qGBbBShift - Emerging Trends in Image Processing, Computer Vision, and Pattern Recognition - page 137

The perceptual inverse quantizer (I-ρSQ) or the recovered introduces perceptual cri-

teria to the classical Inverse Scalar Quantizer and is given by

(5)

3.2 ρGBbBShift Algorithm
In order to have several kinds of options for bitplane scaling techniques, a perceptual gener-
alized bitplane-by-bitplane shift (ρGBbBShift) method is proposed. The ρGBbBShift method
introduces to the GBbBShift method perceptual criteria when bitplanes of ROI and BG areas
are shifted. This additional feature is intended for balancing perceptual importance of some
coefficients, regardless of their numerical importance and for not observing visual diference
at ROI regarding MaxShift method, improving perceptual quality of the entire image.
Thus, ρGBbBShift uses a binary bitplane mask or BPmask in the same way that GBbBShift
( Figure 3(c) ) . At the encoder, shifting scheme is as follows:
(1) Calculate φ using Equation (1) .
(2) Verify that the length of BPmask is equal to 2 φ .
(3)

• For all ROI Coefficients, forward perceptual quantize them using Equation (4) (F-ρSQ)
with viewing distance d 1 .
• For all BG coefficients, forward perceptual quantize them using Equation (4) (F-ρSQ)

with viewing distance d 2 , being d 2 d 1 .

(4) Let τ and η be equal to 0.
(5) For every element i of BPmask, starting with the least significant bit:
• If BPmask( i ) = 1, Shift up all ROI perceptual quantized coefficients of the ( φ − η )th bit-
plane by τ bitplanes and increment η .
• Else: Shift up all BG perceptual quantized coefficients of the ( φ − τ )th bitplane-by- η- bit-
planes and increment τ .
At the decoder, shifting scheme is as follows:
(1) Let φ = length of BP mask /2 be calculated.
(2) Let τ and η be equal to 0.
(3) For every element i of BPmask, starting with the least significant bit:
• If BPmask( i ) = 1, Shift down all perceptual quantized coefficients by τ bitplanes, which
pertain to the (2 φ − ( τ + η ))th bitplane of the recovered image and increment η .
• Else: Shift down all perceptual quantized coefficients by η bitplanes, which pertain to the
(2 φ − ( τ + η ))th bitplane of the recovered image and increment τ .
(4) Let us denote as c i , j a given non-zero wavelet coefficient of the recovered image with 2 φ bit-
planes and c i , j as a shifted down c obtained in the previous step, with φ bitplanes: