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Essay: Stow away and recover secret data in picture mosaics

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  • Stow away and recover secret data in picture mosaics
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Abstract-: In this computerized world, exchanging touchy information electronically has turned out to be inescapable. The goal of this work is to stow away and recover secret data in picture mosaics. The photograph mosaic approach has been utilized for the production of the mosaic and the minimum huge piece (LSB) system has been embraced for the installing of the shrouded data. The development of the photograph mosaic is finished by choosing a picture, part it into littler pictures (tiles) of sizes 8×8, 16×16 and 32×32. These tiles are then looked at from a lot of photographs of similar sizes. Next, the client can either conceal a mystery picture or a mystery content into them. The last mosaic picture contains mystery data that is all around disguised and is difficult to discover with the exposed eye. This strategy is more hearty contrasted with changing the bits of the first picture specifically.

Keywords— mosaic, steganography, confidentiality, secret



Today, pictures from different sources are as often as possible used and transmitted through the web for different applications, for example, online individual photo collections, secret undertaking chronicles, record stockpiling frameworks, restorative imaging frameworks, and military picture databases. These pictures normally contain private or classified data so they ought to be shielded from spillages amid transmissions. These days, numerous strategies have been proposed for securing picture transmission, for which two regular methodologies are picture encryption and information stowing away. Encryption of a picture is a methodology which utilize the common properties of pictures, for example, excess and spatial relationship, to get a picture as of now encoded which utilize the Shannon’s perplexity and dissemination properties. The picture that is scrambled turns into a picture with commotion so that nobody can acquire the transmitted mystery picture from it unless having the right key. Be that as it may, the scrambled picture still is a trivial archive, which can’t give more data before the decoding is finished. In this way, this may inspire an assailant’s consideration amid the transmission of the picture as a result of its subjective innature. Another probability to maintain a strategic distance from this issue is stowing away of information that covers a mystery message into another picture so that nobody can expect the survival of the mystery content, in which the kind of information of the mystery message that is analyzed in this paper is a picture. The strategies for information concealing definitely referred to for the most part utilize the systems, for example, LSB substitution, histogram moving, recursive histogram adjustment, discrete cosine/wavelet changes and so forth. Be that as it may, with a specific end goal to lessen the contortion of the subsequent picture, an upper headed for the twisting worth is generally determined to the payload of the cover picture. Along these lines, the fundamental restriction of the techniques for information stowing away in pictures is the trouble in inserting an immense measure of message information into one picture. In particular, in the event that one needs to conceal a mystery picture into another picture with a similar size, the mystery picture must be very compacted ahead of time. For example, for a data hiding method with an embedding rate of 0.5 bits per pixel, a secret image with 8 bits per pixel must be compressed at a rate of at least 93.75% beforehand in order to be hidden into a cover image. But, for many applications, such as keeping or transmitting medical pictures, military images, legal documents, etc., that are valuable with no allowance of serious distortions, such data compression operations are usually impractical. However, the techniques for compression of images, such as JPEG compression, are not appropriate for line drawings and graphical texts, in which sharp contrasts between neighbouring pixels are usually destroyed to become less noticeable.

In this paper, an alternate technique is proposed for the transmission of the picture safely. This technique changes the mystery picture to be transmitted into an important mosaic tile picture with a similar size which resembles another picture which was preselected as the objective picture. The procedure of change is finished with the assistance of some important data that is installed and just with the assistance of this inserted data can a man losslessly recuperate the transmitted mystery picture from the mosaic tile picture. This proposed technique is amplified by Lai and Tsai where a stylish sort of another PC picture, called mosaic tile picture, was proposed. The mosaic tile picture is the result of organizing of the tile sections of a transmitted mystery picture is disguised in another picture called the objective picture which was before chosen from the database.

This section describes the various existing schemes which are compared in this paper.

1] An Approach to Securely Transfer a Secret Image Using Reversible Color Transformations and HSV Color Model, In this paper, Ya-Lin Lee shows a technique for the transmission of the secret image securely and losslessly. This method transforms the secret image into a mosaic tile image having the same size like that of the target image which is preselcted from a database. This colour transformation is controlled and the secret image is recovered losslessly from the mosaic tile image with the help of the extracted relevant information generated for the recovery of the image.

2] Reversible Data Hiding in Encrypted Images by Reserving Room Before Encryption, In this paper, Kede Ma shows a method for data hiding into an image by reserving room before encryption of the image. This paper shows that first enough space is reserved in the image after which it is converted into encrypted form.

3] A Keyless Approach to Image Encryption, by Indian Institute of Technology Roorkee This paper shows a keyless approach to encryption methods which are used to encrypt images. We make the use of this paper to apply the keyless approach in the proposed method. This is done by generating relevant information with the help of some RMSE value which help to rotate the tile images to a certain angle.

4] JPEG: Still Image Data Compression Standard Here, W. B. Penne baker tries to explain that the main obstacle in many applications is the quantity of data required to represent a digital image. For this we would need an image compression standard to maintain the quality of the images after compression. To meet all the needs the JPEG standard for image compression includes two basic methods having different operation modes: A DCT method for “lossy” compression and a predictive method for “lossless” compression.


The embedding of text into secret image by Data Hiding, the embedding of secret image into the target image in tile form and maintaining the visibility of the original target image. The proposed method includes

1) mosaic image creation and

2) secret image recovery.

Mosaic image creation block diagram


Figure 1 : Mosaic image creation block diagram

In the primary stage, a mosaic picture is yielded, which comprises of the sections of an information mystery picture with shading amendments as indicated by a likeness measure in view of shading varieties. The stage incorporates four phases: 1)load the objective picture and that picture can be separated into equivalent squares. Fitting the tile pictures of the mystery picture into the objective pieces of a preselected target picture; 2) changing the shading normal for each tile picture in the mystery picture to wind up noticeably that of the comparing target obstruct in the objective picture; 3) turning each tile picture into a course with the base RMSE value concerning its relating target square; and 4) installing important data into the made mosaic picture for future recuperation of the mystery picture.


Figure 2: Extract secret image and target image Block diagram

In the second stage, the implanted data is extricated to recuperate about misfortune lessly the mystery picture from the produced mosaic picture. The stage incorporates two phases: 1) removing the implanted data for mystery picture recuperation from the mosaic picture, and 2) recouping the mystery picture utilizing the separated data.

A. Least Significant Bits (LSB)

The Least Significant Bit (LSB) is one of the principle procedures in spatial space picture Steganography. The LSB is the most minimal noteworthy piece in the byte estimation of the picture pixel. The LSB based picture steganography installs the mystery at all huge bits of pixel estimations of the cover picture (CVR).

The idea of LSB Embedding is straightforward. It abuses the way that the level of exactness in many picture organizations is far more noteworthy than that distinguishable by normal human vision. Along these lines, an adjusted picture with slight varieties in its hues will be unclear from the first by a person, just by taking a gander at it. In customary LSB method, which requires eight bytes of pixels to store 1byte of mystery information however in proposed LSB procedure, only four bytes of pixels are adequate to hold one message byte. Rest of the bits in the pixels continues as before.

B. Embedding Process

Initializes some parameters, which are used for subsequent data preprocessing and region selection, and then estimates the capacity of those selected regions. If the regions are large enough for hiding the given secret message, then the data hiding is performed on the selected regions. Finally, to obtain the mosaic image, it does post processing. Otherwise the scheme needs to revise the parameters, and then repeats region selection and capacity estimation until can be embedded completely. May be the parameters are different for different image content and secret message

A. Mosaic image creation algorithm

Input: a secret image S, a target image T, and a secret key K.

Output: a secret-fragment-visible mosaic image F.

Stage 1: load the target image.

Stage2:target image can be divided into blocks (8×8,16×16,32×32).

Stage 3: fitting the tile images into the target blocks.

Stage 4: performing color conversions between the tile images and the target blocks.

Stage 5: rotating the tile images.

Stage 6: embedding the secret image or text using LSB-technique.

B. Hiding the text or image algorithm:

Step1: A couple of minimum critical bits (LSB) are substituted with in information to be covered up.

Step2: The pixels are orchestrated so to speak the concealed bits before the pixel of each cover picture to limit the blunders.

Step3: Let n LSBs be substituted in every pixel.

Step4: Let d= decimal estimation of the pixel after the substitution.d1 = decimal estimation of keep going n bits of the pixel.d2 = decimal estimation of n bits covered up in that pixel.

Step5: If (d1~d2)<=(2^n)/2then no conformity is made in that pixel. Else

Step6: If(d1<d2)d = d – 2^n.If(d1>d2)d = d + 2^n.T his “d” is changed over to paired and composed back t o pixel . This strategy for substitution is straightforward and simple to recover the information and the picture quality better with the goal that it gives great security.

B. Secret image recovery algorithm

Input: a mosaic image F with n tile images {T1, T2, . . . , Tn} and the secret key K.

Output: the secret image S.

Stage 1: extracting the secret image or text recovery information.

Stage 2: recovering the secret image or text.


As show the experiments have been conducted to test the proposed method using many secret and target images with sizes 1024×768 or 768×1024. To show that the created mosaic image looks like the preselected target image, the quality metric of root mean square error (RMSE) is utilized, which is defined as the square root of the mean square difference between the pixel values of the two images.



(a) (b) (c)



(d) (e) (f)


Fig. 3. Experimental result of mosaic image creation. (a) target image. (b) secret message. (c) Mosaic image created with tile image size(d)-(f) Mosaic images created with different tile image sizes: 16×16, 24×24, 32×32, and 40×40.

Fig. 4 shows a comparison of the results yielded by the proposed method with those by Lai and Tsai, in which Fig. 4(a) is the input secret message, Fig. 4(b) is the selected target image, Fig. 4(c) is the mosaic image created by Lai and Tsai , and Fig. 4(d) is that created by the proposed method. It can be seen from these results that the mosaic image yielded by the proposed method has a smaller RMSE value with respect to the target image, implying that it is more similar to the target image in appearance. The other results of our experiments also show the same conclusion, and more importantly, the proposed method allows users to select their favorite images.



(a) (b)


(c) (d)

Fig. 4. Comparison of results of [13] and proposed method.(a) Secret message. (b) Target image. (c) Mosaic image created from (a) and (b) by [13] with RMSE= 47.651. (d) Mosaic image created from (a) and (b) by proposed method with RMSE= 33.935.


(a) (b) (c)


(d) (e) (f)

Fig. 5. Experimental result of mosaic image creation. (a) Target image. (b) Secret image. (c) Mosaic image created with tile image size(d)-(f) Mosaic images created with different tile image sizes: 8×8, 16×16, 32×32.


(a) (b)


(c) (d)

Fig. 6. Comparison of results of [13] and proposed method.(a) Secret image. (b) Target image. (c) Mosaic image created from (a) and (b) by [13] with RMSE= 37.651. (d) Mosaic image created from (a) and (b) by proposed method with RMSE= 24


A new secure image transmission method has been proposed,which not only can create meaningful mosaic images

but also can transform a secret image into a mosaic one with the same data size for use as a mask of the secret image. By the use of proper pixel color transformations as well as a skillful scheme for handling overflows and underflows in the converted values of the pixels’ colors, secret-fragment visible mosaic images with very high visual similarities to arbitrarily-selected target images can be created with no need of a target image database. Also, the original secret images can be recovered nearly losslessly from the created mosaic images. Good experimental results have shown the feasibility of the proposed method. Future studies may be directed to applying the proposed method to images of color models other than the RGB.



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