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Information concealment is a technique of concealing secret utilizing excess screen informations such as images, sounds, films, paperss, etc. This technique has late become of import in a figure of application countries. For illustration, digital picture, sound, and images are progressively embedded with unperceivable Markss, which may incorporate concealed signatures or water lines that help to forestall unauthorised transcript. Recently, plentifulness of researches focus on information concealment in grayscale or colour images. Images with a low figure of colourss, such as binary images, are frequently avoided as screen media. Since the pel value in a binary image consists merely 0 and 1, it is more ambitious to conceal information than that of grayscale images. In this paper, a fresh informations concealing strategy for binary images is investigated. First, a screen image is partitioned into non-overlapping blocks, each blocks consists of pels. Then, the figure of neighbour pels with same value in each block is calculated and analyzed to happen the best of blocks for concealing information. Data spots are embedded by modifying pel values in the embeddable blocks. The concealed informations can be extracted without utilizing the original image. Compare to old work, the experimental consequences show that the concealment capacity of the proposed strategy can be doubled without giving the image quality.

Keyword: Information Hiding, Binary Image

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1. Introduction

Information concealment is a technique that inserts secret messages into a screen file, so that the being of the messages is non evident ( Lee, 2001 ) . Research in information concealment has enormous increased during the past decennary with commercial involvements driving the field. Information concealing techniques that are used today include watermarking ( Puate, 1996aˆ?Li, 2000 ) and cryptography ( Wu, 2004aˆ?Chang, 2004aˆ?Wang, 2004 ) . The major concern of watermarking is to protect the ownership of a digital content, while cryptography is to implant secret messages into digital content so that the secret messages is non noticeable.

All digital media, such as digital images, pictures and audio files, can be used to conceal secret messages ; nevertheless, digital images are frequently used for cryptography. This is because nature images normally have high grade of redundancy, which is suited to implant information without degrading the ocular quality of the image. Furthermore, images are widely used throughout the cyberspace, which normally arouses small intuition than other digital media. Plenty of researches have been focus on cryptography for grayscale or colour images. Since grayscale and colour images require 8 spots and 24 spots representation severally, this gives more room to conceal information, either in the spatial or frequence sphere. On the contrast, small research had been done for concealing informations in binary ( or two colourss ) images, which can be easy seen in scanned images, newspaper and art images. It is considered hard to conceal informations in a binary image because each pel requires merely one spots representation.

In this paper, a new informations concealment method for binary images was proposed. We will utilize the appellative conventions as followed, the image that is used to keep the secret information is named the screen image, and the image uniting the screen image and the secret information makes a stego-image. The screen image is partitioned into blocks. For each block, the characteristic value is computed, and blocks are so classified into embeddable and non-embeddable blocks. Merely embeddable blocks can be used to implant messages.

This paper is organized as follows. Section 2 is the reappraisal of related research. Section 3 describes the proposed method. Experimental consequences are given in subdivision 4 and reasoning comments are given in Section 5.

2. Literature reappraisal

Pan et Al. ( Pan, 2001 ) proposed a information concealment technique for binary images. They partition images into blocks, and each block was repartitioned into overlapping sub-blocks. Secret messages will be hidden in the halfway part of each block. Chen et Al. ( Chen, 2003 ) extended Pan ‘s work and proposed a new informations concealing method in binary image without downgrade the image quality. Following is the process of their method.

Measure 1: An image was partitioned into non-overlapping blocks of size. Each block was repartitioned into 4 overlapped sub-blocks.

Measure 2: Calculate the figure of white pels in each sub-block, the minimal figure of white pels in each sub-block is the characteristic value of the corresponding block. Messages will be embedded in a block with characteristic values from 3 to 6.

Measure 3: Blocks are sorted by leaden value, and the best block for concealment can be determined. A smaller leaden value means the distribution of pels is more unvarying, which is more suited for concealing informations.

Measure 4: The concealment location will be determined by T, the figure of sub-blocks with the same least characteristic values. If hiding spot is 1, so T must be modified to 1 or 3. If hiding spot is 0, so T must be modified to 2 or 4.

The concealed informations can be retrieved by reiterating the informations concealment procedure. After obtaining the characteristic value for each block, the figure of sub-blocks with the same least characteristic values T could be determined ; hence, the secret spots can be retrieved.

Since the block size of Chen ‘s method is restricted to, the warheads of a given image are limited. In this paper, we proposed another information concealment strategy, which can cut down the block size to to increase the warheads without downgrade the image quality.

3. The proposed method

A binary image is a digital image that has merely two possible values for each pel, that is, 0 and 1. Binary images are besides called bi-level or two-color images. Binary images are frequently used in digital image processing as a mask, or as the consequence of certain operations, such as dithering. Some printing devices, such as optical maser pressmans, fax machines can merely manage binary images.

Since a binary image is made up of pels with value 0 and 1, it is much hard to conceal secret informations either in spacial or frequence sphere. In this subdivision, we will suggest a information concealment strategy for binary image. Figure 1 depicts the procedure of informations concealing and recovering. First, a screen image is partitioned into non-overlapping blocks, and the embeddable blocks can be obtained by analyzing the construction of these blocks. If pels in a block are all black or white, so this block is considered non-embeddable, since any alterations in this block may badly degrade the image quality. After obtaining all the embeddable blocks, the characteristic value, i.e. , the maximal figure of affiliated white pels within a block, is calculated and the secret messages are so embedded harmonizing to the characteristic value. The secret message can be retrieved by the contrary mode.

Figure 1. Procedures for informations concealment and retrieving

3.1 Data concealment processs

The informations concealment procedure comprises image divider, characteristic value computation, and informations concealment. First, a cover image I is partitioned into non-overlapping blocks. Each block is composed of pels, as shown in Figure 2.

Figure 2. Image divider

For a binary screen image, each non-overlapping block is composed of several black and white sub-regions. For illustration, Figure 3 ( a ) shows a block, which is composed of 3 white sub-regions, , , and 2 black sub-regions and, whereas Figure 3 ( B ) is composed of 3 white sub-regions and 4 black sub-regions.

Figure 3. White sub-regions of a block

Suppose there are p white sub-regions, in block. Let represents the figure of white pels in white sub-region, and so the characteristic value of block is defined as

,

For illustration, in Figure 3 ( a ) , , , and ; hence, the characteristic value for block is 5.

After the characteristic value was calculated, we may implant secret informations by analyzing the characteristic value. If the spot to be embedded is 1 and is even, so we may alter a white pel in sub-region to black so that is uneven. On the other manus, if the spot to be embedded is 0 and is uneven, so a white pel in sub-region should be changed to black so that is even.

For illustration, the block shown in Figure 4 has a characteristic value 5. Suppose the secret spot we want to implant is 1. Since the characteristic value is uneven ; hence, no pel in this block has to be changed. However, if the spot we want to conceal is 0, we may alter a pel in so that is even.

Figure 4. Change one pel in a white sub-region to black to conceal 1 spot.

There are two particular instances for a block we have considered, as describe followed.

Case 1: There is merely one white pel in a block

If there is merely one white pel in a block, and the secret spot to be hidden is 0, so we have to alter one black pel adjacent to the white pel in this block to white to guarantee that is even.

Case 2: Repeated characteristic values

If there are two or more characteristic values satisfy, i.e. , there are two or more white sub-regions with the same figure of white pels, than we have to alter one pel in the boundary line of one of these sub-region to do the block become embeddable. For illustration, Figure 5 ( a ) depicts a block with 2 perennial characteristic values ( ) .

Figure 5. Change the block to go embeddable.

If this happened, so we may add one white pel to a white sub-region in order to alter the type of block to embeddable ( ) , as illustrated in Figure 5 ( B ) . After that, we may execute the secret spots implanting process, as describe in this subdivision.

Figure 6 depicts the informations concealment processs. Note that if a block has merely one white pel, or has repeated characteristic values, so the white sub-region that carries the characteristic values must be changed so that the block become embeddable.

Figure 6. Flowchart for informations concealing

3.2 informations retrieval

To recover the concealed informations, we can merely cipher the characteristic value, and so pull out the concealed spots. The process is described as followed.

Measure 1. Partition the stego-image into blocks, each block is composed of pels.

Measure 2. In each block, calculate the figure of pels in each white sub-region, so happen the characteristic value for block.

Measure 3. If the characteristic value is uneven, the concealed spot is 1 ; otherwise, the concealed spot is 0.

4. Experimental consequences.

To measure the public presentation of the proposed algorithm, four double star images ( Baboon, Boat, Lena and Pepper ) have been used as the screen image, as shown in Figure 7.

Figure 7. Original trial images

Table 1 shows the warheads of each image with different block size. In our strategy, the smallest block size is limited to, larger block size could besides be used to conceal informations. In general, the smaller the block size, the larger the warheads. If the block size is, the warheads of our strategy are at least twice than that of Chen ‘s method ( The block size of Chen ‘s method is limited to ) , as shown in Table 1.

Table 1. Hiding capacity ( spots )

Proposed

Chen

Block size

2

3

4

5

6

4

Baboon

6171

4020

2647

1831

1326

1122

Boat

3232

2328

1653

1215

911

393

Lena

2080

1480

1202

896

700

222

Pepper

1489

1182

944

750

618

320

Figure 8 shows the stego-image with a block size. Since most of the secret spots were hidden along the borders of the screen image, the stego-image and the screen image are visually identical.

Figure 8. Stego-image with block size 4-4

If a block sizewas used to conceal messages, the warhead of the screen image is larger than that of other block size. Besides, for a block size, since the altered pels will closer to the borders of images, the quality of the stego-image does non degrade due to larger warhead, as shown in Figure 9.

Figure 9. Stego-image with block size 2-2

5. Decisions

Binary images are images that have been quantized to two values, normally denoted 0 and 1. Binary images are used in many applications since they are the simplest to procedure, but concealing informations in a binary image can be a hard undertaking. Since the pel value in a binary image consists merely 0 and 1, it is more ambitious to conceal informations than that of grayscale images. In this paper, a fresh informations concealing strategy for binary images has been proposed. Secret spots are embedded harmonizing to the characteristic value of blocks. The concealed informations can be extracted without utilizing the original image. Compare with old work, the experimental consequences show that the warheads of the proposed strategy can be doubled, without giving the image quality. Future work could affect coding the secret message, or scrambling the secret message with a private key before concealment.

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