Digital Signal Processing Reference
In-Depth Information
Fig. 14-5 is enough. For example such images can be utilized well for a
mobile phone. Then at the receiver side we can reconstruct the images whose
picture quality is like those of Fig. 14-5(a) and 14-5(b) when we can get only
the DWT approximation. This means that the data to be sent is just 1/4 of the
original. The DWT approximation can be compressed and coded through an
ordinary JPEG or JPEG2000 method. Hence, for example, if the JPEG
method gives us 4/5 reductions of the image data then the needed data to be
transmitted is only 1/20 of the whole image data.
3.3
Image Compression
Many DWT coefficients are nearly zero but actually not equal to zero.
Consequently we had better take the above corresponding difference instead
of zero values. Then taking a threshold value processing the bit rate
reduction can be achieved:
where,
and is DWT detail, is the estimate of
D(i,j)
is the
corresponding difference described in the former section, and is the error
of from the true value has a zero mean and small
variance. Since we can create
D(i, j)
from the DWT approximation at the
receiver side we can reconstruct the image if we obtain Then
must be transmitted to the receiver side. Consequently only fewer bits are
needed to transmit because
has small variance with zero mean.
