CIC24, November 7 – 11, 2016, San Diego, California
Large-gamut color and spectral display using sub-wavelength gratings
Peter Morovič†, Ján Morovič†, Francesco Aieta‡, Marco Fiorentino¶, Charles Santori§, David Fatal‡, †HP Inc, Spain, ‡LEIA 3D, ¶Hewlett Packard Labs, §Verily
© Copyright 2016 HP Inc.
Outline❖ Background
❖ Nanostructure gratings for displays
❖ Optimally selecting spectral primaries
❖ From RGB backlights
❖ From a white backlight
❖ The HANS imaging pipeline for displays
❖ Test setup & results
❖ Conclusions
© Copyright 2016 HP Inc.
Background❖ Displays are used ubiquitously in creating and consuming digital content
❖ Windows to remote events
❖ Previewing objects before production
❖ Range of their colors and spectra is very important
❖ Manufacturing: potential to replace or significantly reduce the production of prototypes
❖ Entertainment: experiences that are more vivid, life-like, intense, and convincing
❖ As a component of an object (e.g., e-ink smart-shoes): overall consistency of appearance
❖ Current displays: white backlight + absorptive filters / colored backlights
❖ Achieves limited gamut ← filters relatively broadband, incapable of approaching spectral locus
❖ Display with enhanced gamut → multiple narrowband backlights, but displays using more than 3/4 primaries have prohibitive cost & size
❖ Multiple narrow band light sources (e.g., lasers (Brazas and Kowarz, 2004), quantum dots (Kwak et al., 2012)) or notch filters, either absorptive or interference) → costly + limited resolution imposed by the manufacturing and assembly of filters
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Nanostructure gratings for displays
Spectral selection related to period of
grating.
Diffuser extends field of view.
Arbitrary number of sub-pixels can be defined, each with different selectivity.
Gratings can be tiled, manufactured using
large-scale lithography.
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Selecting filtered primaries: RGB backlights
Candidate LED spectra (normalized) Candidate LED spectra (absolute lumens)
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Selecting filtered primaries: 10 nm candidates
Candidate filtered primary spectra
25 primaries Choose 9 out of 25
2,042,975 combinations
Add threshold at 20 lumen: 22 primaries
497,420 combinations
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Selection of primaries
Optimal for spectral gamutVolume: 2.47x1020
Worst case: 7.43x1014
Optimal for CIELAB gamutVolume: 1.59x106
Worst case: 763White point: brightest 9–primary combination
Optimal for CIEXYZ gamutVolume: 1.97x108
Worst case: 7.20x103
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Optimized color gamutSpectral locus
HP DreamColor wide-gamut 3 LED
HP 12-ink printer
Optimally-selected9 narrow-band
primaries
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400 450 500 550 600 650 7000
10
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100
400 450 500 550 600 650 7000
10
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Filtering a single, white backlight
350 400 450 500 550 600 650 700 7500
0.1
0.2
0.3
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0.5
0.6
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0.8
0.9
1
Thorlabs Warm White LED 25 candidate primaries Gamut-maximizing choice of 9
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0 0.1 0.2 0.3 0.4 0.5 0.6
0.05
0.1
0.15
0.2
0.25
0.3
0.35
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0.55Spectral locus
sRGB
Optimally-selected9 narrow-band
primaries (from RGB)
Optimally-selected9 narrow-band
primaries (from W)
Optimized color gamut
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The HANS imaging pipeline for displays
Each pixel consists of NxN
sub-pixels.
Intensity can be controlled
continuously (e.g., via an LCD).
Static mask also possible → lower-
cost, static displays (e.g., point of sale, posters, …).
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The HANS imaging pipeline for displays❖ 9 sub-pixel primaries → 29=512 display primaries
❖ Color → find combination of 512 primaries that convexly combine to it
❖ Traverse all polyhedra formed by 512 primaries’ colorimetries
❖ Select one enclosing polyhedron (e.g., tetrahedron)
❖ Barycentric coordinates of enclosing polyhedron are convex weights with which corresponding primaries need to be combined
❖ Use error diffusion, or PARAWACS (see paper at end of this session) to spatially distribute
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Test setupSEM micrograph
of test sample
Backlight Grating
TSR Displayed test patches
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Results
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Measured patches
9 pr
imar
ies
2 pa
irsbacklight
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Gamut & additivity
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Conclusions❖ These are first, proof-of-concept results done under prototype
conditions
❖ Measurements show clear signal that grating color filters provide primaries from white backlight that significantly exceed the standard, sRGB gamut
❖ Greens close to the HP DreamColor display with RGB backlights
❖ Brightness and energy efficiency are expect it to be relatively low in this configuration
❖ We only use light diffracted vertically
❖ More efficiency can be achieved using LCD shutter to modulate light diffracted at other angles.
❖ Combination of nanotechnology and advanced color analysis techniques offers new platform for high quality and scalable large color gamut displays
© Copyright 2016 HP Inc.