Adaptive downsampling to improve image compression at low bit rates.

At low bit rates, better coding quality can be achieved by downsampling the image prior to compression and estimating the missing portion after decompression. This paper presents a new algorithm in such a paradigm, based on the adaptive decision of appropriate downsampling directions/ratios and quantization steps, in order to achieve higher coding quality with low bit rates with the consideration of local visual significance. The full-resolution image can be restored from the DCT coefficients of the downsampled pixels so that the spatial interpolation required otherwise is avoided. The proposed algorithm significantly raises the critical bit rate to approximately 1.2 bpp, from 0.15-0.41 bpp in the existing downsample-prior-to-JPEG schemes and, therefore, outperforms the standard JPEG method in a much wider bit-rate scope. The experiments have demonstrated better PSNR improvement over the existing techniques before the critical bit rate. In addition, the adaptive mode decision not only makes the critical bit rate less image-independent, but also automates the switching coders in variable bit-rate applications, since the algorithm turns to the standard JPEG method whenever it is necessary at higher bit rates.     

A reversible data hiding scheme for VQ indices using locally adaptive coding

Data hiding is designed to solve the problem of secure information exchange through public networks such as Internet. In this paper, we present an improved reversible data hiding scheme that can recover original VQ indices after data extraction. As with Chang et al.’s scheme, our proposed scheme also depends on the locally adaptive coding scheme. However, experimental results confirm that the hiding capacity of our proposed scheme is around 1.36 bpi in most digital images, which is typically higher than that of Chang et al.’s [17]. Moreover, the average compression rate that can be achieved with our proposed scheme is 0.49 bpp, which outperforms both Lin and Chang’s scheme (0.50 bpp), Tsai (0.50 bpp), Chang et al.’s scheme (0.53 bpp), and Yang and Lin’s scheme (0.53 bpp).     

New simple and efficient color space transformations for lossless image compression

We present simple color space transformations for lossless image compression and compare them with established transformations including RCT, YCoCg-R and with the optimal KLT for 3 sets of test images and for significantly different compression algorithms: JPEG-LS, JPEG2000 and JPEG XR. One of the transformations, RDgDb, which requires just 2 integer subtractions per image pixel, on average results in the best ratios for JPEG2000 and JPEG XR, while for a specific set or in case of JPEG-LS its compression ratios are either the best or within 0.1 bpp from the best. The overall best ratios were obtained with JPEG-LS and the modular-arithmetic variant of RDgDb (mRDgDb). Another transformation (LDgEb), based on analog transformations in human vision system, is with respect to complexity and average ratios better than RCT and YCoCg-R, although worse than RDgDb; for one of the sets it obtains the best ratios.     

A reversible steganographic scheme for VQ indices based on locally adaptive coding

Achieving a high embedding capacity and low compression rate with a reversible data hiding method in the vector quantization (VQ) compressed domain is a technically challenging problem. This paper proposes a novel reversible steganographic scheme for VQ compressed images based on a locally adaptive data compression method. The proposed method embeds n secret bits into one VQ index of an index table in Hilbert-curve scan order. The experimental results show that the proposed method can achieve the different average embedding rates of 0.99, 1.68, 2.28, and 3.04 bit per index (bpi) and average compression rates of 0.45, 0.46, 0.5, and 0.56 bit per pixel (bpp) for n = 1, 2, 3, and 4, respectively. These results indicate that the proposed scheme is superior to Chang et al.’s scheme 1 [19], Yang and Lin’s scheme [21], and Chang et al.’s scheme 2 [24].     

Fuzzy quantization based bit transform for low bit-resolution motion estimation

This study proposes a novel fuzzy quantization based bit transform for low bit-resolution motion estimation. We formalize the procedure of bit resolution reduction by two successive steps, namely interval partitioning and interval mapping. The former is a many-to-one mapping which determines motion estimation performance, while the latter is a one-to-one mapping. To gain a reasonable interval partitioning, we propose a non-uniform quantization method to compute coarse thresholds. They are then refined by using a membership function to solve the mismatch of pixel values near threshold caused by camera noise, coding distortion, etc. Afterwards, we discuss that the sum of absolute difference (SAD) is one of the fast matching metrics suitable for low bit-resolution motion estimation in the sense of mean squared errors. A fuzzy quantization based low bit-resolution motion estimation algorithm is consequently proposed. Our algorithm not only can be directly employed in video codecs, but also be applied to other fast or complexity scalable motion estimation algorithms. Extensive experimental results show that the proposed algorithm can always achieve good motion estimation performances for video sequences with various characteristics. Compared with one-bit transform, multi-thresholding two-bit transform, and adaptive quantization based two-bit transform, our bit transform separately gains 0.98 dB, 0.42 dB, and 0.24 dB improvement in terms of average peak signal-to-noise ratio, with less computational cost as well.     

Performance analysis,parameter selection and extensions to H.264/AVC FRExt for high resolution video coding

H.264/AVC FRExt (Fidelity Range Extensions) and Motion JPEG 2000 are the current respective inter-frame and intra-frame coding standards for high resolution (HR) (e.g., 4096 × 2160) visual signals. It is commonly believed that an inter-frame method could achieve higher coding efficiency compared with an intra-frame one, due to the exploitation of video temporal redundancy. However, Motion JPEG 2000 has been selected as the digital cinema compression standard, and some existing work has demonstrated that JPEG 2000 is more suitable at HR situations. In this paper, we compare the rate–distortion (R–D) performance of these two different schemes and give more insight from both theoretical and experimental point of view. We derive an entropy-based R–D model to analyze the test results and the impact of residual entropy and quantization for inter-frame coding. Several extensions are introduced into H.264/AVC FRExt for HR video content for better performance. Experimental results show that these extensions lead to significantly higher coding efficiency and make our extended version more suitable for HR video coding     

20 Gb/s WDM-OFDM-PON over 20-km single fiber uplink transmission using optical millimeter-wave signal seeding with rate adaptive bit-power loading

We experimentally demonstrate the use of millimeter-wave signal generation by optical carrier suppression (OCS) method using single-drive Mach–Zehnder modulator as a light sources seed for 20 Gb/s WDM-OFDM-PON in 20-km single fiber loopback transmission based on cost-effective RSOA modulation. Practical discrete rate adaptive bit loading algorithm was employed in this colorless ONU system to maximize the achievable bit rate for an average bit error rate (BER) below 2 × 10⁻³.     

Performance evaluation of the fractional wavelet filter: A low-memory image wavelet transform for multimedia sensor networks

Existing image wavelet transform techniques exceed the computational and memory resources of low-complexity wireless sensor nodes. In order to enable multimedia wireless sensors to use image wavelet transforms techniques to pre-process collected image sensor data, we introduce the fractional wavelet filter. The fractional wavelet filter computes the wavelet transform of a 256 × 256 grayscale image using only 16-bit fixed-point arithmetic on a micro-controller with less than 1.5 kbyte of RAM. We comprehensively evaluate the resource requirements (RAM, computational complexity, computing time) as well as image quality of the fractional wavelet filter. We find that the fractional wavelet transform computed with fixed-point arithmetic gives typically negligible degradations in image quality. We also find that combining the fractional wavelet filter with a customized wavelet-based image coding system achieves image compression competitive to the JPEG2000 standard.     

JPEG2000小波变换器的VLSI结构设计

新一代静止图像压缩标准JPEG2000将离散小波变换(DWT)作为其核心变换技术,并推荐采用推举体制(lifting)快速算法来实现.空间组合推举体制算法(SCLA)大大降低了lifting的运算量.当选用9/7小波滤波器时,SCLA的乘法运算量只有lifting的7/12.本文提出了一种实现SCLA算法的VLSI结构,降低了基于lifting实现的运算量, 加快了变换的速度,减小了电路的规模.本文的二维正反小波变换器已经作为单独的IP核应用于我们目前正在开发的JPEG2000图像编解码芯片中.     

一种基于噪声模型的小波系数量化补偿方法

本文提出一种基于噪声模型的小波系数量化补偿方法,在小波变换域上对零截断系数采用简单的噪声模型进行补偿,解码端根据模型参数,合成随机纹理,改善因系数零截断量化造成的随机纹理失真,从而提高解码图像的主观视觉质量.实验结果表明,模型参数编码只需0.013bpp.在相同编码比特率的情况下,与JPEG2000缺省编码方法相比,图像主观质量得到很大改善.     

A planar waveguide optical discrete Fourier transformer design for 160 Gb/s all-optical OFDM systems

A cost-effective all-optical discrete Fourier transformer (ODFT) is designed based on a silicon planar lightwave circuit (PLC), which can be applied to all-optical orthogonal frequency division multiplexing (OFDM) transmission systems and can be achieved by current techniques. It consists of 2 × 2 directional couplers, phase shifters and optical delay lines. Metal-film heaters are used as phase shifters, according to the thermooptic effect of SiO₂. Based on the ODFT, a 160 Gb/s OFDM system is set up. Simulation results show excellent bit error rate (BER) and optical signal-to-noise ratio (OSNR) performances after 400 km transmission.     

A PAPR reduction technique using Hadamard transform combined with clipping and filtering based on DCT/IDCT for IM/DD optical OFDM systems

In Intensity Modulator/Direct Detection (IM/DD) optical OFDM systems, the high peak-to-power average ratio (PAPR) will cause signal impairments through the nonlinearity of modulator and fiber. In this paper, a joint PAPR reduction technique based on Hadamard transformation and clipping and filtering using DCT/IDCT transform has been proposed for mitigating the impairments in IM/DD optical OFDM system. We then experimentally evaluated the effect of PAPR reduction on the bit error rate (BER) performance and the results show the effectiveness of the proposed technique. At a bit error rate (BER) of 1 × 10⁻³, the receiver sensitivity of the proposed 2.5 Gb/s IM/DD optical OFDM system after 100-km standard single-mode fiber transmission has been improved by 0.8 dB, 1.3 dB and 3.1 dB for a launch power of 6.4 dBm, 8 dBm and 10 dBm respectively when compared with the classical system.     

Improving energy efficiency using a link adaptation algorithm dedicated for 100 Gbps wireless communication

This paper presents a link adaptation algorithm dedicated for 100 Gbps wireless transmission. Interleaved Reed-Solomon codes are selected as forward error correction (FEC) algorithms. The redundancy of the codes is selected according to the channel bit error rate (BER). The uncomplicated FEC scheme allows implementing a complete data link layer processor in an FPGA (field programmable gate array). In our case, we use the Virtex7 FPGA to validate the functionality of our implementation. The proposed FPGA-processor achieves 169 Gbps throughput. Moreover, the implementation is synthesized into 40 nm CMOS technology and the described link adaptation algorithm allows reducing consumed energy per bit to values below 1 pJ/bit at BER <1e−4. With higher BER, the energy increases up to ∼13 pJ/bit.     

Correlation based universal image/video coding loss recovery

Coding artifacts are annoying in highly compressed signals. Most of the existing artifact reduction methods are designed for one specific type of artifacts, codecs, and bitrates, which are complex and exclusive for one type of artifact reduction. Since both the compressed image/video and the coding error contain information of the original signal, they are highly correlated. Therefore, we try to recover some lost data based on the correlation between the compressed signal and the coding error, and introduce a novel and universal artifact reduction method. Firstly, according to the spatial correlation among pixels, a pixel-adaptive anisotropic filter is designed to reconstruct the distorted signal. Next, a globally optimal filter is designed to further recover the coding loss. Experimental results demonstrate that within an extensive range of bitrates, the proposed method achieves about 0.8 dB, 0.45 dB, 0.3 dB, and 0.2 dB on average of PSNR improvement for JPEG, MPEG4, H.264/AVC, and HEVC compressed signals, respectively.     

Synthesis,photoluminescence and electroluminescence properties of iridium complexes with bulky carbazole dendrons

We synthesized solution-processable iridium complexes having bulky carbazole dendrons, fac-tris[2-{3-(3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl)Phenyl)pyridine]iridium (III) (mCP)₃Ir and fac-bis[2-{3-(3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl)phenyl}pyridine][2-{3-(3,5-di(4-pyridyl)phenyl)phenyl}pyridine]iridium (III) (mCP)₂(bpp)Ir. Photoluminescence quantum efficiencies (PLQEs) of (mCP)₃Ir and (mCP)₂(bpp)Ir in their diluted solutions were 91% and 84%, respectively. They showed high PLQEs of 49% for (mCP)₃Ir and 29% for (mCP)₂(bpp)Ir even in a neat film. The triplet exciton energy level of the dendronized ligand (2.8 eV), 2-[3-{3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl}]pyridine 10, and the dendron (2.9 eV), 3,5-bis(3,6-di-n-butylcarbazol-9-yl)benzene 7, are enough higher than that of the core complex Ir(ppy)₃ (2.6 eV). External quantum efficiency (EQE) of single layer light-emitting device with (mCP)₂(bpp)Ir was much higher than that of (mCP)₃Ir because of better affinity of (mCP)₂(bpp)Ir to cathode metal. When an electron transporting and hole-blocking material was used, the EQEs of double layer devices were dramatically improved to 8.3% for (mCP)₃Ir and 5.4% for (mCP)₂(bpp)Ir at 100 cd/m².     

Image coding using dual-tree discrete wavelet transform

In this paper, we explore the application of 2-D dual-tree discrete wavelet transform (DDWT), which is a directional and redundant transform, for image coding. Three methods for sparsifying DDWT coefficients, i.e., matching pursuit, basis pursuit, and noise shaping, are compared. We found that noise shaping achieves the best nonlinear approximation efficiency with the lowest computational complexity. The interscale, intersubband, and intrasubband dependency among the DDWT coefficients are analyzed. Three subband coding methods, i.e., SPIHT, EBCOT, and TCE, are evaluated for coding DDWT coefficients. Experimental results show that TCE has the best performance. In spite of the redundancy of the transform, our DDWT _ TCE scheme outperforms JPEG2000 up to 0.70 dB at low bit rates and is comparable to JPEG2000 at high bit rates. The DDWT _TCE scheme also outperforms two other image coders that are based on directional filter banks. To further improve coding efficiency, we extend the DDWT to an anisotropic dual-tree discrete wavelet packets (ADDWP), which incorporates adaptive and anisotropic decomposition into DDWT. The ADDWP subbands are coded with TCE coder. Experimental results show that ADDWP _ TCE provides up to 1.47 dB improvement over the DDWT _TCE scheme, outperforming JPEG2000 up to 2.00 dB. Reconstructed images of our coding schemes are visually more appealing compared with DWT-based coding schemes thanks to the directionality of wavelets.     

All-digital controlled boost DC–DC converter with all-digital DLL-based calibration

Traditional digital controls mostly use digital–analog converters to convert input and output voltages into digital coding to achieve control. This paper proposes the use of two digital ramps with two different frequencies to replace a digital–analog converter. This approach can produce seven bit resolution for the DPMW signal. In addition, we use an all-digital DLL phase correction concept to further enhance the resolution of the DPWM signal by an additional three bits, resulting in 10-bit DPWM signal resolution. The proposed circuit uses 0.35 μm CMOS processes, with a core area of 0.987 mm², a system switching frequency of 500 KHz, an input voltage range of 3.3–4.2 V, and an output voltage range of 5 V. Output voltage measurement accuracy reaches 99%, while the system reaches efficiency of 91% with output loads of up to 500 mA.     

A novel high-performance reversible data hiding scheme using SMVQ and improved locally adaptive coding method

Reversible data hiding is a method that not only embeds secret data but also reconstructs the original cover image without distortion after the confidential data are extracted. In this paper, we propose novel reversible data hiding scheme that can embed high capacity of secret bits and recover image after data extraction. Our proposed scheme depends on the locally adaptive coding scheme (LAC) as Chang&Nguyen’s scheme and SMVQ scheme. Experimental results show that the compression rate of our proposed scheme is 0.33 bpp on average. To embed secret bits we propose the normal-hiding scheme and the over-hiding scheme which have an average embedding rate of 2.01 bpi and 3.01 bpi, more than that of Chang&Nguyen’s scheme (1.36 bpi). The normal-hiding scheme and the over-hiding scheme also has high embedding efficiency of 0.28 and 0.36 on average, which are better than that of Chang&Kieu’s scheme (0.12), Chang&Nguyen’s scheme (0.18) and Chang&Nguyen’s scheme (0.16).     

All-printed and highly stable organic resistive switching device based on graphene quantum dots and polyvinylpyrrolidone composite

We propose all printed and highly stable organic resistive switching device (ORSD) based on graphene quantum dots (G-QDs) and polyvinylpyrrolidone (PVP) composite for non-volatile memory applications. It is fabricated by sandwiching G-QDs/PVP composite between top and bottom silver (Ag) electrodes on a flexible substrate polyethylene terephthalate (PET) at ambient conditions through a cost effective and eco-friendly electro-hydrodynamic (EHD) technique. Thickness of the active layer is measured around 97 nm. The proposed ORSD is fabricated in a 3 × 3 crossbar array. It operates switching between high resistance state (HRS) and low resistance state (LRS) with OFF/ON ratio ∼14 for more than 500 endurance cycles, and retention time for more than 30 days. The switching voltage for set/reset of the devices is ±1.8 V and the bendability down to 8 mm diameter for 1000 cycles are tested. The elemental composition and surface morphology are characterized by XPS, FE-SEM, and microscope.     

Pseudo-V2 control with adaptive compensation for fast-transient current-mode buck converter

A type of pseudo-V² control, with on-chip adaptive compensation to achieve fast transient (FT) response for current mode DC–DC buck converter, has been proposed and simulated using 0.18 μm CMOS technology in this paper. Based on a new on-chip capacitor multiplier, adaptive compensation is achieved by making the compensation capacitance to track the load current. The proposed pseudo-V² control utilizes the output ripple to determine the duty cycle during load transient. Thus the overshoot/undershoot voltage and the transient recovery time are effectively reduced. Simulation results demonstrate the transient ripple is smaller than 50 mV and the transient recovery time is shorter than 10 μs for a 450 mA load current step. The maximum power conversion efficiency is 94.6% at 1 MHz switching frequency when input and output voltages are 5 V and 1.8 V, respectively.