Image Processing Reference
In-Depth Information
Wavelet coding
This work is supported by National Polytechnic Institute of Mexico by means of Project No.
20140096, the Academic Secretary and the Commitee of Operation and Promotion of Aca-
demic Activities (COFAA), National Council of Science and Technology of Mexico by means of
Project No. 204151/2013, and LABEX Σ-LIM France, Coimbra Group Scholarship Programme
granted by University of Poitiers and Region of Poitou-Charentes, France.
1 Introduction
Region of interest (ROI) image coding is a feature that modern image coders have, which al-
lows to encode n speciic region with beter quality than the rest of the image or background
(BG). ROI coding is one of the requirements in the JPEG2000 image coding standard [ 2 , 3 ],
which defines two ROI methods [ 4 , 5 ]:
(1) Based on general scaling [ 4 ]
(2) Maximum shift (MaxShift) [ 5 ]
The general ROI scaling-based method scales coefficients in such a way that the bits associ-
ated with the ROI are shifted to higher bitplanes than the bitplanes associated with the BG, as
shown in Figure 1(b) . It implies that during an embedded coding process, any BG bitplane of
the image is located after the most significant ROI bitplanes into the bitstream. But, in some
scales depending on the scaling value, φ , some bits of ROI are simultaneously encoded with
BG. Therefore, this method allows to decode and refine the ROI before the rest of the image.
No mater φ , it is possible to reconstruct with the entire bitstream a highest fidelity version
of the whole image. Nevertheless, if the bitstream is terminated abruptly, the ROI will have a
higher fidelity than BG.
FIGURE 1 JPEG2000ROI Coding. (a) NoROI coding, (b) scaling-based ROI coding method
( φ = 3), and (c) MaxShift method, φ = 7. Background is denoted as BG, region of interest as
ROI, and bitplane mask as BPmask. MSB is the most significant bitplane and LSB is the least
significant bitplane.
The scaling-based method is implemented in five steps:
(1) A wavelet transform of the original images is performed.
(2) An ROI mask is defined, indicating the set of coefficients that are necessary for reaching a
lossless ROI reconstruction, Figure 2 .
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