DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Magnitude frequency
response, relative
0.707
There are other definitions of bandwidth,
but this is the definition that
I recommend. In magnitude squared
response, the half-power point is at
0.5 on a linear scale.
Input
Output
1.0
HALF-POWER
(-3 dB)
0
0 Frequency, relative
BANDWIDTH
LIMITING
RESOLUTION
Figure 7.1 Magnitude frequency response of an electronic or optical system typically falls as
frequency increases. Bandwidth is measured at the half-power point (-3 dB), where response has
fallen to 0.707 of its value at a reference frequency (often zero frequency, or DC). Useful visible
detail is obtained from signal power beyond the half-power bandwidth, that is, at depths of
modulation less than 70.7%. I show limiting resolution, which might occur at about 10% response.
Bandwidth characterizes the range of frequencies that
a system can capture, record, process, or transmit. Halfpower
bandwidth (also known as 3 dB bandwidth) is
specified or measured where signal magnitude has
fallen 3 dB – that is, to the fraction 0.707 – from its
value at a reference frequency (often zero frequency, or
DC). Useful visual information is typically available at
frequencies higher than the bandwidth. In image
science, limiting resolution is determined visually.
The maximum rate at which an analog or digital electronic
signal can change state – in an imaging system,
between black and white – is limited by frequency
response, and is therefore characterized by bandwidth.
66 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES