An oblivious fragile watermarking scheme for images utilizing edge transitions in BTC bitmaps
As one of the famous block-based image coding schemes, block truncation coding (BTC) has been also applied in digital watermarking. Previous BTC-based watermarking or hiding schemes usually embed secret data by modifying the BTC encoding stage or BTC-compressed data, obtaining the watermarked image with poorer quality than the BTC-compressed version. This paper presents a new oblivious image watermarking scheme by exploiting BTC bitmaps. Unlike the traditional schemes, our approach does not really perform the BTC compression on images during the embedding process but utilizes the parity of the number of horizontal edge transitions in each BTC bitmap to guide the watermark embedding and extraction processes. The embedding process starts by partitioning the original cover image into non-overlapping 4x4 blocks and performing BTC on each block to obtain its BTC bitmap. One watermark bit is embedded in each block by modifying at most three pixel values in the block to make sure that the parity of the number of horizontal edge transitions in the bitmap of the modified block is equal to the embedded watermark bit. In the extraction stage, the suspicious image is first partitioned into non-overlapping 4x4 blocks and BTC is performed on each block to obtain its bitmap. Then, by checking the parity of the number of horizontal edge transitions in the bitmap, we can extract one watermark bit in each block. Experimental results demonstrate that the proposed watermarking scheme is fragile to various image processing operations while keeping the transparency very well.
block truncation coding fragile image watermarking oblivious watermarking data hiding image authentication