Secure Image Coding

Input image

Encryption schemes based on visual cryptography principles are designed to ensure the confidentiality of binary or binarized images. To take into account the special properties of gray-scale and color images, an image secret sharing framework with perfect reconstruction of the secret image has been introduced. However, such solutions may not be suitable when transmitting large still images and video via public wireless and mobile networks, as the visual material can be overwhelming to transmit due to its large size necessitating the use of complex compression algorithms.

Image decoded without key

Efficiently encrypting still color images is usually based on the principle of partial or selective encryption and relies on the compression algorithm, for example color set partitioning in hierarchical trees compression, in order to produce a secure coded image. It directs a stream cipher to encrypt only certain significance bits, resulting thus in minimal computational overhead. To unaffect the rate-distortion performance of the compression algorithm, specific bits of the image should be encrypted after encoding. Both efficiency and confidentiality of the approach is ensured by encrypting only the significance bits of individual coefficients and determining how many coding iterations for which the encryption should be performed. The confidentiality of the image also results from the unknown arrangement of encrypted and unencrypted bits. The principles behind the presented solution may be applied to various embedded image and video coders.

References:   R. Lukac and K.N. Plataniotis, Secure Color Imaging. In Color Image Processing: Methods and Applications, (eds.) R. Lukac and K.N. Plataniotis, CRC Press / Taylor & Francis, pp. 185-202, October 2006. ISBN 0-8493-9774-X K. Martin, R. Lukac and K.N. Plataniotis, "Efficient Encryption of Wavelet-Based Coded Color Images," Pattern Recognition, vol. 38, no. 7, pp. 1111-1115, July 2005.