Parameter analysis of fractal image compression and its
applications in image sharpening and smoothing
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Jianji Wang
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, Nanning Zheng, Yuehu Liu, Gang Zhou
Institute of Artificial Intelligence and Robotics, Xi’an Jiaotong University, Xi’an 710049, China
article info
Article history:
Received 16 July 2012
Accepted 19 December 2012
Available online 5 January 2013
Keywords:
Fractal image compression
Image contrast
Affine parameter
Image sharpening and smoothing
abstract
In recent years, numerous fractal image compression (FIC) schemes and their applications
in image processing have been proposed. However, traditional FIC ignores the importance
of affine parameters in the iterated function system (IFS) and affine parameters are kept
invariant for a certain image in almost all of these schemes. By analyzing fractal
compression technology in this paper, we show that the affine parameters in IFS can vary
with different image quality measurements. A positive correlation exists between the
image contrast of fractal decoded image and affine scalar multiplier. This strong correla-
tion demonstrates that an image can be sharpened or smoothed using fractal compression
technology.
& 2012 Elsevier B.V. All rights reserved.
1. Introduction
Fractal image compression (FIC) is an image coding
technology based on fractal geometry. The first FIC scheme
which applied the iterated function system (IFS) to image
compression was proposed by Barnsley in 1988 [1].How-
ever, FIC was widely applied after Barnsley’s graduate
student Jacquin implemented the algorithm automatically
using the partitioned iterated function system (PIFS) in
1992 [2]. Since then, the FIC technology has demonstrated
rapid development.
In fractal compression, an image is encoded by a PIFS
whose attractor is close to the original image. These
parameters and corresponding position information of
block pairs are stored instead of the original image to
decrease the storage space occupied by the image. Aside
from its application as an image coding method, FIC has
been widely applied in other image processing fields,
including image indexing and retrieval [3], image encryp-
tion [4], image denoising [5–8], image authentication
[9,10], and some pattern recognition problems such as
facial image recognition [11].
Numerous FIC schemes have been published, which
cover almost all parts involved in fractal compression
[12–14]. Most published studies have focused on accel-
erating encoding [15–22] and decoding [23,24], and
improving the visual quality of a decoded image
[5,25–27]. The research on affine parameters is only
limited to their effect on the convergence of IFS.
The contractility of IFS can be guaranteed by setting the
affine multiplier s o 1 [28]. However, empirical evidence
indicates that contractility is often achieved for larger
values of the affine multiplier s [12,29]. The traditional FIC
scheme uses mean squared error (MSE) to evaluate the
self-similarity between blocks in which affine parameters
are invariant for a certain image, and a new scheme with
a new image measurement has also been proposed [25].
The effect of gradually changing affine multiplier on
the fractal decoded image is discussed in this paper. First,
we show that the affine parameters of IFS can vary with
Contents lists available at SciVerse ScienceDirect
journal homepage: www.elsevier.com/locate/image
Signal Processing: Image Communication
0923-5965/$ - see front matter & 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.image.2012.12.006
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This work was supported in part by the Program 973 No.
2012CB316400, and the National Natural Science Foundation of China
(NSFC) Nos. 91120009, 61175010, and 60903122, and the Specialized
Research Fund for the Doctoral Program of Higher Education (SRFDP) No.
20090201110029.
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Corresponding author. Tel.: þ86 29 82668672.
E-mail addresses: jianjiwang@foxmail.com (J. Wang),
nnzheng@mail.xjtu.edu.cn (N. Zheng), liuyh@mail.xjtu.edu.cn (Y. Liu),
Gang.Zhou@stu.xjtu.edu.cn (G. Zhou).
Signal Processing: Image Communication 28 (2013) 681–687