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Handwritten Character Recognition Using Bayesian Decision Theory

Abstract: Appearance acceptance (CR) can break added circuitous botheration in handwritten appearance and achieve acceptance easier. Autography appearance acceptance (HCR) has accustomed all-encompassing absorption in bookish and assembly fields. The acceptance arrangement can be either online or offline. Offline handwritten appearance acceptance is the sub fields of optical appearance acceptance (OCR). The offline handwritten appearance acceptance stages are preprocessing, segmentation, affection abstraction and recognition. Our aim is to advance missing appearance bulk of an offline appearance acceptance appliance Bayesian accommodation theory.

Keywords: Appearance recognition, Optical appearance recognition, Off-line Handwriting, Segmentation, Affection extraction, Bayesian accommodation theory.


The acceptance arrangement can be either on-line or off-line. On-line autography acceptance involves the automated about-face of argument as it is accounting on a adapted digitized or PDA, breadth a sensor picks up the pen-tip movements as able-bodied as pen-up/pen-down switching. That affectionate of abstracts is accepted as agenda ink and can be admired as a activating representation of handwriting. Off-line autography acceptance involves the automated about-face of argument in an angel into letter codes which are accessible aural computer and text-processing applications. The abstracts acquired by this anatomy is admired as a changeless representation of handwriting.

The aim of appearance acceptance is to construe animal bright appearance to apparatus bright character. Optical appearance acceptance is a activity of adaptation of animal bright appearance to apparatus bright appearance in optically scanned and digitized text. Handwritten appearance acceptance (HCR) has accustomed all-encompassing absorption in bookish and assembly fields.

Bayesian accommodation access is a axiological statistical access that quantifies the tradeoffs amid assorted decisions appliance probabilities and costs that accompany such decision.

They broken the accommodation activity into the afterward bristles steps:

Identification of the problem.

Obtaining all-important information.

Production of accessible solution.

Evaluation of such solution.

Selection of a activity for performance.

They additionally accommodate a sixth date accomplishing of the decision. In the absolute access missing abstracts cannot be acceptance which is advantageous in acceptance absolute data. In our access we are acceptance the missing words appliance Bayesian classifier. It aboriginal classifier the missing words to access abbreviate error. It can balance as abundant absurdity as possible.

Related Work

The history of CR can be traced as aboriginal as 1900, aback the Russian scientist Turing attempted to advance an aid for the visually bedridden [1]. The aboriginal appearance recognizers appeared in the boilerplate of the 1940s with the development of agenda computers. The aboriginal assignment on the automated acceptance of characters has been concentrated either aloft machine-printed argument or aloft a baby set of well-distinguished handwritten argument or symbols. Machine-printed CR systems in this aeon about acclimated arrangement akin in which an angel is compared to a library of images. For handwritten text, low-level angel processing techniques accept been acclimated on the bifold angel to abstruse affection vectors, which are again fed to statistical classifiers. Successful, but accountable algorithms accept been implemented mostly for Latin characters and numerals. However, some studies on Japanese, Chinese, Hebrew, Indian, Cyrillic, Greek, and Arabic characters and numerals in both machine-printed and handwritten cases were additionally able [2].

The bartering appearance recognizers were accessible in the 1950s, aback cyberbanking tablets capturing the x-y alike abstracts of pen-tip movement was aboriginal introduced. This accession enabled the advisers to assignment on the on-line autography acceptance problem. A acceptable antecedent of references for on-line acceptance until 1980 can be begin in [3].

Studies up until 1980 suffered from the abridgement of able computer accouterments and abstracts accretion devices. With the access of advice technology, the ahead developed methodologies begin a absolute abundant ambiance for accelerated advance accession to the statistical methods. The CR assay was focused basically on the appearance acceptance techniques afterwards appliance any semantic information. This led to an aerial absolute in the acceptance rate, which was not acceptable in abounding applied applications. Absolute assay of CR assay and development during this aeon can be begin in [4] and [3] for off-line and on-line cases, respectively.

The absolute advance on CR systems is able during this period, appliance the new development accoutrement and methodologies, which are empowered by the continuously growing advice technologies.

In the aboriginal 1990s, angel processing and arrangement acceptance techniques were calmly accumulated with bogus intelligence (AI) methodologies. Advisers developed circuitous CR algorithms, which accept high-resolution ascribe abstracts and crave all-encompassing cardinal crunching in the accomplishing phase. Nowadays, in accession to the added able computers and added authentic cyberbanking equipments such as scanners, cameras, and cyberbanking tablets, we accept efficient, avant-garde use of methodologies such as neural networks (NNs), hidden Markov models (HMMs), down-covered set reasoning, and accustomed accent processing. The contempo systems for the machine-printed off-line [2] [5] and bound vocabulary, user-dependent on-line handwritten characters [2] [12] are absolutely satisfactory for belted applications. However, there is still a continued way to go in adjustment to ability the ultimate ambition of apparatus simulation of chatty animal reading, abnormally for airy on-line and off-line handwriting.

Bayesian accommodation Access (BDT), one of the statistical techniques for arrangement classification, to analyze anniversary of the ample cardinal of black-and-white ellipsoidal pixel displays as one of the 26 basal belletrist in the English alphabet. The appearance images were based on 20 altered fonts and anniversary letter aural 20 fonts was about adulterated to aftermath a book of 20,000 altered instances [6].

Existing System

In this overview, appearance acceptance (CR) is acclimated as an awning term, which covers all types of apparatus acceptance of characters in assorted appliance domains. The overview serves as an amend for the advanced in the CR field, emphasizing the methodologies adapted for the accretion needs in anew arising areas, such as development of cyberbanking libraries, multimedia databases, and systems which crave autography abstracts entry. The abstraction investigates the administration of the CR research, allegory the limitations of methodologies for the systems, which can be classified based aloft two aloft criteria: 1) the abstracts accretion activity (on-line or off-line) and 2) the argument blazon (machine-printed or handwritten). No bulk in which chic the botheration belongs, in general, there are bristles aloft stages Figure1 in the CR problem:

1) Preprocessing

2) Segmentation

3) Affection Extraction

4) Recognition

5) Post processing

3.1. Preprocessing

The raw data, depending on the abstracts accretion type, is subjected to a cardinal of basal processing achieve to achieve it accessible in the anecdotic stages of appearance analysis. Preprocessing aims to aftermath abstracts that are accessible for the CR systems to achieve accurately.

The capital objectives of preprocessing are:

1) Babble reduction

2) Normalization of the data

3) Compression in the bulk of advice to be retained.

In adjustment to achieve the aloft objectives, the afterward techniques are acclimated in the preprocessing stage.



Splits Words

Feature Extraction


Post processing

Figure 1. Appearance recognition

3.1.1 Babble Reduction

The noise, alien by the optical scanning accessory or the autograph instrument, causes broken band segments, bumps and gaps in lines, abounding loops, etc. The distortion, including bounded variations, rounding of corners, dilation, and erosion, is additionally a problem. Above-mentioned to the CR, it is all-important to annihilate these imperfections. Hundreds of accessible babble abridgement techniques can be categorized in three aloft groups [7] [8]:

a) Filtering

b) Morphological Operations

c) Babble Modeling

3.1.2 Normalization

Normalization methods aim to abolish the variations of the autograph and access connected data. The afterward are the basal methods for normalization [4] [10][16].

a) Skew Normalization and Baseline Extraction

b) Slant Normalization

c) Admeasurement Normalization

3.1.3 Compression

It is able-bodied accepted that classical angel compression techniques transform the angel from the amplitude breadth to domains, which are not acceptable for recognition. Compression for CR requires amplitude breadth techniques for attention the appearance information.

a) Threshold: In adjustment to abate accumulator requirements and to access processing speed, it is generally adorable to represent gray-scale or blush images as bifold images by acrimonious a beginning value. Two categories of beginning exist: all-around and local. All-around beginning picks one beginning bulk for the absolute certificate angel which is generally based on an admiration of the accomplishments akin from the acuteness histogram of the image. Bounded (adaptive) beginning use altered ethics for anniversary pixel according to the bounded breadth information.

b) Thinning: While it provides a amazing abridgement in abstracts size, abrasion extracts the appearance advice of the characters. Abrasion can be advised as about-face of off-line autography to about on-line like data, with affected branches and artifacts. Two basal approaches for abrasion are 1) pixel astute and 2) epitome astute abrasion [1]. Pixel astute abrasion methods locally and iteratively activity the angel until one pixel advanced skeleton remains. They are absolute acute to babble and may batter the appearance of the character. On the alternative hand, the no pixel astute methods use some all-around advice about the appearance during the thinning. They aftermath a assertive boilerplate or centerline of the arrangement anon afterwards analytical all the alone pixels. In clustering-based abrasion adjustment defines the skeleton of appearance as the array centers. Some abrasion algorithms analyze the atypical credibility of the characters, such as end points, cantankerous points, and loops. These credibility are the antecedent of problems. In a epitome astute thinning, they are handled with all-around approaches. A assay of pixel astute and epitome astute abrasion approaches is accessible in [9].

3.2. Segmentation

The preprocessing date yields a “clean” certificate in the faculty that a acceptable bulk of appearance information, aerial compression, and low babble on a normalized angel is obtained. The abutting date is segmenting the certificate into its subcomponents. Assay is an important date because the admeasurement one can ability in break of words, lines, or characters anon affects the acceptance bulk of the script. There are two types of segmentation: alien segmentation, which is the abreast of assorted autograph units, such as paragraphs, sentences, or words, and centralized segmentation, which is the abreast of letters, abnormally in cursively accounting words.

1) Alien Segmentation: It is the best analytical allotment of the certificate analysis, which is a all-important footfall above-mentioned to the off-line CR Although certificate assay is a almost altered assay breadth with its own methodologies and techniques, segmenting the certificate angel into argument and non argument regions is an basic allotment of the OCR software. Therefore, one who works in the CR acreage should accept a accepted overview for certificate assay techniques. Page blueprint assay is able in two stages: The aboriginal date is the structural analysis, which is anxious with the assay of the angel into blocks of certificate apparatus (paragraph, row, word, etc.), and the additional one is the anatomic analysis, which uses location, size, and assorted blueprint rules to characterization the anatomic agreeable of certificate apparatus (title, abstract, etc.) [12].

2) Centralized Segmentation: Although the methods accept developed appreciably in the aftermost decade and a array of techniques accept emerged, assay of cursive calligraphy into belletrist is still an baffling problem. Appearance assay strategies are broken into three categories [13] is Explicit Segmentation, Implicit Assay and Mixed Strategies.

3.3. Affection Extraction

Image representation plays one of the best important roles in a acceptance system. In the simplest case, gray-level or bifold images are fed to a recognizer. However, in best of the acceptance systems, in adjustment to abstain added complication and to access the accurateness of the algorithms, a added bunched and adapted representation is required. For this purpose, a set of appearance is extracted for anniversary chic that helps analyze it from alternative classes while absolute invariant to adapted differences aural the class[14]. A acceptable assay on affection abstraction methods for CR can be begin [15].In the following, hundreds of certificate angel representations methods are categorized into three aloft groups are All-around Transformation and Series Expansion, Statistical Representation and Geometrical and Topological Representation .

3.4. Acceptance Techniques

CR systems abundantly use the methodologies of arrangement recognition, which assigns an alien sample into a predefined class. Numerous techniques for CR can be advised in four accepted approaches of arrangement recognition, as adapted in [16] are Arrangement matching, Statistical techniques, and Structural techniques and Neural networks.

3.5. Post Processing

Until this point, no semantic advice is advised during the stages of CR. It is able-bodied accepted that bodies apprehend by ambience up to 60% for absent-minded handwriting. While preprocessing tries to “clean” the certificate in a assertive sense, it may abolish important information, aback the ambience advice is not accessible at this stage. The abridgement of ambience advice during the assay date may account alike added astringent and irreversible errors aback it yields absurd assay boundaries. It is bright that if the semantic advice were accessible to a assertive extent, it would accord a lot to the accurateness of the CR stages. On the alternative hand, the absolute CR botheration is for free the ambience of the certificate image. Therefore, appliance of the ambience advice in the CR botheration creates a craven and egg problem. The assay of the contempo CR assay indicates accessory improvements aback alone appearance acceptance of the appearance is considered. Therefore, the assimilation of ambience and appearance advice in all the stages of CR systems is all-important for allusive improvements in acceptance rates.

The proposed Arrangement Architecture

The proposed assay alignment for off-line cursive handwritten characters is declared in this area as apparent in Amount 2.

4.1 Preprocessing

There abide a accomplished lot of tasks to complete afore the absolute appearance acceptance operation is commenced. These above-mentioned tasks achieve assertive the scanned certificate is in a acceptable anatomy so as to ensure the ascribe for the consecutive acceptance operation is intact. The activity of adorning the scanned ascribe angel includes several achieve that include: Binarization, for transforming gray-scale images in to atramentous & white images, abrading noises, Skew Correction- performed to adjust the ascribe with the alike arrangement of the scanner and etc., The preprocessing date comprise three steps:

(1) Binarization

(2) Babble Removal

(3) Skew Correction

Scanned Certificate Image

Feature Extraction

Bayesian Accommodation Theory

Training and Recognition



Noise Removal

Skew correction





Recognition o/p

Figure 2. Proposed Arrangement Architecture

4.1.1 Binarization

Extraction of beginning (ink) from the accomplishments (paper) is alleged as threshold. Typically two peaks comprise the histogram gray-scale ethics of a certificate image: a aerial aiguille akin to the white accomplishments and a abate aiguille agnate to the foreground. Fixing the beginning bulk is free the one optimal bulk amid the peaks of gray-scale ethics [1]. Anniversary bulk of the beginning is approved and the one that maximizes the archetype is alleged from the two classes admired as the beginning and aback arena points.

4.1.2 Babble Removal

The attendance of babble can bulk the ability of the appearance acceptance system; this affair has been dealt abundantly in certificate assay for typed or machine-printed documents. Babble may be due the poor affection of the certificate or that accumulated whilst scanning, but whatever is the account of its attendance it should be removed afore added Processing. We accept acclimated boilerplate clarification and Wiener clarification for the abatement of the babble from the image.

4.1.3 Skew Correction

Aligning the cardboard certificate with the according arrangement of the scanner is capital and alleged as skew correction. There abide a countless of approaches for skew alteration accoutrement correlation, projection, profiles, Hough transform and etc.

For skew bend apprehension Cumulative Scalar Products (CSP) of windows of argument blocks with the Gabor filters at altered orientations are calculated. Alignment of the argument band is acclimated as an important affection in ciphering the skew angle. We account CSP for all accessible 50X50 windows on the scanned certificate angel and the boilerplate of all the angles acquired gives the skew angle.

4.2 Segmentation

Segmentation is a activity of adapted lines, words, and alike characters of a duke accounting or machine-printed document, a acute footfall as it extracts the allusive regions for analysis. There abide abounding adult approaches for segmenting the arena of interest. Straight-forward, may be the assignment of segmenting the curve of argument in to words and characters for a apparatus printed abstracts in adverse to that of handwritten document, which is quiet difficult. Analytical the accumbent histogram contour at a abate ambit of skew angles can achieve it. The capacity of line, chat and appearance assay are discussed as follows.

4.2.1 Band Segmentation

Obviously the ascenders and descanters frequently bisect up and bottomward of the adjoining lines, while the curve of argument ability itself agitate up and down. Anniversary chat of the band resides on the abstract band that bodies use to accept while autograph and a adjustment has been formulated based on this angle apparent fig.3.

Figure 3. Band Segmentation

The bounded minima credibility are calibrated from anniversary Component to almost this abstract baseline. To account and assort the minima of all apparatus and to admit altered handwritten curve absorption techniques are deployed.

4.2.2 Chat and Appearance Segmentation

The activity of chat assay succeeds the band break task. Best of the chat assay issues usually apply on acute the gaps amid the characters to analyze the words from one addition other. This activity of acute words emerged from the angle that the spaces amid words are usually beyond than the spaces amid the characters in fig 4.

Figure 4. Chat Segmentation

There are not abounding approaches to chat assay issues dealt in the literature. In animosity of all these perceived conceptions, exemptions are quiet accepted due to flourishes in autograph styles with arch and abaft ligatures. Alternative methods not depending on the apparent ambit amid components, incorporates cues that bodies use. Meticulous assay of the aberration of agreement amid the adjoining characters as a activity of the agnate characters themselves helps acknowledge the autograph appearance of the author, in agreement of spacing. The assay arrangement comprises the angle of assured greater spaces amid characters with arch and abaft ligatures. Recognizing the words themselves in textual curve can itself advice advance to abreast of words. Assay of words in to its basic characters is accustomed by best acceptance methods. Appearance like ligatures and concavity are acclimated for free the assay points.

4.3 Affection Extraction

The admeasurement accordingly bound in practice, it becomes capital to accomplishment optimal acceptance of the advice stored in the accessible database for affection extraction. Thanks to the arrangement of beeline lines, instead of a set of pixels, it is adorable to represent appearance images in handwritten appearance recognition. Whilst captivation discriminated advice to augment the classifier, ample abridgement on the bulk of abstracts is able through agent representation that food alone two pairs of ordinates replacing advice of several pixels. Vectorization activity is performed alone on base of bi-dimensional angel of a appearance in off-line appearance recognition, as the activating akin of autograph is not available. Reducing the array of cartoon to a distinct pixel requires abrasion of appearance images first. Appearance afore and afterwards Abrasion Afterwards streamlining the appearance to its skeleton, entrusting on an aggressive chase activity of pixels and on a archetype of affection of representation goes on the vectorization process. The aggressive chase activity principally works by analytic for new pixels, initially in the aforementioned administration and on the accepted band articulation subsequently. The chase administration will aberrate progressively from the present one aback no pixels are traced. The activating akin of autograph is retrieved of advance with abstinent akin of accuracy, and that is article of aggressive search. Starting the scanning activity from top to basal and from larboard to right, the starting point of the aboriginal band segment, the aboriginal pixel is identified. According to the aggressive chase principle, defined is the abutting pixel that is acceptable to be congenital in the segment. Accumbent is the absence administration of the articulation advised for aggressive search. Either if the baloney of representation exceeds a analytical beginning or if the accustomed cardinal of pixels has been associated with the segment, the cessation of band articulation occurs. Computing the boilerplate ambit amid the band articulation and the pixels associated with it will crop the baloney of representation. The arrangement of beeline curve actuality represented through ordinates of its two extremities appearance angel representation is automated finally. All the ordinates are connected in accordance to the antecedent amplitude and acme of appearance angel to boldness calibration Variance.

4.4 Bayesian Accommodation Theories

The Bayesian accommodation access is a arrangement that minimizes the allocation error. This access plays a role of a prior. This is aback there is antecedence advice about article that we would like to classify.

It is a axiological statistical access that quantifies the tradeoffs amid assorted decisions appliance probabilities and costs that accompany such decisions. First, we will accept that all probabilities are known. Then, we will abstraction the cases breadth the probabilistic anatomy is not absolutely known. Suppose we apperceive P (wj) and p (x|wj) for j = 1, 2…n. and admeasurement the animation of a angle as the bulk x.

Define P (wj |x) as the a posteriori anticipation (probability of the accompaniment of attributes actuality wj accustomed the altitude of affection bulk x).

We can use the Bayes blueprint to catechumen the above-mentioned anticipation to the afterwards probability

P (wj |x) =

Where p(x)

P (x|wj) is alleged the likelihood and p(x) is alleged the evidence.

Probability of absurdity for this decision

P (w1 |x) if we adjudge w2

P (w2|x) if we adjudge w1

P (error|x) = {

Average anticipation of error

P (error) =

P (error) =

Bayes accommodation aphorism minimizes this absurdity because

P (error|x) = min {P (w1|x), P (w2|x)}

Let {w1. . . wc} be the bound set of c states of attributes (classes, categories). Let {α1. . . αa} be the bound set of a accessible actions. Let λ (αi |wj) be the accident incurred for demography activity αi aback the accompaniment of attributes is wj. Let x be the

D-component vector-valued accidental capricious alleged the affection vector.

P (x|wj) is the class-conditional anticipation body function. P (wj) is the above-mentioned anticipation that attributes is in accompaniment wj. The afterwards anticipation can be computed as

P (wj |x) =

Where p(x)

Suppose we beam x and booty activity αi. If the accurate accompaniment of attributes is wj, we acquire the accident λ (αi |wj).

The accepted accident with demography activity αi is

R (αi |x) = which is additionally alleged the codicillary risk.

The accepted accommodation aphorism α(x) tells us which activity to booty for ascertainment x. We appetite to acquisition the accommodation aphorism that minimizes the all-embracing risk

R =

Bayes accommodation aphorism minimizes the all-embracing accident by selecting the activity αi for which R (αi|x) is minimum. The consistent minimum all-embracing accident is alleged the Bayes accident and is the best achievement that can be achieved.

4.5 Simulations

This area describes the accomplishing of the mapping and bearing model. It is implemented appliance GUI (Graphical User Interface) apparatus of the Java programming beneath Eclipse Tool and Database autumn abstracts in Microsoft Access.

For accustomed Handwritten angel appearance and catechumen to Binarization, Babble Abolish and Assay as apparent in Amount 5(a). Again afterwards accomplish Affection Extraction, Acceptance appliance Bayesian accommodation access as apparent in Figure5(b).

Figure 5(a) Binarization, Babble Abolish and Segmentation

Figure 5(b) Acceptance appliance Bayesian accommodation theory

5. After-effects and Discussion

This database contains 86,272 chat instances from an 11,050 chat concordance accounting bottomward in 13,040 argument lines. We acclimated the sets of the criterion assignment with the bankrupt cant IAM-OnDB-t13. There the abstracts is broken into four sets: one set for training; one set for acceptance the Meta ambit of the training; a additional validation set which can be used, for example, for optimizing a accent model; and an absolute analysis set. No biographer appears in added than one set. Thus, a biographer absolute acceptance assignment is considered. The admeasurement of the cant is about 11K. In our experiments, we did not accommodate a accent model. Thus the additional validation set has not been used.

Table1. Shows the after-effects of the four alone acceptance systems [17]. The chat acceptance bulk is artlessly abstinent by adding the cardinal of actual accustomed words by the cardinal of words in the transcription.

We presented a new Bayesian accommodation access for the acceptance of handwritten addendum accounting on a whiteboard. We accumulated two off-line and two online acceptance systems. To amalgamate the achievement sequences of the recognizers, we incrementally accumbent the chat sequences appliance a accepted cord akin algorithm. Evaluation of proposed Bayesian accommodation access with absolute acceptance systems with account to blueprint is apparent in amount 6.

Table 1. After-effects of four individuals acceptance systems



Recognition rate


1st Offline

Hidden Markov Method



1st Online




2nd Online




2nd Offline

Bayesian Accommodation theory



Figure 6 Evaluation of Bayesian accommodation access with absolute acceptance systems

Then anniversary achievement position the chat with the best occurrences has been acclimated as the ¬nal result. With the Bayesian accommodation access could statistically signi¬cantly access the accuracy.

6. Conclusion

We achieve that the proposed access for offline appearance recognition, which fits the ascribe appearance angel for the adapted affection and classifier according to the ascribe angel quality. In absolute arrangement missing characters can’t be identified. Our access appliance Bayesian Accommodation Theories which can allocate missing abstracts finer which abatement absurdity in analyze to hidden Markova model. Significantly increases in accurateness levels will begin in our adjustment for appearance recognition

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