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Aspect Ratio pt2 (widescreen content)


In the first part of this series we looked at standard 4:3 content and saw how the relationship between pixel aspect ratio and dimensions go together to define the shape of the frame. In this article we will look at widescreen content and examine a range of methods for producing and displaying widescreen content.

Widescreen content is becoming more and more popular, not only in cinema and broadcast production but in live event video too. There are many different aspect ratios in use across these disciplines which makes things more complex than perhaps they need be. For the sake of simplicity we will look only at 16:9 widescreen as this is the most popular of the wide aspect ratios and is the ratio that the majority of plasma and LCD screens are available in.

16:9 content comes in three basic flavors

  • Letterbox
  • Anamorphic
  • True 16:9

Letterbox content is normal 4:3 video which has black bars rendered across the top and bottom to mask off the central 16:9 display area. PAL video of this type has a frame size of 768x576 or 720x576, however the active video area is considerably lower resolution due to so much of the frame being masked off.

Letterboxed widescreen has the advantage that it can be displayed on regular 4:3 displays and mixed with normal vision mixers - all playback systems can deal with letter boxed widescreen as it is effectively the same as 4:3 content.

The majority of 16:9 displays (eg plasma and LCD screens) can be set to correctly crop the black bars from the top and bottom of the content so the display shows the active content area full screen

Anamorphic widscreen uses a 720x576 frame size with rectangular pixels - all of the pixels are used to display video content and it is thus significantly higher resolution than letterboxed video. When viewed at its native pixel dimension the content appears to be squashed - however when it is correctly displayed on a 16:9 display the content is stretched back out to the correct shape.

Anamorphic widescreen is easily displayed on all 16:9 displays and many modern 4:3 displays can be switched into a widescreen mode to correctly display anamorphic content. Anamorphic content can be mixed with regular 4:3 video mixers although you should be aware that the final output will be stretched out on the displays so any shapes generated by the vision mixer will end up being distorted (eg circle wipes will become oval)

Square Pixel 16:9 content uses square pixels commonly at 1024x576 (PAL+), 1280x720 (HDTV720)and 1920x1080(HDTV1080) These frame sizes are higher resolution than letterbox or anamorphic widescreen. Currently it is only really possible to playback Square Pixel 16:9 content from computer sources. These sources can be mixed with HD mixers such as the Grass Valley indigo and Edirol V440.



© Tom Bassford 2005-2006