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Aspect Ratio andActive Format Description

How do we make it all fit?

Gerry FieldAmerican Public Television

St. Paul Public Television Quality Workshop - July 8-9, 2010

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Aspect Ratio Television Aspect Ratio Defined:

Picture frame: Ratio of image width to image height.

Not directly tied to resolution. HD Screens are typically 16:9. SD Screens are both 4:3 and 16:9. Programming is varied.

16:9, 4:3, 15:9, 14:9, 1.85:1, 2.39:1 etc.Mixed aspect ratio programs

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How do we make it all fit?

We must deal with two display sizes 16:9 and 4:3.

16:9 sets have over 50% household penetration.

Number of TV sets in the average U.S. household: 2.86.

U.S. homes with three or more TV sets: 54%

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How do we make it all fit?

There are two programming sizes 16:9 and 4:3.

Treat all widescreen as 16:9 unless we wish to crop other formats

Upconversion, Downconversion

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4:3 Image in a 4:3 Display

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16:9 Image in a 16:9 Display

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But…How do we make it all fit?

4:3 upconverted to 16:9Fills the height of the 16:9 frame but leaves blank “pillar boxes” on the sides.

Not a real problem if original quality is high.

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4:3 Image in a 16:9 Frame

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But…How do we make it all fit?

16:9 downconverted to 4:3

Fills the width of a 4:3 frame but leaves blank spaces on top and bottom.

“Letterboxed”

Not perfect for 4:3 but may be acceptable.

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16:9 Image “Letterboxed” in 4:3 Frame

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But…How do we make it all fit?

16:9 can also be “Center Cut”

Downconverted to 4:3.

This fills the height and width of a 4:3 frame but omits material on the left and right of the original image.

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16:9 Image

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16:9 Center Cut in 4:3 Frame

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However…..

Center Cut is only feasible if all active elements and graphics are maintained in the 4:3 center of the 16:9 image.

“Center Cut Safe” – Action and Titles

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16:9 Image in a 16:9 Display

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16:9 Image center cut to 4:3

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Worst Case 4x3 Letterbox up converted to 16:9

Then down converted using a 16:9 to 4:3 down converter.

“Postage Stamp”.

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16:9 Image in a 4:3 Display

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Up Converted to 16:9 as 4:3

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Down converted 4:3 Letterbox

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What is the proper way to treat this? It depends. Commercial Networks Up Convert 4:3 with

side panels. Down Convert 16:9 by Center Cut.

PBS Stations Up Convert primarily 4:3 with side panels and Down Convert by Center Cutting or Letterboxing.

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Anamorphic Commonly defines 16:9 “squashed” into 4:3

(Can also apply to 4:3 “stretched” to 16:9)

Used as a distribution techniqueo Most common is SD widescreen on D-Beta

Must be properly handled prior to emission If not, viewer sees “squashed” picture

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Full Screen 16:9

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Anamorphic 4:3

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Anamorphico Anamorphic or 16:9 SD programming may be

upconverted to 16:9 HD and distributed (at a bandwidth cost).

o Alternatively, 16:9 SD can be distributed with MPEG2 encoder flag set to 16:9.

o 16:9 SD included in ATSC A/53 standard.o SD 16:9 can co-exist with SD 4:3

o Member station IRD will output correct format as desired.

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Source SD 16:9

Sencore IRDMRD3187

16:9 HD or 16:9 SD

4:3 SD Center Cut

4:3, 16:9 Letterbox SD

If the MPEG2 flag is set to 16:9 at the MPEG2Encoder, the Sencore IRD will properly recognizeThe format and provide properly formatted video

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Down Converting

Some stations and channels are still SD only.

50 % of our viewers are still SD.

Most HD households still have 2nd and 3rd SD sets.

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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.

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Active Format Description - AFD

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

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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)

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

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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

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

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

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Consumer Issues

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Consumer Issueso Broadcasters cannot rely on consumers to

maintain aspect.

o AFD is not widely implemented on consumer devices.

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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.

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Questions? / Comments