# Reversible Data Hiding for DICOM Image Using Lifting and Companding
## 1 Introduction  
Rapid advancement in digital techniques had transformed the style of storage and transmission of multimedia data. With the availability of the communication network and the World Wide Web (WWW), digital data can travel from one source to an endless range of destination in any part of the globe. Notwithstanding these advantages, the digital domain representation of data also has a downside. The artworks in the form of a digital image can be used illegally, tampered with, and copied with an eye to copyright violation. This property of digital technology has encouraged thieves and discouraged the creator and the owner of digital artworks. Digital data hiding (watermarking) becomes a potential solution to address the above problems. Data hiding is a method of inserting an auxiliary message within the original data satisfying a few essential requirements [1; 2]. However, it is very difficult to meet all these requirements simultaneously with the highest degree of accuracy. The design of data hiding techniques governed by widely diverse factors such as character and availability of the cover data, visibility/non-visibility of metadata, choice of embedding space and location, degree of resiliency against unintentional or intentional attacks on the data, etc. The watermark can be embedded in the spatial domain or frequency domain depending on the desired application. It is seen that the frequency domain methods are more robust than the spatial domain techniques [3]. The large numbers of data hiding techniques modify the cover media in order to embed the watermark information. The modification is very small and imperceptible to human visual systems (HVS). However, the original cover media cannot be restored entirely. In other words, those schemesare irreversible data hiding techniques. But the irreversibility is not permissible to some applications, such as legal, forensic image archiving, and medical imaging [4]. Medical images are normally collected in hospitals or research centers due to the nature of the specialized equipment [5]. There are standard means like DICOM (Digital Imaging and Communications in Medicine) that enable the management, storage, and impression of medical images in standard formats [6]. For medical imaging applications, reversible data hiding is used to extract the embedded information as well as to restore the original host signal. In other words, reversible watermarking schemes are also often known to as lossless, invertible, or distortion-free, data hiding technique, and it is a very prominent research area in the last few years [4]. The idea of a reversible watermarking technique initially proposed and patented by Eastman Kodak [7]. [PERSON] et al. [4] embed watermark information into the high-frequency wavelet coefficients by companding technique. The Laplacian-like distribution of integer wavelet coefficients helps to select the compression and expansion functions. [PERSON] et al. [8] develop a novel encryption scheme to serve the purpose of data hiding in the reversible domain. Their scheme improves the embedding capacity with a minimum computational burden. [PERSON] [9] described a reversible watermarking scheme based on difference expansion (DE). This scheme uses location map to embed watermark. The term 'location map' is the selected positions of the pixels or the coefficients. The method selects the pixels or the coefficients from the location map to modulate during the process of watermark embedding. The major drawback of this scheme is the lack of capacity control due to insertion of the compressed location map in conjunction with the true payload. Hence the system will suffer from low embedding rate and also the lack of visual quality of the watermarked image. [PERSON] and [PERSON] [10] proposed a reversible data hiding scheme using bit-plane coding and wavelet transform based on lifting. The performance of the scheme for several types of noise and attacks is tested.