Information Technology Reference
In-Depth Information
low-pass and high-pass filtering (filters
h
and
g
in Figure 5 respectively) suc-
ceeded by dyadic downsampling on the rows of the original image. The resulting
image is thereafter vertically decomposed by applying similar operations on its
columns. The entire operation yields a set of four subbands, each having half of
the resolution of the original image. The subband resulting from low-pass filtering
on both rows and columns is called the LL-subband and represents a lower resolu-
tion approximation of the original image. The remaining subbands are referred to
as the LH, HL and HH subbands (see Figure 5) and respectively contain the high-
frequency horizontal, vertical and diagonal details representing the information
difference between the original image and the LL-subband. Additional decomposi-
tion levels are computed by performing the aforementioned operations on the
LL-subband of the previous decomposition level.
Fig. 4
Overview of a JPEG 2000 Part 1 encoder
Fig. 5
Two-dimensional wavelet-transform with 2 decomposition levels
