Perspective distortion in craniofacial superimposition: logarithmic decay curves mapped mathematically and by practical experiment

Stephan, Carl N. (2015) Perspective distortion in craniofacial superimposition: logarithmic decay curves mapped mathematically and by practical experiment. Forensic Science International, 257 520.e1-520.e8. doi:10.1016/j.forsciint.2015.09.009

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Author Stephan, Carl N.
Title Perspective distortion in craniofacial superimposition: logarithmic decay curves mapped mathematically and by practical experiment
Journal name Forensic Science International   Check publisher's open access policy
ISSN 1872-6283
0379-0738
Publication date 2015-09-21
Sub-type Article (original research)
DOI 10.1016/j.forsciint.2015.09.009
Open Access Status File (Author Post-print)
Volume 257
Start page 520.e1
End page 520.e8
Total pages 8
Place of publication E Park, Shannon, Clare Ireland
Publisher Elsevier Ireland
Collection year 2016
Language eng
Abstract The superimposition of a face photograph with that of a skull for identification purposes necessitates the use of comparable photographic parameters between the two image acquisition sessions, so that differences in optics and consequent recording of images does not thwart the morphological analysis. Widely divergent, but published, speculations about the thresholds at which perspective distortion becomes negligible (0.5 to >13.5 m) must be resolved and perspective distortion (PD) relationships quantified across their full range to judge tolerance levels, and the suitability of commonly employed contemporary equipment (e.g., 1 m photographic copy-stands). Herein, basic trigonometry is employed to map PD for two same sized 179 mm linear lengths – separated anteroposteriorly by 127 mm – as a function of subject-to-camera distance (SCD; 0.2–20 m). These lengths approximate basic craniofacial heights (e.g., tr-n) and widths (e.g., zy-zy), while the latter approximates facial depth (e.g., n-t). As anticipated, PD decayed in logarithmic and continuous manner with increasing SCD. At SCD of 12 m, the within-image PD was negligible (<1%). At <2.5 m SCD, it exceeded 5% and increased sharply as SCD decreased. Since life size images of skulls and faces are commonly employed for superimposition, a relative 1% perspective distortion difference is recommended as the ceiling standard for craniofacial comparison (translates into a ≤2 mm difference in physiognomical face height). Since superimposition depends on relative comparisons of a photographic pair (not one photograph), there is practically no scenario in superimposition casework where SCDs should be ignored and no single distance at which PD should be considered negligible (even if one image holds >12 m SCD).
Keyword Face
Forensic anthropology population data
Photographic comparison
Skeletal identification
Skull
Video superimposition
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2016 Collection
School of Biomedical Sciences Publications
 
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