Aspect Ratio and
Active Format Description
How do we make it all fit?
Gerry Field
American Public Television
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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 16:9
Fills 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 technique
o 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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Anamorphic
o
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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If the MPEG2 flag is set to 16:9 at the MPEG2
Encoder, the Sencore IRD will properly recognize
The format and provide properly formatted video
16:9 HD or 16:9 SD
Sencore IRD
MRD3187
Source SD 16:9
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4:3 SD Center Cut
4:3, 16:9 Letterbox SD
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
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In a 16:9 coded frame
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AFD = ‘1001’ (Full 4:3 / Pillarbox)
In a 4:3 coded frame
In a 16:9 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
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In a 16:9 coded frame
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AFD = ‘1111’ (Center Cuts)
In a 4:3 coded frame
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In a 16:9 coded frame
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Consumer Issues
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Consumer Issues
o
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
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