Digital Signal Processing Reference
In-Depth Information
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4:3 Aspect Ratio
Old Analog TVs
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16:9 Aspect Ratio
New HDTVs
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16.65:9 OR 1.85:1 Aspect Ratio
Commonly Used for Films
Figure 5.9.
The problem is fitting the 4:3 and the cinematic film aspect
ratio onto our HDTV. The simplest way is to take the 4:3 rectangle
and fit it on the 16:9 rectangle. When you try this you can
immediately understand why we see those black bars on the side.
Similarly, when you watch a Blu-ray DVD that is supposed to be
HD, you still get bars on the top and bottom. This is because the
Blu-ray movie was recorded with the aspect ratio of 1.85:1.
Figure 5.10
shows how the black bars appear when we try and fit
a different aspect ratio on regular HDTV screen.
The reason these aspect ratios are brought up here is that
you can immediately see one of the major uses for video
scaling. Most HDTVs have a scaling function which will change
the aspect ratio, but most of them employ simplistic scaling
algorithms
e
nearest neighbor or bilinear
e
and so the resul-
tant image is not very good.
