Go to previous article
Go to next article
Return to 1999 Conference Table of Contents
Jan Halousek Ph.D.
Merit, Czech Republic
Sensitive fingers of blind readers were the only decoding tool and quality evaluation measure of embossed Braille until present. Improvements presented in this article are intended for the blind users as well as for the sighted people and Braille producers:
Sighted people, who are not experienced tactile Braille readers, are able to recognize the Braille coded text from its visual appearance. Recognition is slow and tiring, but possible. Similar information is available from the standard flatbad scanner. Results of transfer of the tiring job to the computer are presented in this article.
Scanned image of the double-sided embossed Braille sheet consists of a "grid" of only limited types of dot patterns. Image of a dot formed towards the scanner window differs from the image of dot formed backwards. Thus, the picture of embossed Braille sheet captured by a standard flatbed scanner contains information about the Braille coded text. The whole „OBR" process is divided into several steps: dot matrix recognition, page merging, Braille to Braille copy function, Braille to ASCII translation, text processing.
Recognition of the dot matrix is the core of the „OBR" system. Its design is based upon advanced methods of mathematics, statistics and computer vision. However, the main principles used in the "OBR" are as follows:
Result of the dot matrix recognition is the internal Braille representation presented to the user in a form of a "locked" ASCII text, converted by one of the „OBR - Grammars", explained more in detail in chapter 1.c. of this paper. The reason to keep the text in a Braille representation is to keep it open to the changes of translation rules – the „OBR - Grammars" as well as for the merging process. The Braille representation can cope with operations like turn page upside down.
Page merging function makes possible to process Braille sheets larger than the scanner window. The merging function automatically "pastes" the individual overlapping scans of the same Braille document into a ONE "computer image" . Core of the merging process is a highly sophisticated system of fitting the same segments of the individual scans together. The only requirement for the merging function is a reasonable overlapping of individual scans – several Braille cells column strip or several lines strip is usually enough.
However, it has to be pointed out on this place, that orientation of the subsequent partial scans of the document is not important – even changing of the face and reverse sides of the document scanned makes no difficulties for the automatic merging process of the OBR. However, combination of different scanning directions and orientations can, in some very difficult cases of recognition of worn-up originals, even to improve the recognition ability of the OBR system. The orientation independent merging process is advantageous also for the visually impaired operators.
An opportunity to economize up to several percents of merging processing time is available on the "OBR" dialog by pre-definition of the Braille line scanning direction. The operator’s task in the merging process is to watch the provisional „locked text" on the screen and to estimate which part of the document is missing and to move the document on scanner in proper direction for the next scan. The Braille document dimension is not limited within the „OBR" system – the merging process can be repeated without limitation.
The Braille to Braille copy function is implemented namely for the cases, where the ASCII format decoding is not required or has no principal sense – like in the Braille music notation copying. The Index Braille printer is supposed to be used as embosser for the copy function. This simple function assures the one-to-one copy including all the formatting features of the original – however, the same paper dimensions are essential.
The so called „Grammars" as a higher abstraction of the commonly used „Braille tables" are used as mathematical model for conversion process of Braille cell to ASCII character. The reason is, that the real decoding process is often complicated by a contextual dependence: The prefix changing lower case letters to capitals is a typical, but not the only one example. One of the advantages of the „OBR - Grammars" is a modular concept of decoding, which makes possible to combine different habits of local coding manners for figures, capitals, shortcuts and other by a quite simple selection on the computer dialog screen. The resulting compilation of „Grammar modules" can be saved and used as a „New Grammar". The concept of „OBR - Grammars" is used also in the decoding translation of the US „Grade Two" Braille, which is implemented in the system.
However, it has to be considered, that some of the Braille coding habits are, unfortunately, ambiguous – several ASCII to Braille coding rules have the same result in the Braille transcription, the sense of which is very deeply context dependent. A typical example is a full stop, space and/or hyphen in a telephone number figure string or in a chapter numbering system. Solution of such ambiguities remains on the proof-reading in the „OBR". Their full solution would be over-sophisticated and potentially even more confusing.
The text, recovered by the OBR System is ready for all the Windows applications, however, the OBR themselves is equipped with basic text processing features, making the modifications, proofreading corrections and editing easy and convenient.
The OBR System is ready for everyday use for both the sighted and the blind communities. The OBR System is a typical product of international cooperation – The product was defined and managed by Merit, it was developed by Neovision, both the Czech Republic, and it is marketted and distributed by the Swedish company Index Braille.
Quality of tactile Braille embossed on a paper carrier was always a matter of unlimited discussions and subjective feelings, which usually differ deeply. Aim of our work was to specify several measurable parameters describing the Braille paper and the dot formed on it by objective measures quantifying it from the points of view of the blind users including the parameter of dot durability as well as from the point of view of Braille producers and production economy.
Braille dot geometry objective measurement is complicated due to its nature: The dot is a small, threedimensional damageable and delicate object. Reliability of classic mechanical measurement methods is very limited due to easy deformations of cellulose fibers forming the dot by the measuring device touch.
Only rough estimate of dot height is feasible by mechanical measuring means. The best reproducibility of data is achieved, if a "drop-down" method is used: The first distance value, through which the sheet falls slowly down, slightly braked by dot friction is taken as a "dot height" value. The forces, deforming the dot fibers are more or less defined that way.
More precise results of Braille dot shape measurement can be achieved only by contactless optical methods. Two mutually perpendicular projections of the dot, crossing its main axes, describe the dot shape well enough: The dot height, the medium dot foot diameter, dot centricity and the dot flank slope can be evaluated. Electronic measuring microscope using the shadow of the dot – the device called "OPAS", product of the Czech Co. Neovision proved to be an efficient tool for the Braille dot shape measurement and computer evaluation.
The delicate nature of the Braille dot embossed on the paper makes the dot mechanical stability essential parameter from both the users as well as producers points of view: Readability of Braille after repeated reading as well as its readability after its storage with some damaging force applied to it is often demanded. The standard usual solution is use of thicker Braille paper with higher grammage – however that can be the expensive solution. It is doubtless, that different embossing technologies and different Braille paper materials result in very different dot "stability".
"Dot Deformation Resistivity " – the "DDR" parameter has been developed by Merit for objective quantification of embossed Braille. The "DDR" is defined as ratio of force, deforming the dot in the direction perpendicular to its axis, and the dot height decrease, caused by the force concerned. It is expressed in Newton per millimeter values. The higher is the "DDR", the more stable is the dot.
Experience of the "DDR" measurements have proven that the Braille papers of the same grammage per meter, common on the world market, differ up to three times in the "DDR" values – in other words the Braille production economy performs a serious hidden reserve if the "DDR" would be considered.
Embossing Braille directly on single sheets brings a lot of production advantages, however quite often also a lot of difficulties. The "doublefeeds" are the sources of trouble, the unreliable automatic sheet-feeder operation with some of the Braille paper products. Physical reasons of the "doublefeeds" have been disclosed by our research: The sheets of paper pile in the automatic sheet-feeder are stuck to each other by a static friction. The last one is fixed on the sheet-feeder bottom by a high friction material. The first sheet is in addition to its static friction braked by a force of small mechanical detent stop with nonlinear function, used on the paper edge or corners.
Automatic sheet-feeder picks up the first sheet from the paper stack, grasping it by high friction rubber rollers by a force, which overcomes the nonlinear detent and brings the first sheet to movement. Thus the movement of the first sheet against the next – second – sheet changes its friction from the higher static friction to a lower dynamic friction. The dynamic friction must be low enough to keep the force influencing the second sheet below the static brake force of the mechanical detent stop. Understanding this physics makes clear the technical requirement on the Braille paper for reliable operation of automatic single sheet-feeders: The static to dynamic friction coefficients ratio must be high enough, experience has proven the value of approximately higher than 1,2 .
Braille paper types ExTaP and EmBoss have been developed in the Czech Republic and are supplied by Merit, performing the static to dynamic friction over 1,3 assuring thus reliable operation of automatic single sheet-feeders.
The most important parts of embossing device – the forming matrixes – are heavily loaded by the surface contact with the Braille paper. The expensive matrixes are in many cases destroyed by abrasive influence of Braille paper. The reason is content of mineral abrasives in most of the Braille paper products available on the world market. Usually melted limestone or kaolin (china clay) are used in several weight percents of the products.
Braille paper types ExTaP and EmBoss have been developed in the Czech Republic and are supplied by Merit, having zero content of mineral abrasives – the "ash content" is less than 1 percent. Expensive frequent embosser maintenance can be avoided if proper Braille paper material is used.
Economy improvements are opened for the blind users as well as for the Braille production by the present advances:
Objective measurement of "Dot Deformation Resistivity" of Braille dots makes possible to choose the proper Braille paper and its grammage.
Authors are ready to help to those, who could profit from the research presented in this paper.
Go to previous article
Go to next article
Return to 1999 Conference Table of Contents
Return to Table of Proceedings