at the moment the new browser has some disadvantages over the first one. Till now we only dealt with the presentation of web content on the tactile display. We did not care about the graphical user interface of the browser itself. This becomes a problem when considering for example message boxes popping up to inform the user about some problems with the current web page or dialogs to change the browser settings or to organize bookmarks. The first browser had only a few such dialogs which were fully implemented by us. So we knew all the dialogs and could support them via output on the tactile display or voice output. Using Firefox raises the problem that arbitrary dialogs are possible and must be somehow supported by our extension. So we decided to plan a project realizing full XUL support for our tactile display after finishing our work on the presentation of web pages. Besides the completion of our browser this will give us the chance to implement arbitrary XUL applications fully supported by our tactile display.
5
Tactile Graphics
Graphical information is common on today’s web pages. For a holistic access to the content of web pages it is essential that this information is accessible to blind people. The graphical information on web pages can be distinguished in: – – – – – –
icons illustrations photos 3D graphics mathematical expressions text as graphics
Icons represent symbols that are often used for navigation or for presenting the current state. Illustrations are the main graphical information on the web and can be used for logos, diagrams, menus, maps, etc. Photos are essential in the web because they present the real world components. 3D graphics of products, sights, maps, etc. can be found rarely on the web, but the access for blind people to small models might be useful. Unfortunately mathematical expressions are mostly presented as images which is a strong disadvantage for their access in learning materials. One of the greatest inaccessible shortcomings is textual information encoded as graphics. This is sometimes used to present text in a special font or to hide this information from crawlers that collect information on the web. However, there is a lot of textual information necessary in an image like the captions of diagrams or the labels for certain values. Graphical information in web pages is usually stored as raster graphics. This kind of graphics is used for all kinds of graphics mentioned above except 3D graphics. In the near future more and more icons and illustrations will be encoded as vector graphics. The advantages of this kind of graphics are scalability, small file size and the ability to store shapes, attributes, and meta information in a well defined way. For mathematical expressions the World Wide Web Consortium proposed the Mathematical Markup Language (MathML) based on XML. This language makes it possible to represent formulas for sighted people as well as doing a transformation in a special mathematical notation for blind people. For blind users it is necessary to access graphical information with non-visual devices. The main problems in preparing graphics for blind people are the low spatial resolution and the binary mode (pins up or down) of interactive tactile devices (see section 3). Therefor graphics have to be scaled down and the colors have to be reduced to one foreground color and one background color. Because of the complexity of some images it may be beneficial to explore them part by part. In the following sections we present our approaches for the accessibility of different kinds of graphics on tactile graphics displays which we integrated in our tactile web browser described in section 4. 5.1
Tactile Vector Graphics
Concerning tactile vector graphics our research is based on the Scalable Vector Graphics (SVG) recommendation of the World Wide Web Consortium (W3C) [35].
SVG is an XML application, where shapes and attributes are encoded as plain text. The meta information in SVG e.g. textual content, shape type, descriptions, stroke width, fill and stroke color, etc. can be used for transformation, navigation, and filtering. The tactile output of images in combination with this meta information displayed on the Braille line or offered by voice output makes the exploration of complex images much easier. The transformation of SVG into an accessible form can be very flexible, because entire groups, shapes, attributes and the content of text elements are encoded in XML and can be extracted separately. As tactile devices are restricted in presenting color states (see section 3) the foreground and background color of images has to be determined. Since there is no SVG attribute for background color, we have implemented a heuristic method that tries to find a shape that has approximately the size of the entire graphic. The fill color of this shape is identified as background color. If no shape in an appropriate size could be found, the background color is set to white. All colors similar to the background color are rendered as pins down. All other colors are identified as foreground and are rendered as pins up. This can be inverted interactively. To support the interactive exploration of graphics we implemented exploration methods where the buildup of the graphics can be accumulated incrementally [28]. This mode can be used even within groups as well, to build them up step by step. In every interaction step the user is informed about title, descriptions, and attributes like shape type, color, content of the text shapes on the Braille line and by voice output. Another mode enables the user to view the elements without minding the hide rules. This makes it possible to see a car in one piece, which is partly hidden by a tree. Furthermore the user can zoom into and out of the displayed graphic. In this case the output size can be larger than the size of the tactile display so that scrolling is necessary. Another quite feasible feature in our SVG explorer is the possibility to apply filters to an image. This may help the users to get an overview over an image. One of the filters removes gradients and patterns in fillings. A contour filter removes the fillings of shapes and shows just the edges. This filter is illustrated in figure 7 which shows the image from figure 6 rendered on the tactile display with the contour filter applied. Furthermore color filters can be used to show just shapes of a specific set of colors. A text filter allows navigating sequentially to text elements and shows the position of the text on the tactile display by toggling the state of the associated pins. For implementing the color filters we decided to restrict the selectable colors to a small number. We believe that using too many colors for filtering will not bring any advantages. To match the different colors of an image to the filterable colors we use the ”basic color terms” established by Brent Berlin and Paul Kay in 1969 [2] as default set of colors. The ”basic color terms” build a basis of distinguishable colors that are white, black, gray, red, pink, yellow, green, blue, purple, brown, and orange. This set of colors can be adapted depending on the individual capabilities. In our software environment the RGB colors and SVG
Fig. 6. Part of a SVG that shows a map of europe
Fig. 7. Figure 6 rendered on the tactile display with applied contour filter (inner country borders like between Spain and Portugal are visible)
color keyword names of shapes are assigned to the nearest color of the ”basic color terms” in the L*a*b* color space [21]. For example if the user turns on the green and black color filter, just such shapes are shown that have a similar color to green and black. If the assignment is ambiguous, a color can be assigned to more than one color of the ”basic color terms” [31]. In these filters the color of the stroke and filling is considered separately. Additionally the fill and the stroke color of the shape is output as the (nearest) SVG color keyword name on the Braille line and by voice output.
5.2
Tactile Raster Graphics
In order to reduce true color raster 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. So we have decided to use simple threshold based methods with which we had reasonable success. 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 graphics display. The other values are mapped to pins up. During exploration the user can adapt the width of the range interactively. Another approach maps high luminance values to pins down and low values to pins up on the tactile graphics 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. In the exploration edges in images are very important for blind people. Therefore we have implemented an edge detection filter using the sobel operator. To extract textual information optical character recognition (OCR) techniques can be used, but this is not yet realized in our system. Currently we are working on the implementation of a part by part exploration for raster images like we have realized for vector graphics. Therefor we are using computer vision techniques. In particular new segmentation algorithms may help to explore a raster image in different levels.
5.3
Tactile 3D Graphics
For our method to present three-dimensional graphics to blind people a transformation is needed that extracts the feature lines of the graphics. Joachim Diepstraten, Martin G¨orke, and Thomas Ertl have proposed an approach on how to extract the feature lines of a 3D model [7]. They distinguished feature lines that represent the edges of objects in boundaries, ridges, valleys, and silhouette lines. These feature lines are extracted and converted into line strokes. Figure 8 shows the result of such a transformation. Finally the line strokes are rendered on the tactile graphics display (figure 9). The presentation of the 3D model may be interactively controlled by the user via rotation and zooming [29]. Therefor the users’ input events have to be handled. For each rotation or zooming request the viewpoint on the 3D model is recalculated. Then the new feature lines are extracted and rendered on the tactile graphics display as line strokes. In the case of a reset request the viewpoint is reset to the predefined viewpoint. Because of the perspective projection in the tactile 3D graphics might be more accessible to persons with acquired blindness.
Fig. 8. An armchair rendered as 3D graphic (left), extracted feature lines of the armchair (right)
Fig. 9. The armchair from figure 8 rendered on the tactile display
5.4
Tactile mathematical expressions
The source code of mathematical expressions in MathML is in principle legible for blind 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 necessary that is more legible for blind people. We have implemented a method to transform MathML expressions into LaTeX and into the Stuttgart Mathematical Notation For the Blind (SMFB) by using XSLT-stylesheets and integrated this into our tactile browser [27]. SMFB is a mathematical notation for blind people that has been developed at the University of Stuttgart since 1980 and is encoded in 8-dot Braille [32].
6
Conclusion and Outlook
In this paper we have presented a tactile browser that renders arbitrary web pages to a tactile graphics display that we have described in section 3. This browser will enable blind people to browse the World Wide Web similar to the way sighted users do. During the realization of the first version of our tactile browser a couple of useful concepts were developed considering for example page layout, tables, lists, and the style of web page elements. We developed a SVG explorer which gives blind people the possibility to access scalable vector graphics. This explorer has been integrated in the tactile browser so that it may be used with SVGs embedded in web pages. With the SVG explorer an incremented buildup of SVGs is possible. Furthermore filters can be applied to the SVGs. Since most images in web pages are stored as raster graphics we have also integrated an exploration mode for such graphics into our tactile browser. Therefor we have implemented algorithms to determine the foreground and the background color of images to convert them into monochrome representations. Furthermore an algorithm to extract the contours of raster graphics was integrated. Both algorithms can be controlled interactively. Even 3D graphics can be explored with the tactile browser. Thus, we implemented a method extracting the feature lines of 3D graphics and afterwards displaying them on the tactile display. The model can be rotated and zoomed interactively. In the near future we will finish another prototype of the second version of our tactile browser which is based on a Firefox extension. The new browser will reuse many of the concepts of the first approach. Basing our new browser on Firefox will bring great benefits to the users. For example the new tactile browser will be faster, it will support sessions, cookies, and dynamic content of web pages and last but not least other Firefox extensions may be usable in combination with ours. Furthermore we are going to use computer vision techniques to improve the access in building up raster graphics incrementally. Our next tactile graphics display that we are going to develop will use piezo technology and will be faster, more portable, and enable direct input.
7
Acknowledgments
At first we want to thank Alfred Werner for helping us understanding blind users’ needs, testing our concepts, and developing new ideas with us during lots of very inspiring discussions. We thank Sven Kn¨odler and Kerstin Otte for their work on the tactile web browser and the algorithms. Furthermore we want to thank Gerhard Weber, Waltraud Schweikhardt and the employees of Metec for their works on the tactile graphics display. Last but not least we thank Aaron Leventhal for his work in the Mozilla Accessibility Project and his support during the development of the prototypic Firefox extension.
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