Peter H. W. Wong

Novel blind multiple watermarking technique for images

Three novel blind watermarking techniques are proposed to embed watermarks into digital images for different purposes. The watermarks are designed to be decoded or detected without the original images. The first one, called single watermark embedding (SWE), is used to embed a watermark bit sequence into digital images using two secret keys. The second technique, called multiple watermark embedding (MWE), extends SWE to embed multiple watermarks simultaneously in the same watermark space while minimizing the watermark (distortion) energy. The third technique, called iterative watermark embedding (IWE), embeds watermarks into JPEG-compressed images. The iterative approach of IWE can prevent the potential removal of a watermark in the JPEG recompression process. Experimental results show that embedded watermarks using the proposed techniques can give good image quality and are robust in varying degree to JPEG compression, low-pass filtering, noise contamination, and print-and-scan.

Adaptive Chosen-Ciphertext Attack on Secure Arithmetic Coding

The paper ldquosecure arithmetic codingrdquo (in IEEE Transactions on Signal Processing, vol. 55, no. 5, pp. 2263-2272, May 2007) presented a novel encryption scheme called the secure arithmetic coding (SAC) based on the interval splitting arithmetic coding (ISAC) and a series of permutations. In the current work, we study the security of the SAC under an adaptive chosen-ciphertext attack. It is shown that the key vectors used in the codeword permutation step can be recovered with complexity O(N), where N is the symbol sequence length. After getting these key vectors, we can remove the codeword permutation step, and the resulting system has already been shown to be insecure in the original paper. This implies that the SAC is not suitable for the applications where the attacker can have access to the decoder. In addition, we discuss a method to jointly enhance the security and the performance of the SAC.

A capacity estimation technique for JPEG-to-JPEG image watermarking

In JPEG-to-JPEG image watermarking (J2J), the input is a JPEG image file. After watermark embedding, the image is JPEG-compressed such that the output file is also a JPEG file. We use the human visual system (HVS) model to estimate the J2J data hiding capacity of JPEG images, or the maximum number of bits that can be embedded in JPEG-compressed images. A.B. Watsons HVS model (Proc. SPIE Human Vision, Visual Process., and Digital Display IV, p.202-16, 1993) is modified to estimate the just noticeable difference (JND) for DCT coefficients. The number of modifications to DCT coefficients is limited by JND in order to guarantee the invisibility of the watermark. Our capacity estimation method does not assume any specific watermarking method and thus would apply to any watermarking method in the J2J framework.

Highly Parallel Rate-Distortion Optimized Intra-Mode Decision on Multicore Graphics Processors

Rate-distortion (RD)-based mode selections are important techniques in video coding. In these methods, an encoder may compute the RD costs for all the possible coding modes, and select the one which achieves the best trade-off between encoding rate and compression distortion. Previous papers have demonstrated that RD-based mode selections can lead to significant improvements in coding efficiency. RD-based mode selections, however, would incur considerable increases in encoding complexity, since these methods require computing the RD costs for numerous candidate coding modes. In this paper, we consider the scenario where software-based video encoding is performed on personal computers or game consoles, and investigate how multicore graphics processing units (GPUs) may be efficiently utilized to undertake the task of RD optimized intra-prediction mode selections in audio and video coding standards and H.264 video encoding. Achieving efficient GPU-based intra-mode decisions, however, could be nontrivial for two reasons. First, intra-mode decision tends to be sequential. Specifically, the mode decision of the current block would depend on the reconstructed data of the neighboring blocks. Therefore, the coding modes of neighboring blocks would need to be computed first before that of the current block can be determined. This dependency poses challenges to GPU-based computation, which relies heavily on parallel data processing to achieve superior speedups. Second, RD-based intra-mode decision may require conditional branchings to determine the encoding bit-rate, and these branching operations may incur substantial performance penalties when being executed on GPUs due to pipeline architectural designs. To address these issues, we analyze the data dependency in intra-mode decision, and propose novel greedy-based encoding orders to achieve highly parallel processing of data blocks. We also prove that the proposed greedy-based orders are optimal in our problem, i.e., they require the minimum number of iterations to process a video frame given the dependency constraints. In addition, we propose a method to estimate the coding rate suitable for GPU implementation. Experimental results suggest our proposed solution can be more than 50 times faster than the previously proposed parallel intra-prediction, since our work can efficiently exploit the massive parallel opportunity in GPUs.

Block based parallel motion estimation using programmable graphics hardware

In this paper, we propose a graphics processing unit (GPU)-based motion estimation for H.264/AVC by rearranging the encoding order of 4times4 blocks. Previous research by Kelly and Kokaram (2003) and Lin et al. (2006) assume no dependency among adjacent blocks, which is not true for H.264/AVC. The proposed method not only overcomes the dependency problem, but also can be used for both full search and fast search. Experimental results show that our implementation is forty five faster than our SDVTD optimized CPU implementation.

Image characteristic oriented tone mapping for high dynamic range images

This paper presents a novel and efficient tone mapping algorithm for converting high dynamic range (HDR) images back to low dynamic range (LDR) images for displaying purpose because of the limited contrast ratio of common displays and printers. As the ratio between the maximum and minimum values of common HDR images is always very large and also the population usually deflects to one side, for convenient processing, most researchers first take the logarithm on the luminance layer or use another adaptive mapping to shorter the range of the distribution in their tone mapping methods. However, these mappings have already distorted the original imagespsila characteristics. In this paper, there is no such adverse mapping applied on the luminance layer in the proposed tone mapping algorithm. The paper does produce a tone reproduction curve to convert HDR images to LDR images. Adaptive techniques are also manipulated to provide better visual quality. The whole process is automatic and no parameter is required for manual input. The result will be a superior visual quality tone mapped LDR image with original HDR imagepsilas characteristics.

Data hiding and watermarking in JPEG-compressed domain by DC coefficient modification

JPEG is a common image format in the WWW and can potentially be used to hide data for secure internet communication and watermark for copyright control. In this paper, we propose an algorithm to embed the secret or watermark information. The proposed algorithm, named Watermarking by DC Coefficients Modification (WDCM), assumes that the quality factor used in JPEG compression is known. We observe that it is perceptually undetectable if the DC coefficients in certain texture-rich blocks are modified by a small amount. We thus embed the secret information as a binary bit sequence in the quantized DC coefficients in those texture rich blocks. The watermark embedding process can be applied in compression domain without re-encode the data. The information bits are randomized by some pseudo-random noise (PN) sequences, the keys of which are needed for the decoding of the secret information. By embedding the information in the DC components, the proposed algorithm is robust to common JPEG compression if the quality factor is known.

Fast multi-block selection for H.264 video coding

The JVT/H.264 is the new video coding standard which achieves higher coding efficiency than previous standards such as H.263 or MPEG-2. The improvement in the rate-distortion performance in H.264 is mainly due to accurate motion estimation with different mode decision including multiple block size and multiple reference frame motion estimation. However, full exhaustive search of all block sizes is computational intensive with complexity increasing linearly with the number of allowed block size. In this paper, a fast multi-block motion estimation (FMBME) is proposed for H.264 video coding. Experimental results show that the proposed FMBME can efficiently reduce the computational cost by 58% with similar visual quality and bit rate.

A blind watermarking technique in JPEG compressed domain

We propose a blind watermarking technique to embed a watermark in the JPEG compressed domain. Low frequency DCT coefficients are extracted to form an M-dimensional vector. Watermarking is achieved by modifying this vector in order to point to the centroid of a particular cell. This cell is determined according to the extracted vector, private keys and the watermark. A dual-key system is used to reduce the chance of the removal of watermark. An iterative approach is used to prevent the removal of the watermark by JPEG re-quantization. Experimental results show that the watermark can be detected when the watermarked image is further compressed using a larger scaling factor.

Bit-depth expansion by adaptive filter

Bit-depth expansion is important for displaying a low bit-depth image in a high bit-depth monitor. Existing methods tend to give disturbing contouring or blurring artifacts. In this paper, we propose a novel, simple and efficient adaptive method to increase bit-depth taking advantage of the existing techniques to give superior image quality.