Cryptography Reference
In-Depth Information
8.5.2 JPEG2000-BPCS Steganography
Basically, secret data can be embedded in the bit-plane representation of the
quantized wavelet coe
cients after quantization step, provided that the rate-
distortion optimization of JPEG2000 is bypassed. However, this procedure,
which determines the optimal number of bit-planes for a given bit rate, is an
essential part of the codec which contributes to its high compression e
ciency.
Thus, to avoid compromising the compression e
ciency of JPEG2000, data
embedding by BPCS is decided to be performed right after ROI descaling in
decoding process where the optimal bit-plane structure for a given bit rate
is available. The procedure for data embedding and extraction in JPEG2000-
BPCS steganography is shown in Fig. 8.12.
Image Data
Pre-Processing
DWT
Secret Data
Secret Data
BPCS
(Extraction)
BPCS
(Embedding)
Quantization
ROI
Scaling
ROI
Descaling
ROI
Scaling
Arithmetic
Encoder
(Tier-1 Coding)
Arithmetic
Decoder
(Tier-1 Decoding)
Arithmetic
Encoder
(Tier-1 Coding)
Bit-Stream
Organization
(Tier-2 Coding)
Bit-Stream
Unorganization
(Tier-2 Decoding)
Bit-Stream
Organization
(Tier-2 Coding)
Bit-Stream
Bit-Stream
(Embedded)
Fig. 8.12.
A flowchart of data embedding and extraction in JPEG2000-BPCS
steganography.
The entire process to embed data in JPEG2000-BPCS steganography
follows the solid line arrows shown in Fig. 8.12. An image is encoded into
JPEG2000 bit-stream, whose size can be met almost exactly to a target bit
rate (bit per pixel; bpp). The encoding process is shown in the left part of
Fig. 8.12; from pre-processing to bit-stream organization. The JPEG2000 bit-
stream (compressed image file) is then decoded, but decoding is halted right
after ROI descaling. The information at this point is used to construct the bit-
planes of quantized wavelet coe
cients and then used to embed secret data
