Paper Review :: character_recog_eng.pdf

Category: Overview
File Name: character_recog_eng.pdf
Title: Character recognition Systems for the non-expert


Comments: good for gathering basic ocr knowledge


Quick Notes:
Character recognition systems (CRS) are subsets of pattern recognition systems.

[Patterns / Words]

Input may come from – online or offline devices.

--> CRS components

a] Pre-processing functions
.. noise reduction
.. skeletonisation (thinning)
.. normalization
...... moment invariant techniques
...... fourier descriptions
...... boundary-based techniques
...... vector analysis
.. segmentation

b] accepts pre-processed inputs &
.. extracts characteristic features (feature extraction maps the whole of each input pattern from its original Euclidean spatial system of co-ordinates onto a single point in a feature space. Feature space is defined by N extracted features, i.e. has N dimensions)
{loop, end-points, dot, junction, contour}
...... horizontal & vertical histograms
...... curvature info (slopes) & local extrema of curvature (of line making-up/fitting a word)
...... topological features (loops, dots, junctions)
...... parameters of polynomial (or other) curve fitting functions
...... contour info

c] classification component (e.g. neural net)
.. assign a label to pattern
techniques:
...... rule-based systems
...... decision trees
...... clustering techniques
...... artificial neural networks
...... hidden Markov models

d] post-processing
.. verification (increase level of confidence in classification made)
.. action execution
.. adaptation (reduce gaps between expected & actual performance)
...... ANN (alter own weights)
...... HMM (probabilistic parameters)