TV DisplaysSystem Level Overview

Dec 6 2004

Prinyar Boon

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New Displays - Technologies

• New raft of new display technologies are now a commercial reality– LCD, LCOS, LCD-TFT, DMD, Plasma, LED,

OLED, SED, GLV….

• Each display technology has a unique set of fundamental characteristics

• Each Commercial Implementation also has its set of individual characteristics

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New Displays - New Opportunities

• New technologies present new business opportunities– D-Cinema– E-Cinema– Mobile: Plane, Car, Phone, PDA– E-Billboard– E-Commerce– Digital Photography– Electronic Proof [Print, Film]

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New Displays – New Problems

• Television - Today– Grade 1 CRT Monitor

• Television – Future– LCD, Plasma, DLP, SED, OLED?

• Film – Today– 48Hz projector; 4 perf 35mm Ansa-print

• Film – Future => D-Cinema– Reference projector

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Working Groups

• TV Broadcast– SMPTE I23 Display ad hoc group: Dave Bancroft

– EBU

• TV Domestic– UK: DTG Display working group: David Holliday

– Europe: EICTA

• Film D-Cinema– SMPTE DC28 Colorimetry ad hoc group: Glenn

Kennel

– ITU

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What does the Display do?• Integral to image rendering process• Electro-optical conversion transfer characteristic

[gamma]Linear light outputSystem rendering intent

• Implied display filterPartly defines output image contrast [+ Room]Upper bound on image resolution [H,V,T]May directly modify the image

• Determines image size and shape [aspect ratio and framing – crop/overscan]

• Determines Image Luminance levels• Determines Image Chromaticity

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What does the Environment do?

• Integral to rendering of the image– Limits image size and shape– Bounds viewing distance– Determines the required display peak

luminance [sunlight viewing >5000 nits]– Contrast contributions

• Limiting Contrast [room light + reflected light]• Psycho-visual effects

– Modifies image Chromaticity– Determinate of system ‘rendering intent’

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LENS

CAMERASTUDIO MONITOR

DOMESTIC DISPLAY

TV: Origins Studio

• Studio Reference Monitor defined as CRT…Alas:– Display Gamma ‘assumed’ [2.1 – 2.8?]– Channel coding Gamma not defined– Temporal characteristics - not defined– CRT is also part of the “display filter” - not defined

• Studio Reference viewing conditions defined– Defines required studio ‘rendering intent’

• Camera is adjusted to give wanted picture - ref. image– camera creates OUTPUT/DISPLAY referred data– Complex mixture of >4 gamma characteristics

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LENS

CAMERASTUDIO

MONITOR

DOMESTIC DISPLAY

TV: Origins Home

Home display type: CRT• Simple Transmission system [Analogue SD – part of

display filter]• Domestic gamma, temporal and display-filter

characteristics “benign”, by virtue of being a CRT display• Home viewing environment poorly defined

– rarely matches reference conditions– contains observable colours

• CE manufacturers do whatever they can to sell product– Home display adapted to CE view of the home

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TV Display Alliance - Broadcaster

• Broadcaster has Little or No control over domestic display characteristics

• Broadcaster had No control over domestic viewing environment

• Broadcaster can only control the image as created in the studio– The broadcaster can only define the ‘intent’ of

the data that is transmitted– The ‘intent’ is a function of reference display

and reference environment

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TV Display Alliance - CE

• CE manufacturer modifies the image for commercial gain– Domestic environment

– ‘Vibrant’ image, brighter, more saturated

– Modern [HD ready] matrix displays “sharper” than grade 1 CRT

• Highly reliant on the Broadcast image [intent] having defined characteristics– CE technology often pushed to limits of ‘just working’

– Particularly with early adopters or cost down

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LENS

CAMERASTUDIO MONITOR

DOMESTIC DISPLAY

TV: Today’s complications

• Move from 4:3 to 16:9– Mix of 4:3 and 16:9 reference [by genre]– Mix of 4:3 and 16:9 services [analogue/digital]– Mix of 4:3 and 16:9 display in the home

• Compressed Transmission– Mix of compression systems + PAL– Concatenated compression

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LENS

CAMERASTUDIO MONITOR

DOMESTIC DISPLAY

TV: The Future

• Studio and /or Domestic display type may not be CRT• SD and HD Services• CE display will have modified characteristics

– Bad for the Broadcaster [e.g. compression artefacts, visibility of noise]

• Reference image may change– Bad for CE manufacturers [Enhancement “tricks” make the picture

look worse]• CE Display may have Wide colour gamut [Digital

Photography]

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Dynamic Contrast

• Domestic CRT– Beam current limiting– Small area Light output say 450 cd/m2– Wide area say 120 cd/m2

• Plasma– Power limiting– Similar characteristic to domestic CRT

• Professional CRT Monitor – constant peak Luminance regardless of area

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Specular Highlight – Coding Range?

• Could formally re-define white code – by area– Medium/Large area

– Specular Highlight [small area]

• Large area code remains 235 [decimal 8 bit]– Camera ‘knee’ set for this code - defined

• Current headroom is now specified to be used for specular highlights– Camera [non linear] highlight compression used in this

code range

– Equipment includes soft clip for over-range

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Matrix “Native” Resolutions

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TV System Concatenated Scalers

• Studio Aspect Ratio Converter

• Studio Up/Down/cross Format converter

• Mpeg Encoder e.g. 720 to 540 H pixel

• Mpeg Decoder e.g. 540 to 720 H pixel

• STB and/or display Up/Down/Cross

• STB and/or display de-interlace [if needed]

• Display TV to ‘Native’ Format conversion

• Overscan

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TV Matrix Display Scalers• Matrix Display Usually Progressive

– Must De-interlace

• Resolution is fixed – rarely matches TV structure– Cannot Multiscan, Overscan, Aspect Ratio Convert as

per CRT monitor. MUST interpolate and filter– Will involve up or down conversion– Expansion ratio may be small

• Display Scaler – usually very cheap– Image spectrum may have been damaged by upstream

processing

• Display Scaler is in effect the DISPLAY FILTER

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Temporal Effects• LCD Sample and Hold

– No Wide Area Flicker [except backlight]– Noise is also ‘held’– Blur with Eye Tracking

• LCD Slow switching speed [Lag]• LCD Suppresses Line Twitter and Motion Judder• PWM systems – limited bit depth with motion

[single chip systems even worse]• Bright Plasma – some low level wide area flicker• Single chip displays – Sequential RGB “Rainbow”

effect• Display refresh may not be locked to video!

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Matrix Display Gamma• DMD, LCOS, LCD, LED, Plasma

– Modulate in linear Light– 8 bits gamma >> requires 12[ish] bits in linear light

• DMD, LED, Plasma – PWM– Digital definition of display “gamma” curve– May be bit limited [New Plasma 10 bits linear light]

– Bit depth limited PWM displays contouring in blacks– Spatiotemporal Dither – limited bit depth with motion

• LCOS, LCD– Mixed Analogue/Digital characteristic– Some LCD’s non monotonic!

• Some displays are non monotonic!

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D-Cinema Channel Coding Gamma

12 bit gamma 2.6

Barten HVS prediction

10 bit gamma 2.6

10 bit log (step.009)

12 bit log (step .0023)

Steps visible

Steps not visibleCinema operation range

Luminance, ft-L

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TV Gamma requirements

• What is the Ideal gamma curve?– If enough bits, then gamma is not required– Companding operation

• What is the ideal bit depth in:– Gamma pre-compensated space?– Linear Light?

• Dependent on Luminance levels• Barten Threshold

– Digital Cinema DC28 tests

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TV Gamma Evolution?

• CRT Gamma may not be optimum for TV light levels– Barten Threshold?

– New Research topic?

• Could specify– Channel coding gamma in reference environment

– Decoding characteristic of Reference Display in Reference environment

– Decoding characteristic of Reference Display in Reference domestic environment

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Things to do?• Specular Coding Range, Camera knee• Define Channel coding characteristic

– Research ideal curve• Define Reference display in one document+

– De-code curve– Temporal characteristics

• Display Filter– Where in the system?– Concatenated Scaling

• Advise to broadcasters• Select replacement technology for CRT + “fixit”

box

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TV Matrix Display – Size + Lumens

• Larger viewable area– Average UK CRT currently 28-32” diagonal– Flat panel typically 42” diagonal [32”- 65”]– Rear projection typ 50” diagonal [40” – 80”]– Front projection >72” horizontal

• Brighter– Modern Plasma - small area up to 1000cd/m2– Domestic CRT - small area 450cd/m2– LCD - wide area 450cd/m2

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However

• Room size is fixed– Viewing distance reduced [in picture heights]– Image appears bigger

• Screen is brighter– Colours appear more saturated– Image appears more ‘contrasty’

• Noise, Cross colour/Luminance, Twitter, Wide area Flicker - more visible

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TV Matrix Display - Contrast

• On/Off Contrast– Plasma 1000:1 to 3000:1– LCD 600:1 to 900:1– Single chip projector >2500:1– 3 chip projector 800:1 – 2200:1

• On/Off Contrast measure may not be a meaningful metric

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Contrast Measures• On/Off [Sequential] Contrast

– Display Measured in “perfect room”– Ignores display optics– Always gives the highest ratio

• ANSI Contrast [9 or 16 tile Black White Chequerboard]– Medium Area Measure– Includes Optical flare– 50% APL not ideal for Cinema/Film use

• Projection systems can use Screen measure• Limiting Contrast [Room]• Small Area Contrast [HF depth of modulation]

– Dominates display resolving power

• “Contrasty” Image– Creative/subjective contrast

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Cinema Contrast Comparison [Screen - Reflected]

675:1550:1600:1ANSI

(incident)

150:1150:1135:1ANSI

Contrast

1700:11100:13900:1Sequential

Contrast

DLP-2K

(M25)

DLP-1K

(M15)

Film

(Vision)

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Contrast or Contrasty?

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Contrast or Resolution?

• High contrast edge will appear sharper

• HDTV systems allow preservation of scene contrast in presence of high detail or texture

• Sharpness - Ability of the system to deliver high resolution, high contrast images

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TV Transfer Characteristic

• Overall Characteristic for TV:1.25 - Rendering Intent - Includes the display surround

• Studio has Dark surround, New CE displays have silver surround

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Surround Effect

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Black Recovery• Digital TV coding range

– ‘Nominal’ Black code 16 in Luma channel– Sub Nominal Black is allowed

• ‘Operating’ Black point– Function of reference display, environment and

observer

• Display cannot generate Sub Black• What is Ideal black cut off in RGB linear light

space?– Requires knowledge of the operating black point– Sub black clip

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PWM - Good, Bad, Ugly[LED Wall]

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Colorimetry• Light Valve displays may have de-saturated primaries –

increases optical efficiency• Display manufacturers can modify colour temperature• Increasing interest in Wide Gamut displays for Film work,

digital photography, print proof– GLV laser– >3 primary systems– LED backlight for LCD panels– LED light source for LCD projectors

• Narrow primary stimulus – more prone to viewer variablity• ITU-R BT.1361 backwards compatible with BT.709• Gamut Mapping/Limiting problem

– Non linear characteristics

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CRT [mesh] vs Film Gamut

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Does Any of this Matter?

• STEM images to demonstrate– Different projector types– Different gamma– Different white points

• Thanks to Matt Cowan [ETC], Ron Williams [Landmark Group]– Presented at SMPTE Pasadena 2004

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709 Color space “master data”

Master

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As appears on laser primaries

Master

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Higher display gamma

Master

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Lower display gamma

Master

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Warm color temperature

Master

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709 Color space “master data”

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As appears on laser primaries

Master

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Higher display gamma

Master

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Lower display gamma

Master

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Warm color temperature

Master

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Display Digital Interconnect• DVI: VESA originated – PC Graphics

Adapted for video8 bit RGB up to 1600 x 1200 x 60P [25-165Mhz

word clock – note: Variable clock]Standard on all modern PC Graphics cards and TFT5M no EQ, >20M with EQHDCP Copy protection optional

HDMI: CE centricHDCP MandatorySome chipsets limited to baseband TV rates

Video Format – EIA/CEA 861-BCoding Scheme – TMDS [Silicon Image]

Licensing issues

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RENDERREFERENCEPROJECTOR

SCREE NRGB PIXELSOF LIGHT

LE NS

CAMERA

FILM flow – Offline TV Future?

• Camera Captures Scene Referred Data– Large Latitude, Huge amount of information on the Negative

• DP Controls the “look” to help tell the story• Scene Referred Data is RENDERED to achieve the “look”

– Printer lights, bleach bypass [analogue film]

– Digital Grading [Digital Intermediate]

– Decoupling of the Scene from the display..NOT Television

• Rendering process is viewed on a reference projector/Env• Rendered Data [Print] is now Display/Output Referred