Adaptive LSB Substitution and Combination of LSB Substitution, PVD, and EMD

Adaptive LSB Substitution and Combination of LSB Substitution, PVD, and EMD

DOI: 10.4018/978-1-5225-7516-0.ch006

Abstract

This chapter describes two types of steganography techniques: (1) adaptive LSB substitution and (2) combination of LSB substitution, PVD, and exploiting modification directions (EMD). The adaptive LSB substitution technique embeds a variable number of bits in different pixel blocks depending on the smoothness of the block. This improves the security and reduces the distortion. In the second technique, the LSB substitution, PVD, and exploiting modification directions (EMD) principles are judiciously combined in pixel blocks to get higher embedding capacity, lesser distortion, and improved security. These hybrid techniques survive from both RS analysis and pixel difference histogram (PDH) analysis.
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Introduction

There are two categories of steganography techniques discussed in this chapter. The first category is called adaptive LSB substitution. The adaptive LSB substitution techniques calculates the average pixel value difference in a block. based on this difference the number of LSBs to be embedded is decided. There are two techniques of this category described in this chapter. The first technique uses 2×2 pixel blocks and divides the blocks into two types such as lower and higher, based on the average pixel value difference (Liao, Wen, & Zhang, 2011). In lower block, a smaller number of bits can be hidden and in higher block, a greater number of bits can be hidden. Similarly, the second technique uses 3×3 pixel blocks and divides the blocks into four categories based on average pixel value difference (Swain, 2014).

The second category of techniques is a combination of LSB substitution, PVD and EMD (Pradhan, Sekhar & Swain, 2018). There are two techniques in this category. The first one uses 2×2 pixel blocks and the second one uses 3×3 pixel blocks.

Zhang and Wang (2006) proposed exploiting modification direction (EMD) steganography. The principal goal in it is that a group of secret bits be converted to a digit in (2n+1)-ary notational system, where n is the size of pixel block. This secret digit could be hidden in the pixel block by adding ±1 to only one pixel. In this technique the hiding capacity is not good. Shen and Huang (2015) made the hiding capacity of a block adaptive by using PVD with EMD. This PVD with EMD technique provides higher hiding capacity and better PSNR. To protect from pixel difference histogram (PDH) analysis and RS analysis, two hybrid image steganography techniques by appropriate combination of LSB substitution, pixel value differencing (PVD) and exploiting modification directions (EMD) has been proposed in (Pradhan, Sekhar & Swain, 2018).

As all the above techniques use both the LSB substitution and PVD principle, so both RS analysis (Fridrich, Goljian & Du, 2001; Swain & Lenka, 2015) and pixel difference histogram (PDH) analysis (Zhang & Wang, 2004; Pradhan, Sahu, Swain & Sekhar, 2016) could be used to check the security strength in them.

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