There are already various transliteration systems for Arabic based scripts to represent in Roman. However all of them aims to represent phonemes in transliteration, without paying attention to different visual elements. When we are manually transcribing these texts, the method is fine. However when we try to represent visual elements in scanned handwritten documents, we faced some problems regarding these transliteration systems.
Since conventional systems aim to represent phonemes, a correct reading is necessary and this requires expertise in the represented language. For Ottoman this is a deeper problem since the writing system is not actively used.
Labels should correspond to classes in classification of visual elements. For example, in some cases we label ى ,ي and ـيـ identically as y but their visual features are distinct from each other. In other cases, an identical letter is coded as y, e or i albeit represented identically in visual terms, because of their difference in reading. This makes visual classes mixed, fuzzy and any measurement of performance does give little clue about the effectiveness of features or classifiers.
Here we document a new transliteration system for visual items in Ottoman Turkish. In this work, our aim is to provide a simple visual approach to transliteration and then devise necessary conversion tables into phonetic transliteration or transcription systems.
Except numerals, words in Arabic based writing systems is composed of items in two categories. The first category is a large letter group composed of a continuous movement of pen, like کلمه. The other category are the smaller elements like dots and diacritics found around these larger items.
A visual transliteration should represent distinct visual elements differently. In order to keep simplicity in labeling and application, dotless letters will be used as base letters and the other letters will be written in terms of these dotless items.
A full letter code is composed from one base letter code and an optional set of diacritic codes. The base letter code is a small Roman letter. The diacritic codes have two parts, the first part is one of o, u or i, which mean over, under or ligature respectively. The second part of diacritic code shows the type of diacritics and is a string of digits or letters. A full letter code conforms the following regular expression: [a-h,j-n,p-t,v-z](([ou][0-9]+)|(i[a-h,j-n,p-t,v-z]))*
The letters o, u and i are not used as base letter codes so there is no ambiguity in parsing the elements.
The tables for all visual elements can be found in Tables tab:baseletters, tab:diacritics and tab:numerals.
|Letter Shape||Transliteration||Used in Letters|
|ٮ||b||ب, ت, ث, ن, پ, یـ|
|ح||x||ح, خ, ج, چ|
Table: The Transliterations of Base Letters
|1||Dot of ب, ن or خ|
|2||Dots of ق, ت or یـ|
|3||Dots of ث, ش or چ|
|5||ء hamza and also in ك|
|8||ـّ shadda ||
|0||ـْ sukun ||
|6||ـٓ madda ||
|7||/ sign above گ|
|4||ـَ fatha and ـِ kasra ||
|9||ـُ damma ||
|44||ـً fathatan and ـٍ kasratan ||
|99||ـٌ dammatan ||
Table: Transliterations for Diacritics
Table: Transliterations for Numerals
The advantages for using this transliteration instead of a phonetic transliteration can be summarized as follows:
Representing visual elements in a phonetic way is not an optimal representation for Computer Vision research. The information from phonetic representation slips into visual information which results classes that bear no direct connection with visual features. In turn these classes become harder to classify and understand.
The transliteration system described in this paper does not need expertise in the language. Anyone who recognize the letters should be able to transliterate word images.
It's possible to denote single elements which does not represent a sound in the language with visual transliteration. No transliteration system for Arabic and similar languages represent diacritics as in Table tab:diacritics. This is important for Computer Vision, since these items are as legitimate visual elements on a paper as others. Without independent representation, these items should be represented along with others and their classification cannot be done independently.
The system is much more flexible than a phonetic transliteration system. It allows to develop new letter signs by combining existing diacritics with base letters. For example ﭪ is a letter not found in historical documents, but can be seen in modern Arabic to represent v sound. Although not thought beforehand this can be represented as fo3 in the system we describe. There are also writing variations, for example, in Maghribi (Western) Arabic. the letter ف is written as ڢ but phonetically identical. In a phonetic transliteration this difference is lost, but the visual transliteration is able to represent the usual case with fo1 and the specific case with fu1.
It is common in handwriting to attribute diacritics of one letter to another. For example three dots in the middle of سر may be read as شر or سژ. In a phonetic transliteration system the first might be represented as şr and the second is sj. This leads to a complexity to describe such middle cases. In visual transliteration system, these two are represented as so3r and sro3 in which we are able to write rules that exchange o3 between neighboring letters and decide for a best reading in later stages.
In handwriting and print, diacritics are especially written loosely. For example three dots above ث is written as three separate dots in print, but usually contracted as \asciicirc in handwriting. For the print case, we can have so1o1o1 denoting three dots separately while for the handwriting case so3 is used and in an upper level, the former is converted to the latter by a rule specifying three separate dots mean a single three dot.
Table tab:ottoman-letters all letters of Ottoman alphabet.
|Ottoman Letter||Transliteration||Ottoman Letter||Transliteration \\|
|ا||e||اَ |||eo4 ||
|اِ |||eu4 |||اُ |||o9 ||
Table: Ottoman Letters and Transliterations}