ENCRYPTION AND DECRYPTION OF DIGITAL COLOR IMAGE SIGNALS

摘要

A colour image signal is partially encrypted and decrypted. At least part of the data that represents a luminance component of the source colour image signal is encrypted and inserting in the partially encrypted digital image signal. All colour properties of pixel values from the source colour image that have luminance according to the luminance component are inserted without encryption. Preferably, the source colour image signal is copied into the partially encrypted digital image signal, except for a replacement of the luminance component by the encrypted data. Also preferably encryption is applied only a zero frequency coefficient of a Discrete Cosine transform of luminance components for the pixel locations in the block and non-zero frequency coefficients of the Discrete Cosine Transform. In a further embodiment a subset of the blocks is selected for the encryption of data derived from the zero frequency coefficients, and luminance information of the blocks outside the subset is inserted into the partially encrypted digital image signal without encryption.