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Unformatted text preview: ld use as model a Poisson distribution
with λ = 10/4 = 2.5 events/interval. 19.05.2009 Dr. Pierre Elbischger - MIP1/ISAP'SS09 k
36 Signal-to-noise ratio (SNR)
The SNR is a ratio between a signal
that contains meaningful
information and noise that is also
present in the signal and obscures
the meaningful information.
Because many signals have a very
wide dynamic range, SNRs are
usually expressed in terms of the
logarithmic decibel scale. Ps...
Pn... 19.05.2009 signal power noise power Dr. Pierre Elbischger - MIP1/ISAP'SS09 37 Signal-to-noise ratio (SNR) – Quantization Noise E11 sine wave sawtooth signal The error of the sine wave
is approximately uniformly
Signal power of a sine wave with amplitude A Quantization error
Assuming a uniform distribution of input signal values, the quantization noise is a uniformlydistributed random signal with a peak-to-peak amplitude of one quantization level,
The equidistant quantization step for a n-bit resolution is given by
The resulting quantization error is uniformly distributed with
and its power corresponds to the variance of the distribution 19.05.2009 Dr. Pierre Elbischger - MIP1/ISAP'SS09 38 Contrast in images
An object is visible in an image because it has a different brightness than its
The human eye can detect a minimum contrast c of about 0.5 to 5%, depending on
the observation conditions. 100% contrast is the difference between pure black and
pure white. In other words, humans can distinguish about 20 to 200 shades of gray
between the blackest black and the whitest white c = 0 pure black
c = 1 pure white Squares with diffeent contrast to the background (c is given in percent)
19.05.2009 Dr. Pierre Elbischger - MIP1/ISAP'SS09 39 SNR/CNR in images
An object is visible in an image only if its contrast is large enough to overcome the
random image noise. In general, trouble begins when the SNR falls below about 1.0.
Sometimes the signal
power in the SNR
calculation is replaced by
the contrast c of the
image resulting in the socal...
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- Spring '09