Adaptive Image Self-Recovery Based on Feature Extraction in the DCT Domain

Image self-recovery aims at protecting digital images from partial damage due to accidental or malicious tampering. It is done by generating a reference code that contains the information of the image and embedding the code in the image itself. This code can later be extracted to restore the tampered regions of the image. The reference code must contain sufficient information to ensure a satisfactory reconstruction while being short enough to remain invisible when embedded in the image, which requires efficient extraction and adaptive encoding of the image information. To this end, we introduce a method for extracting local features in the DCT domain, in which the locations of the three DCT peaks, i.e., the DCT coefficients with the highest magnitudes, are examined to distinguish 13 texture profiles differing in the number of edges, edge orientations, and combinations of the two. Applying this method, we propose an adaptive image self-recovery algorithm. The DCT peaks are used to identify local texture patterns, and the bit allocation is made adaptive at hierarchical levels: 1) the texture blocks get more bit allocation than the smooth blocks; 2) the blocks having texture patterns appearing more frequently in the image are encoded with more precision; and 3) in each texture block, the highest DCT peak is assigned more bits than the remaining encoded coefficients. Hence, the encoding process is not only adaptive to the levels of variations across blocks but also to the local texture patterns. The proposed algorithm generates a reference code short enough to be embedded very comfortably in a single-least-significant-bit (LSB) plane, compared to 2 ~ 3 LSB planes often found in literature. Since the reference code contains all the critical image information in a compact form, the quality of the reconstructed images is as good as those produced by significantly longer reference codes.