Image Processing Reference
Algorithm 2 shows how a given subset S 0 is divided into four equal parts (line 6) and how
the significance test (lines 7-12) is performed, resulting in four subsets ( S 1 , S 2 , S 3 , and S 4 ) with
their respective significance stored at the end of . Subsets S 1 , S 2 , S 3 , and S 4 are four 2 × 1
cell arrays. The fist cell of each array contains one of the four subsets extracted from S 0 ( S i (1))
and the second one stores its respective significance test result ( S i (2)).
ALGORITHM 2 Subset significance test.
3.3 Coding Algorithm
ing, and refinement, which are described in the following subsections. SPIHT uses three
ordered lists, namely, the list of insignificant pixels (LIP), the list of significant sets (LIS), and the
list of significant pixels (LSP). The later list represents just the individual coeicients, which are
considered the most important ones. SPECK employs two of these lists, the LIS and the LSP.
Whereas H i -SET makes use of only one ordered list, the LSP.
Using a single LSP place extra load on the memory requirements for the coder, since the
total number of significant pixels remains the same even if the coding process is working in
insignificant branches. That is why H i -SET employs spare lists, storing significant pixels in
several sub-lists. These smaller lists have the same length than significant coefficients founded
in the processed branch. With the purpose of expediting the coding process it is used not only
spare lists, but also spare cell arrays, both are denoted by an prime, LSP′, H′, or , for instance.
(1) Initialization Pass : The first step is to define threshold thr as
that is, thr is the maximum integer power of two not exceeding the maximum value found at