Digital Signal Processing Reference
In-Depth Information
In the design procedures shown in Section 3, here we choose
σ
=
30
for di-
dim 2 2
×
mension
22
, due to the reason
that the typical values for PSNR in lossy image compression are above 30 dB and
acceptable values for wireless transmission quality loss are about 20 dB to 25 dB. The
experimental results shown in Table 1 are illustrated in Fig. 3, together with the
choice of the thresholds
,
σ
=
25
for dimension
44
and
σ
=
25
×
×
dim 4 4
×
m
σ
σ
and
.
dim
m
, we can select the proper codebooks
for the original image. In the case of image Lena, we choose the hierarchical code-
books with size
With the reasonable threshold
σ
and
σ
dim
m
. Then
by executing Step 3 in Section 3, we can get the structure (edge and adjacent) regions
denoted by black and blue sub-blocks and other smooth background regions by green
blocks, as shown in Fig. 4. Since the structure regions contain high-detail information
of the image which are very important features for perceptual quality, we select code-
book with dimension
2×
to code this type of region. For low-detail smooth back-
ground regions, another codebook with dimension
4×
is chosen. By choosing the
codebooks with different dimensions for different regions, we can obtain the recon-
structed image by our hierarchical clustering VQ framework in Fig. 5. The specifica-
tions of the reconstructed image are
PSNR
M
=
32
and dimensions being respectively
44
and
22
×
×
=
29.40
,
SSIM
=
0.81
and
bpp
=
0.68
.
Fig. 3.
The experimental results shown in Table 1 together with the choice of the thresholds
σ
σ
and
σ
. The upper black line is the threshold
and the lower is
σ
dim
dim
m
m
Fig. 4.
Hierarchical VQ blocks (black and blue are structure region of the image and green are
normal smooth region)
