Image Processing Reference

In-Depth Information

Table 1

Recommended JPEG 2000 Frequency (
s
) Weighting for 400 dpi (
s
= 1 is the Lowest Fre-

quency Wavelet Plane)

s
Horizontal Vertical Diagonal

1

1

1

1

2

1

1

0.731668

3

0.564344

0.564344 0.285968

4

0.179609

0.179609 0.043903

5

0.014774

0.014774 0.000573

3 Perceptual quantization

3.1 Contrast Band-Pass Filtering

an observer at a distance
d
just by modeling the perceptual chromatic induction processes of

the HVS. That is, given an image
I
and an observation distance
d
, CBPF obtains an estimation

of the perceptual image
I
ρ
that the observer perceives when observing
I
at distance
d
. CBPF is

based on just three important stimulus properties: spatial frequency, spatial orientation, and

surround contrast. This three properties allow to unify the chromatic assimilation and contrast

phenomena, as well as some other perceptual processes such as saliency perceptual processes.

The perceptual image
I
ρ
is recovered by weighting these
ω
s
,
o
wavelet coefficients using the

extended contrast sensitivity function
(e-CSF). The e-CSF is an extension of the psychophysical

CSF [
5
] considering spatial surround information (denoted by
r
), visual frequency (denoted

by
v
, which is related to spatial frequency by observation distance), and observation distance

(
d
). Perceptual image
I
ρ
can be obtained by

(1)

where
α
(
ν
,
r
) is the e-CSF weighting function that tries to reproduce some perceptual proper-

ties of the HVS. The term
α
(
ν
,
r
)
ω
s
,
o
is considered the
perceptual wavelet coefficients
of image
I

when observed at distance
d
.

3.2 Forward Inverse Quantization

Quantization is the only cause that introduces distortion into a compression process. Since

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