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Aspect Ratio and
Active Format Description
How do we make it all fit?
San Francisco Public Television Quality Workshop
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Aspect Ratio
 Television Aspect Ratio Defined:
Ratio of the width of an image to its height.
 HD Screens are 16:9.
 SD Screens are 4:3.
 Programming is ????.
 16:9, 4:3, 15:9, 14:9, 1.85:1, 2.39:1 etc.
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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.
 Percentage of 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 side crop other formats such as 15:9, 14:9,
1.85:1 2.39:1 etc.
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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 SD up converted to HD 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 HD Down Converted 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 HD can also be “Center Cut” Down
Converted 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.
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16:9 Image in a 16:9 Display
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16:9 Image Center cut Artifacting
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Worst Case
 Letterbox up converted to 16:9 as a 4:3.
 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 do this?
 There is no incorrect method.
 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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Full Screen 16:9
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Anamorphic 4:3
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Anamorphic

Full 16:9 “squashed” into a 4:3 frame.
 Unacceptable method of distributing HD material.
 Unacceptable as a distribution format.
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Anamorphic
 Anamorphic programming must be up converted to 16:9 HD then distributed.
 Distributor up converts once as opposed to stations each having to deal with an additional format.
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Down Converting

We don’t have to, ATSC is 16X9 HD !
 Some stations are still SD only.
 50 % of our viewers are still SD.
 Most HD households still have 2 nd and 3 rd 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 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.
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AFD Codes
 There are 16 AFD Codes.
 Realistically only four will be used.




1000 – Full Frame into 16:9 Letterbox.
1001 – 16:9 Center Cut into 4:3 Pillarbox.
1010 – 16:9 Into 4:3 Protected Letterbox
1111 –16:9 image with alternate 4:3 center
 14:9, 15:9, 2.35 etc. treat as 16:9.
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1000 – Full Frame into 16:9
Letterbox
Letter-box 16:9 into 4:3 scan
As the coded frame
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1001 – 16:9 Center Cut into 4:3
Pillar-box
Center cut-out 4:3 from
16:9 4:3 (center)
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1010 – 16:9 Into 4:3 Protected
Letterbox
Letter-box 16:9 into 4:3 scan 16:9 (center)
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1111 –16:9 image with alternate
4:3 center
16:9
(with shoot & protect 4:3 centre)
Centre cut-out 4:3 from
16:9
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Consumer Issues
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Consumer Issues
 Broadcasters cannot rely on consumers to maintain aspect.
 AFD is not widely implemented on consumer devices.
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So What do we do?
 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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