EFFECTS OF AMBIENT LIGHT, CAMCORDER SETTINGS, AND AUTOMATED LICENSE PLATE READER SETTINGS ON PLATE TRANSCRIPTION RATES

The ability of an automated license plate reading (ALPR) system to convert video images of license plates into computer records depends on many factors. Of these, two are readily controlled by the operator: the quality of the video images captured in the field and the internal settings of the ALPR used to transcribe these images. A third factor, the light conditions under which the license plate images are acquired, is less easily managed, especially when camcorders are used in the field under ambient light conditions. A set of experiments was conducted to test the effects of ambient light conditions, video camcorder adjustments, and internal ALPR settings on the percent of correct reads attained by a specific type of ALPR, one whose optical character recognition process is based on template matching. Images of rear license plates were collected under four ambient light conditions: overcast with no shadows, and full sunlight with the sun in front of the camcorder, behind the camcorder, and orthogonal to the line of sight. Three camcorder exposure settings were tested. Two of the settings made use of the camcorder's internal light meter, and the third relied solely on operator judgment. The license plates read ranged from 41% to 72%, depending most strongly on ambient light conditions. In all cases, careful adjustment of the ALPR led to significantly improved read rates over those obtained by using the manufacturer's recommended default settings. Exposure settings based on the operator's judgment worked best in all instances.

• Record URL:
  https://doi.org/10.3141/1804-08
• Summary URL:
  http://scholar.google.com/scholar_lookup?title=EFFECTS+OF+AMBIENT+LIGHT%2c+CAMCORDER+SETTINGS%2c+AND+AUTOMATED+LICENSE+PLATE+READER+SETTINGS+ON+PLATE+TRANSCRIPTION+RATES&author=M.+Plotnikov&author=P.+Shuldiner&publication_year=2002
• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/isbn/0309077303
• Supplemental Notes:
  • This paper appears in Transportation Research Record No. 1804, Transportation Data and Information Technology Research.
• Corporate Authors:

  Transportation Research Board

  500 Fifth Street, NW
  Washington, DC  United States  20001
• Authors:
  • Plotnikov, M
  • Shuldiner, P W
• Publication Date: 2002

Language

• English

Media Info

• Features: Figures; References; Tables;
• Pagination: p. 56-61
• Serial:
  • Transportation Research Record
  • Issue Number: 1804
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Automatic license plate readers; Field studies; Judgment (Human characteristics); Motor skills; Operators (Persons); Video imaging detectors
• Uncontrolled Terms: Ambient light conditions; Camcorder settings
• Subject Areas: Highways; Planning and Forecasting; I72: Traffic and Transport Planning;

Filing Info

• Accession Number: 00935375
• Record Type: Publication
• ISBN: 0309077303
• Files: TRIS, TRB, ATRI
• Created Date: Dec 10 2003 12:00AM