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Standards Compliant Watermarking for Access Management Viresh Ratnakar & Onur G.Gulyeruz Please view in full screen presentation mode to see the animations.
Visible Watermarks for Digital Images: Traditional Schemes—Logos An identifying logo in a corner
Visible Watermarks for Digital Images: Traditional Schemes—Blended Marks Unobtrusive visible watermarks aimed at asserting ownership or authenticity
Obtrusive watermarks that can be removed • Similar to scrambling, except that only parts of the image (located on a distinctive pattern) are modified • Example application: user retrieves a watermarked image over the net, pays $$ to print, the printing driver removes the watermark just for printing • Simple for un-lossy-compressed images: Y = X R
Scrambler S E Key K Watermarked JPEG Image JPEG Image D DeScrambler Desired scrambling and descrambling pipeline for compressed images
Format compliance, compression • The XOR idea does not survive lossy JPEG compression • The watermarked image should be format compliant, i.e., in JPEG format • For such completely removable watermarks on JPEG images, we must work with and modify quantized DCT coefficients, not pixels • The size of the watermarked image, ideally, should be no more than the original • We achieve all these goals with the proposed algorithm, DctDots
F1,0 F1,1 F1,2 F1,3 F0,0 F0,1 F0,4 F0,5 F0,2 F0,3 F0,6 F0,7 Cb (Chrominance) F0,40 F0,41 F0,44 F0,45 F0,42 F0,43 F0,46 F0,47 F2,0 F2,1 F2,2 F2,3 Y (Luminance) Cr (Chrominance) DctDots: Apply corruption to the blocks which lie on the pattern
DctDots: Four “tricks” for corrupting blocks • AC Masks: XOR the AC coefficient magnitude bits • AC Swaps: Swap AC coefficient blocks • DC Shuffles: Shuffle DC differentials within • contiguous pattern blocks • DC Bit Shuffles: Shuffle DC differentials within • contiguous pattern blocks
1. AC Masks AC coefficients are coded as Bits in H are the Huffman code for (run = R, magnitude-category = S), Bits in V are the S magnitude bits (1’s complement) We apply XOR (with a keyed PRNG) to just the bits in V, thus maintaining format-compliance and ensuring that the size is not changed H V
2. AC Swaps • Within a color component, entire blocks of AC coefficients (i.e., the 63 coefficients excluding the DC) can be swapped across blocks lying on the pattern. • The swapping is determined by the PRNG, hence reversible. • Format compliant • Size does not increase
3. DC Shuffles • Quantized DC coefficients are differentially coded, hence tricky • Work with consecutive sequences of blocks to be modified (i.e., on the pattern)
3. DC Shuffles – Contd. • Shuffle the differntial quantized DC values within such a pink sequence • Size does not increase at all • The last block in the sequence undergoes no change to its DC value (thus, include the first white block after the pink sequence in the shuffling)
4. DC Bit Shuffles • This step supplements the DC shuffling step—it also works with the differential DC values from the pink blocks • In this step, we go down to the bit planes of the differential DC term
X 1 0 0 1 1 0 1 0 0 X X X X 0 0 1 1 1 1 X X X X X 0 0 0 0 1 X X X X X 1 0 1 1 0 X X X 0 1 0 0 0 0 0 X X 0 0 1 0 0 0 1 1 X X X X X X X X X X X 0 1 1 1 1 0 1 0 0 X X 1 1 0 0 1 0 0 0 4. DC Bit Shuffles – Contd. Bit Plane Blocks
Conclusion • Different goals compared to traditional visible watermarking • DctDots: Format compliant watermarking technique for obtrusive, visible, removable watermarks on JPEG images • Compressed size is exactly the same • Extension to video—only in restricted cases.