Browsing by Author "Tang, CW"

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A feature-based robust digital image watermarking scheme
(2003-04-01)
Tang, CW
;
Hang, HM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A robust digital image watermarking scheme that combines image feature extraction and image normalization is proposed. The goal is to resist both geometric distortion and signal processing attacks. We adopt a feature extraction method called Mexican Hat wavelet scale interaction. The extracted feature points can survive a variety of attacks and be used as reference points for both watermark embedding and detection. The normalized image of an image (object) is nearly invariant with respect to rotations. As a result, the watermark detection task can be much simplified when it is applied to the normalized image. However, because image normalization is sensitive to image local variation, we apply image normalization to nonoverlapped image disks separately. The disks are centered at the extracted feature points. Several copies of a 16-bit watermark sequence are embedded in the original image to improve the robustness of watermarks. Simulation results show that our scheme can survive low-quality JPEG compression, color reduction, sharpening, Gaussian filtering, median filtering, row or column removal, shearing, rotation, local warping, cropping, and linear geometric transformations.
A novel visual distortion sensitivity analysis for video encoder bit allocation
(2004)
Tang, CW
;
Chen, CH
;
Yu, YH
;
Tsai, CJ
;
資訊工程學系
A novel video bit allocation technique adopting a visual distortion sensitivity model for better rate-visual distortion coding control is proposed in this paper. Instead of applying complicated semantic understanding, the proposed automatic distortion sensitivity analysis process analyzes both the motion and the texture structures in the video sequences in order to achieve better bit allocation for rate-constrained video coding This analysis evaluates the tolerable perceptual distortions on a macroblock basis, and allocates fewer bits to regions permitting large perceptual distortions for rate reduction. The proposed algorithm can be incorporated into any existing video coding rate control schemes to achieve same Visual quality at greatly reduced bitrate. Experiments based on H.264 show that this technique achieves bit-rate saving of up to 40% with no perceptual quality degradations. The experiments also demonstrate the inadequacy Of using PSNR as a distortion measure in a video coding framework.
Adaptive rate-distortion optimization using perceptual hints
(2004)
Tsai, CJ
;
Tang, CW
;
Chen, CH
;
Yu, YH
;
資訊工程學系
A novel video coding approach that performs adaptive rate-distortion optimization guided by perceptual hints is proposed in this paper The key idea is to adaptively adjust the Lagrange multipliers of the RDO coder control module based on visual attention analysis. The observation is that human vision is sensitive to movement of well structured objects while tolerates large distortion in moving areas with random structure (texture-wise and motion-wise). The proposed algorithm analyzes permissible perceptual distortions and, accordingly, assigns larger Lagrange multipliers to regions that are perceptually less sensitive to distortion so that rate-reduction is weighted more than distortion reduction in these regions. Experiments show that this scheme achieves bit-rate saving of 5-7% with virtually same perceptual quality and is very promising for practical systems.
An image feature based robust digital watermarking scheme
(2002)
Tang, CW
;
Hang, HM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A novel robust digital image watermarking scheme which combines image feature extraction and image normalization is proposed. The goal is to resist both geometrical and signal processing attacks. We adopt a feature extraction method called Mexican Hat wavelet scale interaction. The extracted feature points can survive various attacks such as common signal processing, JPEG compression, and geometric distortions. Thus, these feature points can be used as reference points for both watermark embedding, and detection. The normalized image of a rotated image (object) is the same as the normalized version of the original image. As a result, the watermark detection task can be much simplified when it is done on the normalized image without referencing to the original image. However, because image normalization is sensitive to image local variation, we apply image normalization to non-overlapped image disks separately. The center of each disk is an extracted feature point. Several copies of one 16-bit watermark sequence are embedded in the original image to improve the robustness of watermarks. Simulation results show that our scheme can survive low quality JPEG compression, color reduction, sharpening, Gaussian filtering, median filtering, printing and scanning process, row or column removal, shearing rotation, scaling, local warping, cropping, and linear transformation.
Broadband, planar, doubly balanced star mixers
(2000)
Chang, CY
;
Tang, CW
;
Niu, DC
;
電信工程研究所
;
Institute of Communications Engineering
Planar broadband star mixers comprising two CPW-CPS T-junction dual baluns are developed. The bandwidth is about 6:1 without treatment of even mode resonance. After improving of even-mode resonance, the measured relative bandwidths of the star mixers can be larger than 15:1. The planar structure of the circuit is suitable for both MIC and MMIC fabrication. Some MIC prototype circuits are fabricated with Al2O3 substrate. The measured conversion losses of the star mixers are about 6 to 10 dB typically within the bandwidth.
Efficient algorithms in determining JPEG-effective watermark coefficients
(2004)
Tang, CW
;
Hang, HM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A set of coefficient selection rules is proposed for efficiently determining the effective DCT watermarking coefficients of an image for JPEG attack. These rules are simple in computation but they are derived from the theoretically optimized data set with the aid of the parametric classifiers. They improve the watermark robustness (correctly decoding) and, in the mean time, decrease the error detection probability (correct detection). The frequency versus watermark strength space is used in constructing the selection rules. Simulation results show that the computational complexity is significantly reduced compared to our previous theory-based optimization work, but still the selected coefficients can achieve nearly the same performance as the original scheme.
Efficient green organic light-emitting diodes with stericly hindered coumarin dopants
(2001-11-26)
Chen, CH
;
Tang, CW
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We have discovered two stericly hindered green coumarin derivatives which showed significantly better thermal stability and overall electroluminescence (EL) performance than those of the corresponding 3-(2-benzothiazolyl)-7-(diethylamino)-2H-1-benzopyran-2-one (C-6) and 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl- 2,3,6,7-tetrahydro-1H,5H,11H-benzo[l]pyrano[6,7, 8-ij] quinolizin-11-one (C-545T). The strategic incorporation of bulky spacer t-butyl groups in these dopants considerably delays the onset of concentration quenching. In particular, 10-[2(5,7-di-t-butyl)benzothiazolyl]-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo-[l]pyrano[6,7,8-ij]quinolizin-11-one (C-545TB) with its superb thermal stability (T-g=142 degreesC; T-d=327 degreesC), high luminance efficiency (similar to 13 cd/A), good Commission Interationale d'Eclairage (CIE) coordinates (x=0.30; y=0.64) and a nearly flat EL efficiency dependence on drive current stands out as one of the best choice of green dopants for use in the passive-matrix organic light-emitting diode displays. (C) 2001 American Institute of Physics.
Exploring effective coefficients in transform-domain perceptual watermarking
(2003)
Tang, CW
;
Hang, HM
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
An image watermark parameter optimization procedure is proposed for selecting the most effective DCT coefficients for watermark embedding. Using this set of coefficients improves the watermark robustness and reliability against attack while it maintains the transparency of the embedded watermark. With the aid of prior knowledge of attacks, the visual masking effect and the attack distortion on each (DCT) transform coefficient are pre-calculated so that a maximum strength watermark within visual threshold can be inserted. There are two stages in the design phase. First, taking into account the combined effect of watermark embedding and attack, we pick up the robust coefficients that resist a specific type of attacks and in the meanwhile we keep the distortion lower than the visual threshold. Although typically the watermark detection reliability increases with the increasing number of embedded coefficients, the less effective coefficients may degrade the overall detection performance. Thus, in the second stage, some initially selected coefficients are discarded by an iterative process to reduce the overall error detection probability. Since digital images are often compressed for efficient storage and transmission, we adopt JPEG compression as the attacking source. The simulation results show that the detection error probability is significantly reduced when the selected robust coefficients are in use. These coefficients with watermark embedded on them can also survive color reduction, Gaussian filtering, and frequency mode Laplacian removal (FMLR) attacks.
LTCC-MLC chip-type balun realised by LC resonance method
(2002-05-23)
Tang, CW
;
Chang, CY
;
電信工程研究所
;
Institute of Communications Engineering
A multilayer ceramic balun designed in the 2.4 GHz ISM band frequency is presented. A multilayer structure to realise the low temperature co-fired ceramic (LTCC) balun is proposed. This type of balun comprises an embedded capacitor and meandered or spiral coupled lines. The use of an LC resonator can shrink the length of a coupled transmission line and can be designed very easily to have various balanced output port impedances. Excellent performance of phase and amplitude balance may be achieved by the proposed method. Measured results of the LTCC-multilayer ceramic (MLC) balun match well with the computer simulation.
Realization of transmission zeros in combline filters using an auxiliary inductively coupled ground plane
(2003-10-01)
Tang, CW
;
Lin, YC
;
Chang, CY
;
電信工程研究所
;
Institute of Communications Engineering
The out-band transmission zeros of the multilayer low-temperature co-fired ceramic bandpass filter are studied in this paper. The design target of this filter, with the passband between 2.3-2.65 GHz (the true application is 2.4-2.483 GHz), is to reject the local oscillator and image signals and, in the mean time, to suppress the harmonic frequency. This filter is a modified three-pole combline filter, which can easily achieve a high rejection rate and low insertion loss. The source-load coupling capacitor incorporation with cross-coupling grounding inductors can generate three transmission zeros. By properly adjusting the inductance values of the inductors between three resonators and ground can easily manipulate the transmission zero at a high-side skirt to suppress the harmonic frequency. The measured results match well with the electromagnetic simulation that evidences the feasibility of the proposed design.
Ultra-broad-band doubly balanced star mixers using planar Mouw's hybrid junction
(2001-06-01)
Chang, CY
;
Tang, CW
;
Niu, DC
;
電信工程研究所
;
Institute of Communications Engineering
Ultra-broad-band star mixers using planar Mouw's hybrid junction [1] are presented in this paper. The planar Mouw's hybrid junction is realized by coplanar waveguide (CPW) to coplanar strip (CPS) or CPW to CPW T-junctions. A new explanation of Mouw's theory based on coupled transmission lines and including the transmission line losses is presented, The modified theory is more suitable for ultra-broad-band mixer design. Some prototype mixers with CPW to CPS or CPW to CPW T-junctions are fabricated with Al2O3 substrate, The prototype mixers show a bandwidth of greater than 20:1 if the even-mode resonance has been damped out. Method for damping out the even-mode resonance is also presented. All of the prototype circuits show much broader bandwidth than that of conventional star mixer.
Using buried capacitor in LTCC-MLC balun
(2002-07-18)
Tang, CW
;
Chang, CY
;
電信工程研究所
;
Institute of Communications Engineering
A novel chip-type ceramic balun designed in the 2.4 GHz ISM band frequency is presented. A buried capacitor is included in the balun, so that the length of the coupled transmission lines can be reduced and can be designed very easily. A meander or spiral broadside coupled-line is adopted to realise the proposed LTCC multi-layer balun. The measured performances of phase and amplitude balance for this LTCC-MLC balun show a good match with computer simulation.
Visual sensitivity guided bit allocation for video coding
(2006-02-01)
Tang, CW
;
Chen, CH
;
Yu, YH
;
Tsai, CJ
;
資訊工程學系
A video bit allocation technique adopting a visual distortion sensitivity model for better rate-visual distortion Coding control is proposed in this paper. Instead of applying complicated semantic understanding, the proposed automatic distortion sensitivity analysis process analyzes both the motion and the texture structures in the video sequences in order to achieve better bit allocation for rate-constrained video coding. The proposed technique evaluates the perceptual distortion sensitivity on a macroblock basis, and allocates fewer bits to regions permitting large perceptual distortions for rate reduction. The proposed algorithm can be incorporated into existing video coding rate control schemes to achieve same visual quality at reduced bitrate. Experiments based on H.264 JM7.6 show that this technique achieves bit-rate saving of up to 40.61%. However, the conducted subjective viewing experiments show that there is no perceptual quality degradation.