In lossless watermarking, it is possible to completely remove the embedding distortion from the watermarked image
and recover an exact copy of the original unwatermarked image. Lossless watermarks found applications in fragile
authentication, integrity protection, and metadata embedding. It is especially important for medical and military
images. Frequently, lossless embedding disproportionably increases the file size for image formats that contain lossless
compression (RLE BMP, GIF, JPEG, PNG, etc...). This partially negates the advantage of embedding information as
opposed to appending it. In this paper, we introduce lossless watermarking techniques that preserve the file size. The
formats addressed are RLE encoded bitmaps and sequentially encoded JPEG images. The lossless embedding for the
RLE BMP format is designed in such a manner to guarantee that the message extraction and original image
reconstruction is insensitive to different RLE encoders, image palette reshuffling, as well as to removing or adding
duplicate palette colors. The performance of both methods is demonstrated on test images by showing the capacity,
distortion, and embedding rate. The proposed methods are the first examples of lossless embedding methods that
preserve the file size for image formats that use lossless compression.
For most data hiding applications, the main source of concern is the effect of lossy compression on hidden information. The objective of watermarking is fundamentally in conflict with lossy compression. The latter attempts to remove all irrelevant and redundant information from a signal, while the former uses the irrelevant information to mask the presence of hidden data. Compression on a watermarked image can significantly affect the retrieval of the watermark. Past investigations of this problem have heavily relied on simulation. It is desirable not only to measure the effect of compression on embedded watermark, but also to control the embedding process to survive lossy compression. In this paper, we focus on oblivious watermarking by assuming that the watermarked image inevitably undergoes JPEG compression prior to watermark extraction. We propose an image-adaptive watermarking scheme where the watermarking algorithm and the JPEG compression standard are jointly considered. Watermark embedding takes into consideration the JPEG compression quality factor and exploits an HVS model to adaptively attain a proper trade-off among transparency, hiding data rate, and robustness to JPEG compression. The scheme estimates the image-dependent payload under JPEG compression to achieve the watermarking bit allocation in a determinate way, while maintaining consistent watermark retrieval performance.