Other Free Encyclopedias » Online Encyclopedia » Encyclopedia - Featured Articles » Contributed Topics from A-E

Embedding Multiple Watermarks in a Transform Domain

image embedded band low

Definition: Multiple watermarks can be embedded in an image by using different subbands.

In a recent non-blind watermarking paper, two visual watermarks are embedded in the DWT domain through modification of both low and high values of DWT coefficients. Since the advantages and disadvantages of lower and higher subband watermarks are complementary, embedding multiple watermarks in an image would result in a scheme that is highly robust with respect to a large spectrum of image processing operations. After performing a two level decomposition of the cover image, the authors embed the first watermark in the LL2 band, and the second watermark in the HH2 band. According to their experimental results, embedding in the LL2 band is more resistant to JPEG compression, wiener filtering, Gaussian noise, scaling, and cropping while embedding in the HH2 band is more resistant to histogram equalization, intensity adjustment, and gamma correction. Nevertheless, the implementation of the idea is seriously flawed. Without taking into consideration the difference in magnitudes of lower and higher DWT coefficients, the scheme is implemented with a scaling factor of 0.1 for both bands. This leads to highly visible degradation in all parts of the image, especially in low frequency areas such as the wall, causing two major detriments: the commercial value of the image is reduced, and a clue is provided to the hacker for unauthorized removal of the watermark.

In, the idea is generalized by embedding the same watermark in all four bands using first and second level decompositions. The watermark embedded in the largest DWT coefficients is robust against JPEG compression, low pass filtering, Gaussian noise, rescaling, rotation, cropping, pixelation, and sharpening, and the watermark embedded in the smallest DWT coefficients is robust against histogram equalization, intensity adjustment, and gamma correction. In the implementation of the scheme, the scaling factor is larger for the lower frequency band, not causing any visible distortion in the watermarked image.

In a semi-blind watermarking scheme, a binary logo is embedded in color images in the DFT domain. After computing the DFT of the cover image, the magnitudes of DFT coefficients are compared, and modified. The given watermark is embedded in three frequency bands: low, middle, and high. The experiments show that the watermarks extracted from the lower frequencies have the best visual quality for low pass filtering, Gaussian noise, JPEG compression, resizing, rotation, and scaling, and the watermarks extracted from the higher frequencies have the best visual quality for cropping, intensity adjustment, histogram equalization, and gamma correction. Extractions from the fragmented and translated image are identical to extractions from the unattacked watermarked image. The collusion and rewatermarking attacks do not provide the hacker with useful tools.

Emergence of New Kingdom Literature - PUZZLE., HISTORICAL BACKGROUND., COPIED FROM THE MIDDLE KINGDOM., ORIGINAL COMPOSITIONS., HISTORICAL WRITING., AUTOBIOGRAPHIES., HYMNS., TWO LANGUAGES. [next] [back] Emancipation Proclamation

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or