Four Light Total Appearance Imaging of Paintings. Berns 00000
Four Light Total Appearance Imaging of Paintings [pdf]Paper  abstract   bibtex   
The total appearance of a painting is defined by its spatially varying spectral reflectance factor, surface macrostructure (depth or surface normal), and surface microstructure (bi-directional reflectance distribution function, BRDF). For paintings with uniform BRDF (e.g., varnished), their total appearance can be measured using equipment commonly found in a photographic studio. Such a system was built and tested for several acrylic- dispersion paintings. The system consisted of three or four strobes affixed with triacetate film lin ear polarizers and a Dual-RGB camera also affixed with a linear polarizer in order to achieve cross polarization. Using the principles of photometric stereo, images of each light source taken sequentially from 45° from the normal and 90° apart annularly (four lights) or 30° from the normal and 120° apart annularly (three lights) were used to measure surface normal. A learning-based algorithm was used to measure colorimetry and spectral reflectance factor. Software, Artviewer , was written to render images for specific geometries and for studio lighting. The system produced images that approximated, but not equaled, conventional studio photography. Because diffuse data were collected, these images are useful for the long-term evaluation of color changes. Evaluation of the surface normal provides new information for the technical examination of artwork.
@misc{berns_four_nodate,
	title = {Four {Light} {Total} {Appearance} {Imaging} of {Paintings}},
	url = {http://www.cis.rit.edu/DocumentLibrary/admin/uploads/CIS000127.pdf},
	abstract = {The  total  appearance  of  a  painting  is  defined  by  its  spatially  
varying  spectral  reflectance  factor,  surface  macrostructure  (depth  
or  surface  normal),  and  surface  microstructure  (bi-directional  
reflectance   distribution   function,
   BRDF).   For   paintings   with   
uniform  BRDF  (e.g.,  varnished),  their  total  appearance  can  be  
measured  using  equipment  commonly  found  in  a  photographic  
studio.  Such  a  system  was  built  and  tested  for  several  acrylic-
dispersion paintings. The system consisted of three or four strobes 
affixed  with  triacetate  film  lin
ear  polarizers  and  a  Dual-RGB  
camera  also  affixed  with  a  linear  polarizer  in  order  to  achieve  
cross  polarization.  Using  the  principles  of  photometric  stereo,  
images  of  each  light  source  taken  sequentially  from  45°  from  the  
normal  and  90°  apart  annularly  (four  lights)  or  30°  from  the  
normal  and  120°  apart  annularly  (three  lights)  were  used  to  
measure  surface  normal.  A  learning-based  algorithm  was  used  to  
measure  colorimetry  and  spectral  reflectance  factor.  Software,  
Artviewer
,  was  written  to  render  images  for  specific  geometries  
and   for   studio   lighting.   The   system   produced   images   that   
approximated,  but  not  equaled,  conventional  studio  photography.  
Because  diffuse  data  were  collected,  these  images  are  useful  for  
the  long-term  evaluation  of  color  changes.  Evaluation  of  the  
surface   normal   provides   new   information   for   the   technical   
examination of artwork.},
	urldate = {2017-02-08TZ},
	author = {Berns},
	note = {00000},
	keywords = {appearance}
}
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