Digital image scrambling for image coding systems
US6505299B1 · kind B1 · utility
Assignee
Inventors
Key dates
| Filing date | Mar 1, 1999 |
| Grant date | Jan 7, 2003 |
| Priority date | — |
| Expiry date | Mar 1, 2019 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N21/23476
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
Methods and apparatus for encryption and decryption of digital images are disclosed. A preferred embodiment operates on an image frame after that frame has undergone a space-frequency transform operation, such as a block DCT or wavelet transform, and before the frame is passed to a bitstream coder for entropy coding. The transform coefficient map is subjected to one or more encryption operations that render a subsequently decoded (but not decrypted) image incomprehensible. These operations are designed to operate with low computational overhead and with only minor effects on compressed bit rate. They also allow secure transcoding at intermediate routers of the transmission channels without the cryptographic key.In one operation, the sign bits of transform coefficients are scrambled. In another operation, two dimensional blocks of coefficients from a common subband are shuffled and/or rotated to pseudorandom locations and orientations. In yet another operation, coefficients occupying a common “subband”, but taken from different DCT blocks, are shuffled. Still another operation shuffles motion vectors and/or scrambles sign bits for motion vector coefficients. These operat…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.