28-05-2013, 12:51 PM
New Channel Selection Rule for JPEG Steganography
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Abstract
In this paper, we present a new channel selection
rule for joint photographic experts group (JPEG) steganography,
which can be utilized to find the discrete cosine transform (DCT)
coefficients that may introduce minimal detectable distortion for
data hiding. Three factors are considered in our proposed channel
selection rule, i.e., the perturbation error (PE), the quantization
step (QS), and the magnitude of quantized DCT coefficient to be
modified (MQ). Experimental results demonstrate that higher
security performance can be obtained in JPEG steganography via
our new channel selection rule.
INTRODUCTION
STEGANOGRAPHY is a secret communication approach
that can transmit information without arousing suspicion
of the existence of the secret communication. The carrier of
steganography can be various kinds of digital media such as
image, audio, and video, etc. Due to the common use of JPEG
images, JPEG steganography has attracted much attention by
the researchers in this area.
There are two most important approaches that have been utilized
to improve the security performance of JPEG steganography.
The first one is matrix embedding [1], [2]. Through it,
less alternation needs to be made to the cover image while embedding
the same amount of information bits. The second one is
channel selection, i.e., trying to find those coefficients that may
introduce minimal detectable distortion for data hiding [3].
In [3], Fridrich et al. presented the perturbed quantization
(PQ) steganography with wet paper codes, in which the secret
message bits are embedded while the cover object is processed
with an information-reducing operation. They pointed out that
if the senders could confine the embedding changes to those
channels of the processed cover object whose values are the
most “uncertain”, higher security performance will be obtained.
Proposed Channel Selection Rule
Different from that in PQ and D-PQ, not only the PE (i.e., perturbation
error), but also the other two new factors are considered
in our channel selection rule to find the coefficients which
may introduce minimal detectable distortion for data hiding.
The first one is QS (i.e., the quantization step). As we know,
in JPEG compression, the quantization steps associated with
different frequencies are different. Fig. 2 illustrates the standard
JPEG quantization table corresponding to the quality factor
(QF) of 80. As seen, in general the quantization steps associated
with low frequencies are smaller than those with the high frequencies
according to the zig-zag order. Because the inverse discrete
cosine transform (IDCT) is a linear transformation, even if
the two unrounded DCT coefficients are with the same rounding
error, the coefficient associated with the smaller QS may result
in less information loss in the obtained JPEG image. In a similar
way, we can deduce that if the two unrounded DCT coefficients
to be modified are with the same PE, the coefficient associated
with the smaller QS may result in less distortion in the obtained
stego image.
Application of Our Channel Selection Rule
MME2 and MME3 utilize the modified binary Hamming
codes to embed secret message bits into the DCT coefficient
block with the length of . Via a new matrix embedding
methodology, MME2 and MME3 provide a simple and
practical approach to apply the D-PQ channel selection rule in
their embedding algorithm.
EXPERIMENTAL RESULTS AND ANALYSIS
In this section, experimental results and analysis are presented
to demonstrate the improvements of our new channel
selection rule on JPEG steganography. The proposed channel
selection rule is applied with the same embedding strategy as
that in MME2 and MME3 using the modified binary Hamming
codes. The algorithms utilizing our new channel selection rule
are called newMME2 (N-MME2) and new MME3 (N-MME3),
respectively. According to (3), two new factors QS and MQ are
considered in our proposed channel selection rule. If the two
control parameters corresponding to QS and MQ are selected
as , our channel selection rule will be the
same as D-PQ. Thus N-MME2 and N-MME3 will degrade into
MME2 and MME3, respectively.