Databases Reference
In-Depth Information
F I GU R E 18 . 18
An example of quadtree partitioning.
and
h
j
are the largest indicate the row and column for
which there is maximum difference between two halves of the block. Depending on whether
|
v
i
|
The values of
i
and
j
for which
|
v
i
|
or
h
j
is larger, we can divide the rectangle either vertically or horizontally.
Finally, partitioning does not have to be rectangular, or even regular. People have experi-
mented with triangle partitions as well as irregular-shaped partitions [
251
].
The fractal approach is a novel way of looking at image compression. At present the
quality of the reconstructions using the fractal approach is about the same as the quality of the
reconstruction using the DCT approach employed in JPEG. However, the fractal technique is
relatively new, and further research may bring significant improvements. The fractal approach
has one significant advantage: decoding is simple and fast. This makes it especially useful
in applications where compression is performed once and decompression is performed many
times.
18.7 Summary
We have looked at two very different ways of using the analysis/synthesis approach. In speech
coding the approach works because of the availability of a mathematical model for the speech
generation process. We have seen how this model can be used in a number of different
ways, depending on the constraints of the problem. Where the primary objective is to achieve
intelligible communication at the lowest rate possible, the LPC algorithm provides a very
nice solution. If we also want the quality of the speech to be high, CELP and the different
sinusoidal techniques provide higher quality at the cost of more complexity and processing
delay. If delay also needs to be kept below a threshold, one particular solution is the low-delay
CELP algorithm in the G.728 recommendation. With the arrival of the internet the constraints
