1. WGBH Public Television Quality Workshop
Aspect Ratio and Active Format Description Gerry Field American Public Television
WGBH Public Television Quality Workshop

2. WGBH Public Television Quality Workshop
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
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3. WGBH Public Television Quality Workshop
It’s Simple
Source Program Channel Viewer
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4. WGBH Public Television Quality Workshop
4:3 Image - 4:3 Frame
4:3 Image - 16:9 Frame
16:9 Image - 16:9 Frame
16:9 Image - 4:3 Frame
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5. What Happens Downstream?
4:3 Channel
Letterboxed 16:9
Typical for Multicast or Cable
16:9 Home Display
Adds Pillars
Results in “Breadbox”
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6. What Happens Downstream? Center Cut Alternative
16:9 Frame
Center Cut 4:3
One Alternative
4:3 Channel
Center Cut 4:3
Typical for Multicast or Cable
16:9 Home Display
Adds Pillars
No “Breadbox”
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7. 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
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8. Worst Case This Never Happens, Right?…
Letterboxed to 4:3
“Postage Stamp”
To a 16:9 Home Display
4:3 Frame
Letterboxed Content
Upconverted to 16:9
Typical Primary Channel
Downconverted for 4:3
Using Letterbox
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9. WGBH Public Television Quality Workshop
Anamorphic
Only 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
WGBH Public Television Quality Workshop

10. Speaking of SD & Widescreen
16:9 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
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11. WGBH Public Television Quality Workshop
Distributing SD Widescreen
Current workflow would need to be modified
Testing and vendor support required
Business requirements need to match
16:9 HD or 16:9 SD
Sencore IRD
MRD3187
4:3 SD Center Cut
Source SD 16:9
File or Anamorphic Tape
4:3 SD, 16:9 Letterbox
WGBH Public Television Quality Workshop

12. 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.
WGBH Public Television Quality Workshop

13. Active Format Description AFD WGBH Public Television Quality Workshop
May also be used for format conversion signaling in the post and pre-broadcast chain.
References:
- SMPTE ST :2009
- PBS TOS-1, 4.4
- PBS TOS-21, 4.3.7
- PBS Connect > Engineering/Compute >
Technical Reference Library
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14. WGBH Public Television Quality Workshop
AFD Codes
SMPTE ST :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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15. WGBH Public Television Quality Workshop
AFD = ‘1000’ (Full Frame)
In a 4:3 coded frame
In a 16:9 coded frame
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16. 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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17. WGBH Public Television Quality Workshop
AFD = ‘1010’ (Protected 16:9)
In a 4:3 coded frame
In a 16:9 coded frame
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18. WGBH Public Television Quality Workshop
AFD = ‘1111’ (Center Cuts)
In a 4:3 coded frame
In a 16:9 coded frame
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19. WGBH Public Television Quality Workshop
Consumer Issues
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20. WGBH Public Television Quality Workshop
Consumer Issues
Broadcasters cannot rely on consumers to maintain aspect.
AFD is not widely implemented on consumer devices.
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21. WGBH Public Television Quality Workshop
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
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22. WGBH Public Television Quality Workshop
Aspect Ratio and Active Format Description Gerry Field American Public Television
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