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Proceedings Paper

Acceptable bit-rates for human face identification from CCTV imagery
Author(s): Anastasia Tsifouti; Sophie Triantaphillidou; Efthimia Bilissi; Mohamed-Chaker Larabi
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Paper Abstract

The objective of this investigation is to produce recommendations for acceptable bit-rates of CCTV footage of people onboard London buses. The majority of CCTV recorders on buses use a proprietary format based on the H.264/AVC video coding standard, exploiting both spatial and temporal redundancy. Low bit-rates are favored in the CCTV industry but they compromise the image usefulness of the recorded imagery. In this context usefulness is defined by the presence of enough facial information remaining in the compressed image to allow a specialist to identify a person. The investigation includes four steps: 1) Collection of representative video footage. 2) The grouping of video scenes based on content attributes. 3) Psychophysical investigations to identify key scenes, which are most affected by compression. 4) Testing of recording systems using the key scenes and further psychophysical investigations. The results are highly dependent upon scene content. For example, very dark and very bright scenes were the most challenging to compress, requiring higher bit-rates to maintain useful information. The acceptable bit-rates are also found to be dependent upon the specific CCTV system used to compress the footage, presenting challenges in drawing conclusions about universal ‘average’ bit-rates.

Paper Details

Date Published: 4 February 2013
PDF: 15 pages
Proc. SPIE 8653, Image Quality and System Performance X, 865305 (4 February 2013); doi: 10.1117/12.2004140
Show Author Affiliations
Anastasia Tsifouti, Ctr. for Applied Science and Technology (United Kingdom)
Univ. of Westminster (United Kingdom)
Sophie Triantaphillidou, Univ. of Westminster (United Kingdom)
Efthimia Bilissi, Univ. of Westminster (United Kingdom)
Mohamed-Chaker Larabi, Univ. de Poitiers (France)

Published in SPIE Proceedings Vol. 8653:
Image Quality and System Performance X
Peter D. Burns; Sophie Triantaphillidou, Editor(s)

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