View
3
Download
0
Category
Preview:
Citation preview
John McCann, Carinna Parraman& Alessandro Rizzi
McCann Imaging, Belmont, MA, USA
Centre for Fine Print Research, University of the West of England, UK
Dipartimento di Informatica
48Edges and Gradients
in real 3-D color scenes
Color appearance can be analyzed either by an object's reflectance and scene illumination, or by edges and gradients.
• In one framework, appearance should correlate with reflectance, because humans might discount the spectra and the nonuniformity of illumination. • In the other, both reflectance and illumination make equal contributions to scene radiances. Edges generate large changes in appearance, while gradient are much less visible.
Experiments using painted blocks (3-D Mondrians) measured the appearance of objects with constant reflectance in complex real-world illumination.
We matched the appearances of identical surface reflectances in variable illumination.
Abstract
Matches of appearance correlate with the spatial configuration of
edges and gradients.
They do not correlate with reflectance and discounted illumination.
Summary
Experiment• Two identical sets of blocks [11 paints]
• Same room - same time
• Two different illuminations: HDR, LDR
• Compare the appearances of identical surface reflectances
Measurements• A. Magnitude estimate matches [Munsell Book]
• B. Painted reproduction of both LDR & HDR
• Rendering intent - match appearance
• Measure reflectance of watercolor painting
• A. Magnitude estimate matches [Munsell Book]
High Dynamic Range Illumination (HDR)
Average of 11 observers
Departures from “perfect constancy”are the signature of the
color constancy mechanism.
J. McCann, (2004) "Mechanism of color constancy," IS&T/SID 12th Color Imaging Conference: 29-36 358.
J. McCann, (2005) "Do humans discount the illuminant?,"HVEI, SPIE Proc, vol. 5666, 9-16.
LDR Painting Reflectance
0
20
40
60
80
100
400 500 600 700
Wavelength (nm)
Lig
htn
ess
(L*
)
30 LDR 32 LDR 33 LDR
18 LDR 9LDR
HDR Painting Reflectance
0
20
40
60
80
100
400 500 600 700Wavelength (nm)
Lig
htn
ess
(L*
)
30 HDR 32 HDR 33 HDR
18 HDR 9 LDR
LDR HDR
Appearance = Reflectance ?Planar LDR HDR
Yes Mostly Rarely Spatial, Cone
McCann JJ, McKee, SP.,& Taylor, T.
Vision Research, 16, 445–458, (1976).
<http://mccannimaging.com/Retinex/3-D_Mondrians.html>
Recommended