Visual and technical quality control for high definition television

16/10/08

Tom Beckers

Wim Ermens

Visual and Visual and technicaltechnical qualityquality controlcontrolforfor high high definitiondefinition televisiontelevision

VRT-medialab: onderzoek en innovatie2

Overview

Video quality control in a filebased world

Impact of HDTV emergence on quality control

Video quality evaluation

Production chain simulation

Broadcast chain simulation



AudioVisual Quality Control

! Audio

! Video

! Interaction between audio and video : e.g. lipsync

File based AV Quality Control

! Part of an automated or manual workflow

– Diagnose

– Repair / Redo




Technical quality control

! Container

! Metadata

! Interaction between container, audio and video : e.g. duration of tracks

File based technical quality control

! Part of an automated or manual workflow

! Application specifications




Automated QC



MXF analysis & application

specification validation

MXF

fileMXF

analysis

IRT MXF

Analyzer

Ardendo

CheckMXF

Application

Specification

Validator

MXF

analysis

report

Archive

Play-out

Production

Contribution

D-10 (APP)DV-25 (News)Application Specs HD



Application specification

validation report


720p !

1080i

1080i !

720p

720p !

1080i

1080i !

720p

1080p !

1080i

1080i !

1080p

720p !

1080p

1080p !

720p

Safeguarding audiovisual quality

! Maintaining quality throughout the production chain

– Choose material as close to source as possible

– prevent unneeded multi-generation

– Try to produce with the shortest/’most apt’ chain

– Prevent unneeded multi-generation

– Prevent transcoding

– Check quality

! Carefully design the production chain

– Choose the right codecs

– Choose the right equipment

Black Box

(in production/broadcast

chain)

720p

1080i

720p

1080i




Proliferation of raster formats

HD TVSD TV

720p50 1080i50

1080p25

1080p50

PAL

576i50



Proliferation of codecs

YUV

RGB4:2:0 / 4:1:1

4:2:24:4:4

HDCAM

HDCAM-SRDVCProHD

XDCAM HD

XDCAM HD422

HDV

AVCHDAVC-Intra

JPEG2K

DNxHD

ProRes Dirac

SVC

50 Mbps

100Mbps180Mbps

440Mbps

8 bit sampling

10 bit sampling



Viewer quality expectation

! Consumer expects ROI from flat panel investment

! Depends on content type (drama, news, sports, soap)

What codec to choose?

! Picture quality

! Bit rate

! Performance

! Support

! Scalability

! quality evaluation needed





Video sequence used for testing

(source EBU) :

! High quality source material

! 10-bit YCBCR samples

! Chroma subsampling 4:2:2

! HD-SDI compatible

! 720p50


Note on viewing conditions

Expert evaluation :

! Class 1 reference monitor @ 1H, 3H

! High quality consumer device (FullHD, Plasma) @ 1H, 3H

Present demo setup

! Overhead projector (internal processing?)

! Not sufficiently dark room

! Sub ideal circumstances

Interested parties : ask for demo in better circumstances...


Video quality in production chain

Simulation chain

without

pixelshift with

pixelshift (+2H, +6V)

Camera

encoding

Post production encoding

(4 generations)



Codecs tested :

! Camera : AVC-I, DVCProHD, XDCAM HD422

! PostProduction : DNxHD, AVC-I, DVCProHD, XDCAM HD422

Codec properties

LongGOP

(n=12 @ 720p)

I frames only

I frames only

I frames only

GOP

None84:2:2115DNxHD

None84:2:250XDCAM

HD422

3:4 horizontal :

960 luma samples/line

84:2:2100DVCProHD

None104:2:2100AVC-I

Spatial subsamplingSample

size

(bits)

Chroma

subsampling

Bitrate

(Mbps)

Codec



Test setup

Sony PDW-HD1500*

XDCAM HD422

Panasonic AJ-HPM110**

DVCProHD

AVC-I

Avid Airspeed + DNXchange

DNxHD

* test model provided by Sony Belgium** test model provided by Panasonic Belgium



Test setup

Uncompr.

source

Gen 0

(Cam)

Gen 4

(PP4)

Gen 1

(PP1)

Gen 2

(PP2)

Gen 3

(PP3)

Gen 3

shifted

Encode Decode

HD-SDI HD-SDI

Uncompressed YCbCr storage

HD-SDI ingest & playout



Evaluation methods :

! Objective tests

! Subjective tests

! Automated subjective tests

! Expert viewing



Objective tests : PSNR, SSIM, ...

!!"

=

"

=

"=1

0

1

0

2),(),(

1 m

i

n

j

frame jiIjiRmn

MSE )(log20 10

frame

Rframe

MSE

MAXPSNR !=

Reference Impaired Squared difference



Objective tests : PSNR, SSIM, ...

3 resultsets per sequence (Y, Cb,

Cr)

unsensitive to grouping of pixel

differences

objective

reproducible

automated test

DisadvantagesAdvantages



Subjective tests : DSCQS, TSCES, ...



(D)MOS scores

Upper anchor

Source material

Material to be

evaluated

Lower anchor

Worst case



Subjective tests :

DSCQS, TSCES, ...

difficult to test many sequences

timeconsuming to setup

difficult to get sufficient statistics

worst case reference definition

closest to real life experience




Automated subjective tests : Tektronix PQA-500, Opticom PEVQ Analyzer, ...

! Aims to provide (D)MOS score

! Simulate :

– Monitor setup and characteristics

– Viewing setup and conditions

– Viewer setup and characterisics

– Human visual system (= tricky)

good correlation to subjective test

results to be proven

typically slower than objective tests

automated test

closer correlation to subjective test

results than PSNR

no worst case reference mandatory




Expert viewing

! Aim :

– Visually evaluate video quality

– Determine typical artefacts

– Compare source with test material

– Compare test material with other test material

! Method :

– Create splitscreen images

– Evaluate on (reference) monitor

– Create ranking from intercomparison



Expert viewing (“The proof of the pudding is in the eating”)



Uncompressed vs Compressed video material



Compressed vs Compressed video material


Video quality due to de-interlacing

De-interlacing: difficult to perform

Good quality converters exist (price!)720p - DNxHD (Gen0) 1080i - DNxHD (Gen0) – de-interlace – 720p

source de-interlaced


Video quality in distribution chain


Distribution encoder

Distribution encoder = device that compresses the broadcaster’s signal into

a format suitable for transmission/distribution

Codecs: MPEG-2 or MPEG-4 H.264 (tested)

Interfaces: HD-SDI " ASI

Typical bitrate in/out:

! From 50-200 Mbit/s " 10 Mbit/s (or less)

Parameters:

! Encoding delay

! Encoder bit-rate

! Profile/Noise reduction/GOP size/…


Distribution encoder: bit-rate

Which bit-rate to choose?

! Distribution channel ‘defines’ available bit-rate

! MPEG-4 does a fine job

! Motion in video is important

Uncom

pre

ssed

AV

C/D

NxH

D –

16M

bit/s

H.2

64

AV

C/D

NxH

D –

10M

bit/s

H.2

64

AV

C/D

NxH

D –

8M

bit/s

H.2

64


Distribution encoder and production codec

Uncompressed HD ~ 1 500 Mbit/s

Production bitrate ~ 100 Mbit/s

Distribution encoder ~ 10 Mbit/s

Do we actually see the influence of the production codec?

AVC/AVC + 8 Mbit/s H.264 DVC/DVC + 8 Mbit/s H.264


Distribution: the end of the chain

Receiver (set-top-box)

! Interlacing – de-interlacing

! Scaling

Television

! A lot of choice

! De-interlace

! Scale

! Process (sharpen – noise reduction)

Make sure there’s no unnecessary signal conversion

Date post:	29-Nov-2014
Category:	Technology
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Visual and technical quality control for high definition television

Technology