Q G WGBH Public Television Quality Workshop 1 Aspect Ratio and Active Format Description Gerry Field...
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Transcript of Q G WGBH Public Television Quality Workshop 1 Aspect Ratio and Active Format Description Gerry Field...
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
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What Happens Downstream?
4:3 Channel Letterboxed 16:9Typical for Multicast or Cable
16:9 Home Display Adds Pillars
Results in “Breadbox”
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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
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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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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”
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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
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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
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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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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
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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. Consider SD Widescreen distribution & channels
QG WGBH Public Television Quality Workshop22
Aspect Ratioand
Active Format Description
Gerry FieldAmerican Public Television