Digital Signal Processing Reference
In-Depth Information
Figure 5.8.
5.3 Video Scaling for Different Aspect Ratios
This topic can be confusing, so we will limit the discussion to
three common aspect ratios. We will focus on converting every-
thing to the nearly ubiquitous 16:9 aspect ratio found in today's
HDTVs.
Aspect ratio is essentially the width of a video frame divided by
its height
both expressed in one unit. The easiest way to
understand this is to use Excel and consider each cell as one unit.
If you highlight four cells in the horizontal direction and three in
the vertical direction you get the infamous 4:3 aspect ratio. This
was, and is, the aspect ratio of standard TV
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an artefact which
gives us the annoying black bars on our regular HDTVs. Of course,
you can highlight 12 cells in the horizontal direction and nine in
the vertical direction and still get the same aspect ratio i.e. 12:9
or 4:3.
All HDTVs have an aspect ratio of 16:9. You can reproduce this
in Excel by highlighting 16 cells in the horizontal direction and
nine cells in the vertical direction.
Cinematic film, on the other hand, uses an aspect ratio of
1.85:1 (amongst others, but this is common). To replicate this in
our Excel example, this ratio translates to 16.65:9.
Figure 5.9
shows these different aspect ratios.
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