Perceptual cryptography on SPIHT compressed images or videos

Perceptual cryptography encrypts multimedia data in the compression domain and causes some degradation to the decoded data. If customers are interested in the multimedia data, they can pay for one of higher quality. A perceptual cryptography on SPIHT encoded images or videos is presented. By confusing different numbers of wavelet coefficients and encrypting different numbers of coefficients´ signs, the images or videos can be degraded to different degrees. The encryption strength can be adjusted according to a certain quality factor, the technique supports direct bit-rate control, and is of low cost, which makes it suitable for multimedia applications with a real-time operating requirement, such as video conferencing, multimedia networks, mobile multimedia, and so on.