A new lossy compression scheme for encrypted gray-scale images

Compression of encrypted data has attracted considerable research interests nowadays due to distributed processing and cloud computing. In this work, we propose a novel lossy compression scheme for encrypted gray-scale images. The original image is first divided into non-overlapping blocks. Then, it is encrypted by a modulo-256 addition and block permutation. In compression phase, the spatial correlation and quantization are exploited to reduce the compression ratio. At the decoder side, context-adaptive interpolation with an image-dependent threshold is used to make image reconstruction precise. Experimental results show that the proposed scheme achieves better performance compared to the previous work.