Image Processing Reference

In-Depth Information

FIGURE 2
ROI mask generation, wavelet domain.

(3) Wavelet coefficients are quantized and stored in a sign magnitude representation, using the

most significant part of the precision. It will allow to downscale BG coefficients.

(4) A specified scaling value, , downscales the coefficients inside the BG.

(5) The most significant bitplanes are progressively entropy encoded.

The input of ROI scaling-based method is the scaling value
φ
, while MaxShift method cal-

culates it. Hence, the encoder defines from quantized coefficients this scaling value such that,

(1)

where max{MBG} is the maximum coefficient in the BG. Thus, when ROI is scaled up
φ
bit-

planes, the minimum coefficient belonging to ROI will be place one bitplane up of BG (
Figure

1(c)
). Namely, 2
φ
is the smallest integer that is greater than any coefficient in the BG. MaxShift

method is shown in
Figure 1(c)
.
Bitplane mask (BPmask) will be explained in
Section 2.1
.

At the decoder side, the ROI and BG coefficients are simply identified by checking the coef-

icient magnitudes. All coefficients that are higher or equal than the
φ
th bitplane belong to the

ROI, otherwise, they are a part of BG. Hence, it is not important to transmit the shape informa-

tion of the ROI or ROIs to the decoder. The ROI coefficients are scaled down
φ
bitplanes before

inverse wavelet transformation is applied.

2 Related work

2.1 BbB Shift

Wang and Bovik proposed the bitplane-by-bitplane shift (BbBShift) method in Ref. [
6
].

BbBShift shifts bitplanes on a bitplane-by-bitplane strategy.
Figure 3(a)
shows an illustration

of the BbBShift method. BbBShift uses two parameters,
φ
1 and
φ
2, whose sum is equal to the

number of bitplanes for representing any coefficient inside the image, indexing the top bit-

plane as bitplane 1. Summarizing, the BbBShift method encodes the first
φ
1 bitplanes with ROI

coeicients, then, BG and ROI bitplanes are alternately shifted, refining gradually both ROI

and BG of the image (
Figure 3(a)
). The encoding process of the BbBShift method is defined as

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