Databases Reference
In-Depth Information
T A B L E 10 . 9
Initial codebook for Problem 3.
1
1
1
2
1
0
.
5
0.5
1
0.5
0
.
5
1.5
1
2
5
3
3
(b)
Modify the program so that the empty cell vector is replaced with a vector from
the quantization region with the largest distortion. Comment on any changes in
the distortion (or lack of change). Is the final codebook different from the one you
obtained earlier?
(c)
Modify the program so that whenever an empty cell problem arises, a two-level
quantizer is designed for the quantization region with the largest number of output
points. Comment on any differences in the codebook and distortion from the previous
two cases.
4.
Generate a 16-dimensional codebook of size 64 for the Sena image. Construct the vector
as a 4
1 block of pixels. Comment
on the differences in the mean squared errors and the quality of the reconstructed images.
You can use the program
trvqsp_img
to obtain the codebooks.
5.
In Example
10.6.1
we designed a 60-level two-dimensional quantizer by taking the two-
dimensional representation of an 8-level scalar quantizer, removing 12 output points
from the 64 output points, and adding 8 points in other locations. Assume the input is
Laplacian with zero mean and unit variance, and
×
4 block of pixels, an 8
×
2 block of pixels, and a 16
×
=
0
.
7309.
(a)
Calculate the increase in the probability of overload by the removal of the 12 points
from the original 64.
(b)
Calculate the decrease in overload probability when we added the 8 new points to
the remaining 52 points.
6.
In this problem we will compare the performance of a 16-dimensional pyramid vector
quantizer and a 16-dimensional LBG vector quantizer for two different sources. In each
case the codebook for the pyramid vector quantizer consists of 272 elements:
32 vectors with 1 element equal to
±
, and the other 15 equal to zero, and
240 vectors with 2 elements equal to
±
and the other 14 equal to zero.
The value of
should be adjusted to give the best performance. The codebook for the
LBG vector quantizer will be obtained by using the program
trvqsp_img
on the source
output. You will have to modify
trvqsp_img
slightly to give you a codebook that is
not a power of two.
