General expansion-shifting model for reversible data
hiding
Xiaolong Li and Zongming Guo
Institute of Computer Science and Technology, Peking University, Beijing 100871, China
lixiaolong@pku.edu.cn, guozongming@pku.edu.cn
Abstract—Reversible data hiding (RDH) is a specific informa-
tion hiding technique in which both the embedded data and
the original cover medium can be exactly extracted from the
marked data. In this paper, we present a general expansion-
shifting model for RDH by introducing the so-called reversible
embedding function (REF) which maps each point of Z
n
to a non-
empty subset of Z
n
. Moreover, to guarantee the reversibility, the
mapped subsets of distinct points should be disjoint from each
other. With REF, RDH can be designed and the corresponding
rate-distortion formulations can be established, providing a
possibility to optimize the reversible embedding performance.
Some examples of REF are given, and a preliminary theoretical
investigation on REF is conducted as well.
I. INTRODUCTION
Reversible data hiding (RDH) is a special type of informa-
tion hiding. Being reversible, the original digital content can
be completely restored after data extraction [1]. Early RDH
methods are mainly based on lossless compression [2]–[4],
in which certain features of the cover image are losslessly
compressed to save space for embedding the payload. These
methods usually provide a low capacity and may lead to
severe degradation in image quality. Later on, more efficient
algorithms have been devised which emphasize increasing
the embedding capacity and keeping the embedding distor-
tion low. Meanwhile, several valuable reversible embedding
techniques are proposed, e.g., histogram shifting (HS) [5],
[6], difference expansion (DE) [7]–[9], prediction-error ex-
pansion (PEE) [10]–[18], and integer transform [19]–[22],
etc. Among them, the expansion-shifting based ones such as
HS and PEE have attracted considerable attention due to the
efficiency in reversible data embedding. A common feature
of expansion-shifting based RDH is that, by generating first a
histogram (e.g., the pixel-intensity histogram, the prediction-
error histogram, etc), some histogram bins are shifted to create
vacancies, while some other bins are expanded to embed data.
In this paper, we present a general expansion-shifting model
for RDH by introducing the so-called reversible embedding
function (REF) which maps each point of Z
n
to a non-empty
subset of Z
n
. In other word, REF is a function defined as
f : Z
n
7→ P(Z
n
) − {∅} where P(Z
n
) is the power set
of Z
n
. Moreover, to guarantee the reversibility, the mapped
subsets of distinct points of Z
n
should be disjoint from each
other. With the proposed REF, RDH can be designed and the
corresponding rate-distortion formulations can be established,
This work is supported by National Natural Science Foundation of China
under contract No. 61572052.
providing a possibility to optimize the reversible embedding
performance. This paper is an extension of our previous work
[23].
In the rest of this paper, the definition of REF is first
introduced in Section II. Some examples of REF are given in
this section as well. Then, some theoretical results of REF and
discussions are presented in Section III. Finally, we conclude
our work in the last section.
II. REF: DEFINITION AND EXAMPLES
REF is defined as a function
f : Z
n
7→ P(Z
n
) − {∅} (1)
where P(Z
n
) is the power set of Z
n
, i.e., P(Z
n
) is the set
consisting of all subsets of Z
n
. By this definition, for each
x ∈ Z
n
, f (x) is a non-empty subset of Z
n
. Moreover, to
guarantee the reversibility of the corresponding RDH, the REF
f should satisfy the following property
x = y =⇒ f(x) ∩ f(y) = ∅. (2)
For x ∈ Z
n
satisfying |f (x)| = 1, it will be shifted in data
embedding, where |A| means the number of elements of a
set A. On the other hand, if |f(x)| > 1, it will be expanded
to embed data. More specifically, take f(x) = {y
1
, ..., y
N
}
where N = |f(x)|, in the data embedding process,
• if N = 1, x will be directly shifted as y
1
;
• if N > 1, x will be randomly expanded as one of y
i
.
Notice that, with the condition (2), the original cover recovery
is obvious: for a given marked data y, it can be recovered as
f
−1
(y). Then, we see that a RDH scheme can be derived
based on a given REF.
With REF, the rate-distortion formulations can be estab-
lished for the corresponding RDH scheme. Consider here the
n-dimensional histogram of the cover data which is a function
h : Z
n
7→ Z
+
(3)
Notice that, the histogram maybe the pixel-intensity histogram,
the prediction-error histogram, etc. Then, based on the afore-
mentioned data embedding process, we see that the embedding
capacity and the embedding distortion denoted respectively as
EC(f) and ED(f) can be formulated as
EC(f) =
x∈Z
n
h(x) log
2
|f(x)| (4)