SC 12
SC 12
SC 12
of intervals
– Each interval is represented by a distinct codeword
Decoder mapping
reconstruct value
Components of a Quantizer
1. Encoder mapping: Divides the range of values that
the source generates into a number of intervals.
Each interval is then mapped to a codeword.
Codes
Variable-length coding
If li is the length of the codeword corresponding to the output yi,
and the probability of occurrence of yi is:
Simplest Quantizer
All intervals are of the same size say ,
2bits/pixel 1bit/pixel
The lower rate images are darker than the original, and the lowest-rate
reconstructions are the darkest.
The reason for for this is that the quantization process usually results in
scaling down of the dynamic range of the input.
For example, in the 1-bit-per-pixel reproduction, the highest value is 196
as opposed to 255 for the original image.
As higher gray values represent lighter shades, there is a corresponding
darkening of the reconstruction.
The other thing to notice in the low rate reconstruction is that wherever
there were smooth changes in gray values, there are now abrupt
transitions. This is especially evident in the face and neck area. This is
because a range of values is being mapped to the same value.
Uniform Quantization of Uniformly
Distributed Source
Summary:
If the distortion constraint is given as D*, then step size
can be calculated directly, since
2
D* =
12
M = (xmax – xmin)/