结合块旋转和马赛克拼图的生成式伪装方法通过在嵌密位置放置与待隐藏秘密信息相关的圆形图像对秘密信息进行表达，会导致生成的马赛克图像的视觉质量较差，而较差的视觉质量也容易导致隐藏的秘密信息发生泄漏.为避免该问题，提出一种改进块旋转和马赛克拼图的生成式伪装方法.在该方法中，首先将多个灰度图像转换为圆形图像并按像素均值增序排列作为编码图像，将掩体图像直接通过误差扩散预处理转化为多级半色调图像；其次，通过随机坐标序列来决定秘密信息的隐藏位置，通过生成随机加密映射矩阵对秘密信息进行加密映射处理；最后，遍历掩体图像选取像素值对应的编码图像，对于隐藏和非隐藏位置，分别将编码图像旋转与秘密信息相关角度和随机角度，进而生成马赛克图像.在提取时，根据密钥结合质心旋转匹配策略以及区间认证策略对秘密信息进行认证以提高秘密信息认证的精度.实验表明，所提方法直接用编码圆形图像的旋转角度来表达秘密信息，在放置过程中始终选取以掩体像素值相对应的编码圆形图像来表达秘密信息，因而不会产生任何偏差，也不会导致任何视觉质量下降，具有良好的视觉质量.该方法引入了区间认证策略，具有较高的认证精度，所提方法具有较强的抗攻击鲁棒性且提取过程完全依赖于密钥，具有较高的安全性.
The conventional generation camouflage method combined with block rotation and photo mosaic expresses secret information by placing the circular images related to secret information in the embedding position, thus leading to a poor visual quality of resulted mosaic image and the leakage of hidden secret information. To address this, an improved generation camouflage method combined with block rotation and photo mosaic is proposed in this paper. In the method, firstly several grayscale images are converted into circular images and arranged as encoded images according to the ascending order of pixel mean value, and the cover image is directly transformed into the multiple halftone image by error diffusion. Secondly, the hidden positions of secret information are determined by random coordinate sequences, and the secret information was encrypted and mapped by generating random encryption mapping matrix. Finally, the coded images with the corresponding pixel values are selected by traversing the cover image. For the hidden and unhidden positions, the encoded images are rotated by a determined angle relative to secret information and a random angle respectively to generate a photo mosaic image. In order to improve the accuracy of secret information authentication, secret information is authenticated by the user key combined with centroid rotation matching strategy and interval authentication strategy. Experiments show that the proposed method directly uses the rotation angle of the encoded circular image to express secret information and it always selects the encoded circular image corresponding to the pixel value in the cover image to express secret information, so it neither brings any deviation nor causes any visual quality degradation. The proposed method performs strong anti-attack robustness and high security due to the entire key-dependency in extraction process.
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