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
0.564344 0.285968
0.179609 0.043903
0.014774 0.000573
3 Perceptual quantization
3.1 Contrast Band-Pass Filtering
The CBPF [ 4 ] is a low-level perceptual model of the HVS. It estimates the image perceived by
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
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
each transform sample at the perceptual image I ρ (1) is mapped independently to a corres-
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