A novel image transmission method based on mosaic image creation and secret image recovery for electric power security

Image transmission is very important for various applications. In order to ensure the security of image transmission, a novel image transmission method based on mosaic image creation and secret image recovery is proposed. The proposed method has two phases: 1) Mosaic image creation. A mosaic image is generated, which includes the fragments of an input secret image with color corrections according to a similarity criterion based on color variations. 2) Secret image recovery. Based on the received signal, the secret image is recovered losslessly from the generated mosaic image. Experimental results show that the proposed method has better feasibility.


Introduction
Electric power security is very important for social development. Therefore, real-time monitoring of electric power security is very important. As an important way of information transmission, image is applied to electric power security. These images usually contain private information so that they should be protected during transmissions. Hence, many scholars have proposed some methods for securing image transmission, and the commonly methods are image encryption and data hiding.
Image encryption is a technique that utilizes the natural properties of images, to get an encrypted image based on Shannon's confusion and diffusion properties [1][2][3][4][5]. Some researchers have proposed many schemes to improve the image transmission problem. In [1], a block scrambling-based encryption method is proposed to enhance the security of Encryption-then-Compression systems with JPEG compression, which allow us to securely transmit the images through an untrusted channel provider, such as social network service providers. A digital image encryption algorithm based on bit-planes is proposed in [2], and experimental results show that the proposed algorithm offers good encryption. In [3], a new framework for the chaos-based quantum encryption of healthcare images is proposed. According to the DNA encryption algorithm and the double-chaotic system which contains the optical chaos and the coupled map lattice chaotic system, the authors of [4] proposes a novel image encryption-then-transmission system. In [5], in order to improve encryption power, on the premise of maintaining the JPEG's compression efficiency, a new joint image compression and encryption scheme based on a lossy JPEG standard is proposed.
As another important means, data hiding has been studied by many scholars [6][7][8][9][10]. In order to achieve high perceptual quality of images and video at the end-user despite channel losses, a robust error concealment scheme based on data hiding is proposed in [6]. The scheme involves embedding a low-resolution version of each image or video frame into itself using spread-spectrum watermarking, extracting the embedded watermark from the received video frame, and using it as a reference for reconstruction of the parent image or frame, thus detecting and concealing the transmission errors. In [7] propose a new reversible method based on MSB (most significant bit) prediction with a very high capacity. In order to improve the error resilience of object-based video by adaptively embedding the shape and motion information into the texture data, a new data hiding scheme is proposed in [8].
The above analysis mainly discusses image encryption and data hiding. In order to ensure image transmission for electric power security, we propose a novel image transmission method based on mosaic image creation and secret image recovery. The proposed method is inspired by the method in [10].
The rest of this paper is organised as follows. The proposed method is proposed in Section 2. In Section 3, the performance is discussed. Finally, conclusion is given in Sections 4.

Proposed method
In order to secure the image transmission, a novel image transmission method is proposed, which includes two phases: mosaic image creation and secret image recovery.
(1) Mosaic image creation. According to a similarity criterion of color variations, a mosaic image is generated, which contains the fragments of an input secret image with color corrections. The phase includes four stages: a) fit the tile images of the secret image into the target blocks of a preselected target image; b) transform the color characteristic of each tile image in the secret image to become that of the corresponding target block in the target image; c) rotate each tile image into a direction with the minimum root mean square error (RMSE) value with respect to its corresponding target block; and d) embed relevant information into the created mosaic image for future recovery of the secret image. (2) Secret image recovery. Based on the received signal, the secret image is recovered losslessly from the generated mosaic image. The phase includes two stages: a) Extract the received signal for secret image recovery from the mosaic image; b) Recover the secret image based on the extracted information. Suppose where ' c c c q/   , and c r,g, b  . The detailed algorithms for Algorithm 1 is mosaic image creation, Algorithm 2 is secret image recovery.

Algorithm 1
Input: secret image T , a target image Q , secret key K . Output: a secret-fragment-visible mosaic image D . Stage 1: fit the tile images into the target blocks.
1. If the size of the target image Q is different from that of the secret image T , change the size of Q to be identical to that of T ; and divide the secret image T into n tile images  

Algorithm 2
Input: a mosaic image D with n tile images   4. Decompose t N into n bit streams 1 N through n N for the n to-be-constructed tile images 1 Q through n Q in T , respectively. 5. Decode i M for each tile image i Q to obtain the following data items: 1) the index i j of the block ji A in D corresponding to i Q ; 2) the optimal rotation angle of i Q ; 3) the means of i Q and ji A and the related standard deviation quotients of all color channels; and 4) the overflow/underflow residual values in i Q decoded by the Huffman table HT. Stage 2: recovering the secret image. 6. Recover one by one in a raster-scan order the tile images i Q , i1  through n , of the desired secret image T by the following steps: 1) rotate in the reverse direction the block indexed by i j , namely ji A , in D through the optimal angle and fit the resulting block content into i Q to form an initial tile image i Q ; 2) use the extracted means and related standard deviation quotients to recover the original pixel values in i Q according to (4); 3) use the extracted means, standard deviation quotients, and (5) to compute the two parameters S c and L c ; 4) scan i Q to find out pixels with values 255 or 0 which indicate that overflows or underflows, respectively, have occurred there; 5) add respectively the values L c or S c to the corresponding residual values of the found pixels; 6) take the results as the final pixel values, resulting in a final tile image i Q . 7. Compose all the final tile images to form the required secret image T as output.

Performance evaluation
In this section, we numerically examine the performance of our proposed method. In our experiments, an electric environment is provided for our experiments, and the sizes of target images is 1024×768. To show that the created mosaic image looks like the preselected target image, the quality metric of root mean square error (RMSE) is adopted, which is considered as the square root of the mean square difference between the pixel values of the two images.    Figure 1 (d) is the mosaic image according to the proposed method with RMSE=40. It can be obtained from these results that the mosaic image generated by the proposed method has a smaller RMSE value with respect to the target image, and it is more similar to the target image. According to the experimental results, the proposed method is better than the method in [10]. For privacy, users can select specific images as target images.

Conclusion
In this paper, a novel image transmission method based on mosaic image creation and secret image recovery is proposed for the security of image transmission. According to the proposed method, images can be transmitted safely, and the original secret images can be recovered nearly losslessly from the created mosaic images. Experimental results show that the proposed method has better feasibility. Therefore, the proposed method will be further improved for image transmission of electric power security.