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. 2021 Apr 26;21(9):3028. doi: 10.3390/s21093028

Table 1.

Previous Reviews from Literature.

Year From Techniques Reviewed
2018 [16] Reviewed Myanmar Researched Papers Only.
  • Khin et al. in the year 2018

    • -

      Threshold based approach and bounding box

    • -

      All colors, and conditions images are used

  • Htay et al. in the year 2016

    • -

      Neural Network Method for Plate Localization

    • -

      Noisy, tilted plates or other degraded forms of number plate were not considered em

    • -

      Very limited number of samples tested

  • Sinha et al. in the year 2011

    • -

      Character extraction and recognition

    • -

      Pattern recognition based on fuzzy logic

    • -

      Did not yield good results for skewed plate

  • Bai et al. in the year 2004

    • -

      Hybrid Approach

    • -

      Edge detection and morphological operations

    • -

      Tilted/skewed characters are not tested

ine 2017 [17] This research reviewed various techniques for each stage of ANPR system.
  • License Plate Extraction:

    • -

      Edge information Analysis

    • -

      Probabilistic model

    • -

      Subspace Projection and Probabilistic Neural Network

    • -

      Blob Analysis, Mathematical Morphology

    • -

      Color Space and Geometrical Properties

    • -

      Thresholding, Histogram, Computational Intelligence and Adaptive Boost techniques

  • Segmentation:

    • -

      Gabor transform

    • -

      K-Means Algorithm

    • -

      Tree of Shapes

    • -

      Hidden Markov Chains

  • Recognition:

    • -

      Optical Character Recognition (OCR)

    • -

      Embedded DSP-Platform

    • -

      Pattern match method

    • -

      Computational Intelligence - Neural Networks

2016 [18] Reviewed techniques:
  • Feature salience, Hough Transform, Neural Networks, Histogram techniques, Chin code, Tophat Filtering, Template matching, Matrix mapping, wavelet transform, SVM, Pulse Coupled Neural X Networks, SIFT feature points, Gaussian Filtering and other modified NNs.

2015 [19] Techniques reviewed for each stage:
  • Number Plate Extraction

    • -

      Method 1

      • *

        Sobel based Vertical Edge Detector

      • *

        Sliding window technique, it has the size similar to that of the number plate size

      • *

        Requires prior knowledge of the number plate size

      • *

        Threshold tuning required and needs to setup for each set

    • -

      Method 2

      • *

        Gradient analysis

      • *

        Vertical histogram along with morphology techniques

      • *

        Connected Component Analysis

    • -

      Method 3

      • *

        Geometrical shape of the number plate

  • Character Segmentation Method

    • -

      Pixel projection in which both vertical and horizontal directions employed

    • -

      Fast and robust

    • -

      Dealt with tilt factor by adding additional layer of vertical projection

  • Character Recognition Techniques

    • -

      Method 1

      • *

        Template Matching

      • *

        Adaptive threshold

      • *

        Pixel-wise matching is performed

      • *

        The simplest method known for recognition

    • -

      Method 2

      • *

        Neural Networks classifiers

The performance of these techniques reviewed is summarized in Table 2.