large-gamut color and spectral display using sub-wavelength gratings

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


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


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.


Selecting filtered primaries: RGB backlights

Candidate LED spectra (normalized) Candidate LED spectra (absolute lumens)


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


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


Optimized color gamutSpectral locus

HP DreamColor wide-gamut 3 LED

HP 12-ink printer

Optimally-selected9 narrow-band

primaries


400 450 500 550 600 650 7000

10

20

30

40

50

60

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90

100

400 450 500 550 600 650 7000

10

20

30

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50

60

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100

Filtering a single, white backlight

350 400 450 500 550 600 650 700 7500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Thorlabs Warm White LED 25 candidate primaries Gamut-maximizing choice of 9


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

0.4

0.45

0.5

0.55Spectral locus

sRGB


primaries (from RGB)


primaries (from W)

Optimized color gamut


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, …).


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


Test setupSEM micrograph

of test sample

Backlight Grating

TSR Displayed test patches


Results


Measured patches

9 pr

imar

ies

2 pa

irsbacklight


Gamut & additivity


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

large-gamut color and spectral display using sub-wavelength gratings

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