QG WGBH Public Television Quality Workshop1

Aspect Ratioand

Active Format Description

Gerry FieldAmerican Public Television

QG WGBH Public Television Quality Workshop2

Aspect Ratio Television Aspect Ratio Defined:

Picture frame: Ratio of image width to image height. Not directly tied to resolution

Historically, TV content and frame had been 4:3 Content is both 4:3 and 16:9.

16:9, 4:3, 15:9, 14:9, 1.85:1, 2.39:1, mixed aspect ratio TV frame is now 16:9 in > 50% households Millions of 4:3 receivers remain in use Channels are both 16:9 and 4:3

QG WGBH Public Television Quality Workshop

Source Program Channel Viewer

3

It’s Simple

QG WGBH Public Television Quality Workshop4

4:3 Image - 4:3 Frame

16:9 Image - 16:9 Frame

4:3 Image - 16:9 Frame

16:9 Image - 4:3 Frame

QG WGBH Public Television Quality Workshop5

What Happens Downstream?

4:3 Channel Letterboxed 16:9Typical for Multicast or Cable

16:9 Home Display Adds Pillars

Results in “Breadbox”

QG WGBH Public Television Quality Workshop6

What Happens Downstream?

Center Cut Alternative

4:3 Channel Center Cut 4:3

Typical for Multicast or Cable

16:9 Home Display Adds Pillars

No “Breadbox”

16:9 Frame Center Cut 4:3

One Alternative

QG WGBH Public Television Quality Workshop7

However…It Doesn’t Work For All Content

16:9 Frame Center Cut 4:3

NOT Center Cut Safe

4:3 Channel Center Cut 4:3

NOT Center Cut Safe

16:9 Home Display Center Cut 4:3

NOT Center Cut Safe

QG WGBH Public Television Quality Workshop8

Worst CaseThis Never Happens, Right?…

Upconverted to 16:9Typical Primary Channel

4:3 Frame Letterboxed Content

Downconverted for 4:3Using Letterbox

Letterboxed to 4:3

To a 16:9 Home Display

“Postage Stamp”

QG WGBH Public Television Quality Workshop9

AnamorphicOnly Use as a Distribution Technique

Not as a Broadcast Format

Most common is SD widescreen on D-Beta

Must be properly “stretched” prior to emission

If not, viewer sees “squashed” picture

Common practice is to upconvert to HD at a bitrate cost

QG WGBH Public Television Quality Workshop10

Speaking of SD & Widescreen16:9 is not limited to HD

16:9 SD is included in ATSC A/53 standard. and is regularly used in domestic and overseas markets

16:9 SD can be distributed if MPEG2 encoder flag is set to 16:9. SD 16:9 can co-exist with SD 4:3

QG WGBH Public Television Quality Workshop

Source SD 16:9File or Anamorphic Tape

Sencore IRDMRD3187

16:9 HD or 16:9 SD

4:3 SD Center Cut

4:3 SD, 16:9 Letterbox

Distributing SD WidescreenCurrent workflow would need to be modifiedTesting and vendor support requiredBusiness requirements need to match

QG WGBH Public Television Quality Workshop12

Active Format Description AFD

A four bit code to define the active and protected image area.

Intended to guide professional video equipment, consumer receivers and set-top boxes to optimize the displayed image.

Very few ATSC receivers and consumer decoders act on AFD.

QG WGBH Public Television Quality Workshop13

May also be used for format conversion signaling in the post and pre-broadcast chain.

References:- SMPTE ST 2016-1:2009- PBS TOS-1, 4.4- PBS TOS-21, 4.3.7- PBS Connect > Engineering/Compute >

Technical Reference Library

Active Format Description AFD

QG WGBH Public Television Quality Workshop14

AFD Codes SMPTE ST 2016-1:2009 defines 17 AFD Codes.

Four are in common use:

1000 – Full Frame 1001 – Full 4:3 / Pillarbox 1010 – Protected 16:9 1111 – Center Cuts

(14:9, 15:9, 2.35 etc. treated as 16:9)

QG WGBH Public Television Quality Workshop15

AFD = ‘1000’ (Full Frame)In a 4:3 coded frame In a 16:9 coded frame

QG WGBH Public Television Quality Workshop16

AFD = ‘1001’ (Full 4:3 / Pillarbox)

In a 16:9 coded frameIn a 4:3 coded frame

In a 4:3 coded frame, AFD code ‘1001’ represents the same image display as AFD code ‘1000’.

AFD code ‘1000’ is the preferred coding for a full frame 4:3 image

QG WGBH Public Television Quality Workshop17

AFD = ‘1010’ (Protected 16:9)In a 4:3 coded frame In a 16:9 coded frame

QG WGBH Public Television Quality Workshop18

AFD = ‘1111’ (Center Cuts)In a 4:3 coded frame In a 16:9 coded frame

QG WGBH Public Television Quality Workshop19

Consumer Issues

QG WGBH Public Television Quality Workshop20

Consumer Issueso Broadcasters cannot rely on consumers to

maintain aspect.

o AFD is not widely implemented on consumer devices.

QG WGBH Public Television Quality Workshop21

So What do we do? Educate. Implement AFD. Discuss with Cable and Satellite providers to

Implement AFD on their SD Down convert. Produce when appropriate 16X9 Center cut safe

material. If necessary up convert Letterbox to 16X9 Full

frame. Consider SD Widescreen distribution & channels

QG WGBH Public Television Quality Workshop22

Aspect Ratioand

Active Format Description

Gerry FieldAmerican Public Television