Chih-Chang Chen

LED back-light driving system for LCD panels

In this paper, a light emitting diode (LED) back-light driving system for liquid crystal display (LCD) panels is proposed. Due to improvement in luminous efficiency, long life and wide color gamut, LED has gradually substituted for cold cathode fluorescent lamp (CCFL) as back light. In order to compete with other display devices and receive wide acceptance in the commercial arena, back-light driving efficiency, luminous efficiency and LED arrangement need to further improve. In this paper, an LED bypass circuit is proposed to prevent LED arrays from open-circuit, improving back-light reliability and availability significantly. In addition, bi-directional buck+boost converters are adopted to speed up state transition when using a current-type burst-mode dimming control for LED back-light drivers. Moreover, an effective driving circuit for achieving RGB light scan is introduced. Simulated and measured results are presented to verify the feasibility of the proposed driving system.

Automatically-Determined Region of Interest in JPEG 2000

This work presents an automatically-determined region of interest (ROI) scheme embedded in JPEG 2000. The proposed scheme analyzes the image content and then determines the probable ROI masks by examining the significant states of high-frequency subbands generated from embedded block coding with optimized truncation (EBCOT). Additionally, probable ROI masks are constructed in all bit planes of subbands by categorizing sub-blocks as either interesting or uninteresting, smoothing subblocks of interest, and grouping these subblocks based on an or no initial point. The rate-distortion (RD) pairs corresponding to all probable ROI masks are then estimated from the RD distribution during the Tier-2 coding process of EBCOT. Based on these estimations, the Lagrangian multiplier method is employed in the RD function to obtain the optimized ROI mask from the probable masks by minimizing the distortion of the ROI-encoded image at a given bit-rate constraint. ROI-encoded images obtained using the proposed scheme outperform ROI-encoded images obtained via the conventional schemes using fixed-square and object-segmentation masks, as judged by subjective visual perception and objective measurement in terms of peak signal-to-noise ratio. Particularly, the proposed scheme can easily adapt the ROI region with varied sizes and shapes according to the bit-rate constraint whereas the conventional schemes only adopt the fixed-square region and fixed segmented objects. Furthermore, when the proposed scheme is applied to motion JPEG 2000 for video compression, the centroid of the ROI mask in the previous frame can be used as an initial point for merging the subblocks of interest in the current frame to track the ROI masks in a video sequence. Therefore, the proposed scheme can easily be employed to improve the perceptual and objective performance in the ROI coding associated with JPEG 2000 and motion JPEG 2000.

Tracking and counting people in visual surveillance systems

The greatest challenge on monitoring characters from a monocular video scene is to track targets under occlusion conditions. In this work, we present a scheme to automatically track and count people in a surveillance system. First, a dynamic background subtraction module is employed to model light variation and then to determine pedestrian objects from a static scene. To identify foreground objects as characters, positions and sizes of foreground regions are treated as decision features. Moreover, the performance to track individuals is improved by using the modified overlap tracker, which investigates the centroid distance between neighboring objects to help on target tracking in occlusion states of merging and splitting. On the experiments of tracking and counting people in three video sequences, the results exhibit that the proposed scheme can improve the averaged detection ratio about 10% as compared to the conventional work.

Sequential Color LED Backlight Driving System for LCD Panels with Area Control

In this paper, a sequential color light emitting diode (LED) backlight driving system for liquid crystal display (LCD) panels with area control is proposed. Due to improvement on luminous efficacy, fast response, long life, mercury free, and wide color gamut, LED has gradually substituted for cold cathode fluorescent lamp (CCFL) as backlight. Although some novel CCFLs with low content of mercury and wide color gamut have been proposed, it is difficult to shorten their on-off transition. Recently, a novel display technique, namely area control, requiring backlights with fast response has been proposed to improve the contrast ratio of LCD and reduce power consumption of the backlights. With the area control, a panel is partitioned into several areas, and the backlight brightness of each area is controlled individually. In addition, color sequential display (CSD) is introduced to further reduce the power consumption. A sequential color LED backlight driving system with area control has been built, from which experimental measurements have verified the feasibility of the proposed driving system.

Region of interest determined by perceptual-quality and rate-distortion optimization in JPEG 2000

The region-of-interest (ROI) coding of Joint Photographic Experts Group (JPEG) 2000 is an important option to encode pictures on a limited bit rate. This work presents a scheme to automatically generate the ROI mask during the encoding process of JPEG 2000. In the proposed scheme, the embedded block coding with optimized truncation (EBCOT) is utilized to provide information of the significant states, rates and distortions at bit-planes for analyzing picture contents, and then determining an appropriate ROI mask that is optimized by the perceptual quality and rate-distortion function. During the bit-plane coding, the coefficients of discrete wavelet transform (DWT) in the magnitude refinement pass of the EBCOT are grouped into the interested or uninterested ones by using their pass scanning results from perceptual point of view. Furthermore, the rate-distortion function is applied to automatically determine the optimized ROI mask from the probable masks that are formed by the interested sub-blocks, according to the required bit rate. As compared to the scheme using the fixed-square or fixed-region ROI mask, the proposed scheme can provide clearer object contours and better image quality. Additionally, the proposed ROI determination scheme can be easily realized and embedded in JPEG 2000 encoding process.

Multiphase multilamp driving system for LCD back light

This work presents a multiphase multilamp driving system for liquid crystal display (LCD) back light The driving system adopts a multiphase inverter to drive cold cathode fluorescent lamps (CCFL) to reduce input current ripple. Furthermore, to prevent current imbalance among lamps a multiphase transformer is introduced in the proposed system. Compared with the conventional single-phase driving system, the proposed one can have the merit of requiring less number of transformers. A three-phase driving system with current balancing transformer has been built, from which experimental results have verified the feasibility of the proposed multiphases driving system.

A low-complexity computation scheme of discrete cosine transform and quantization with adaptation to block contents

In this paper, we propose a low-complexity computation scheme of Discrete Cosine Transform (DCT) and quantization, which is adaptive to block contents of image frames. With consideration of maintaining the quality of the decoded image and reducing the computational complexity, we take a closer look at the relationship between block contents and the quantization table. Based on this relationship to predict the number of DCT coefficients required for calculation, we develop an adaptive scheme to update the DCT calculation structure. Comparing our scheme in deriving DCT coefficients with that of DCT calculation for a fixed number of coefficients. Our scheme can compromise image qualities with computational complexities. In other words, the proposed scheme could adjust the DCT calculation complexity depending on the image contents. The image quality from our scheme is comparable to that of a complete 64-coefficient DCT calculation process. Therefore, our proposed scheme to calculate DCT and quantization, with abilities to reduce the computational complexity and preserve the picture quality, is suitable and applicable in video and image compression used nowadays.

Gender-to-Age hierarchical recognition for speech

In this work, a gender-to-age hierarchical analysis structure is proposed rather than directly classifying speech clips into gender and age categories. A two-stage Support Vector Machine (SVM) classifier is adopted to identify a female and male, and then conduct an age classification. To realize the gender recognition, the mean of the fundamental frequency and the standard deviation of the fast Fourier transform from speech clips are employed. Additionally, a part of 16 extracted speech characteristic parameters are used to understand human ages according to their genders. Notably, human utterance characteristics are considered to determine adequate speech parameters to minimize feature ambiguities among females and males under different ages. The experimental results demonstrate that the proposed gender-to-age hierarchical recognition scheme can achieve 17.9% accuracy-rate improvement in average, as compared to the results from the conventional direct classification scheme.

Effective memory reduction scheme used for reference frames in H.264/AVC video codec

In the H.264/AVC video codec, multiple reference frames are applied for motion estimation to provide good coding efficiency. However, multiple reference frames also require more memory cost than one reference frame used in a video codec. To minimize the amount of memory requirement, this work proposes to add a decision unit in the H.264/AVC codec to store these reference frames. The said decision unit would look closely at macroblock (MB) of the currently decoded frame to determine its storage type to be compressed or reconstructed data, according to the encoding parameters of subblocks in this MB. Furthermore, an adaptive scheme is proposed to store the currently decoded frame as reconstructed picture for lowering the computational complexity and using the buffer in full. Experimental results reveal that the proposed memory reduction scheme requires lower complexity and better picture quality than the conventional work. Therefore, the proposed memory reduction scheme can be widely used in various applications of the H.264/AVC codec to minimize the memory requirement.

Application-Specific Data Path for Highly Efficient Computation of Multistandard Video Codecs

A novel mechanism that flexibly adapts data flows and configures computational units is proposed to establish an application-specific data path in the digital signal processor (DSP) that can efficiently perform multistandard video codecs. Based on this mechanism, the proposed application-specific data path, using the very long instruction word (VLIW) architecture with eight computational units of five arithmetic logic units (ALUs), one multiplier and two load/store units, is designed to perform five adaptive operations according to the characteristics of the low-level functions of MPEG-2, MPEG-4 and H.264/AVC video codecs. Using these adaptive operations, the proposed application-specific data path reduces the number of clock cycles required by the TI TMS320C64x data path to perform the low-level functions of the MPEG-2 video encoder and the H.264/AVC video decoder by 23.10% and 28.43%, respectively, for 30 352times288-pixel Foreman frames. Additionally, considering the operating frequency, the proposed application-specific data path reduces the computation time required by the TI TMS320C64x data path to realize the abovementioned encoder and decoder by 19.86% and 25.41%, respectively. Based on the TSMC 0.18-mum CMOS cell library, the proposed application-specific data path is implemented, and exhibits the highest ratio of computational power to hardware cost among all of the data paths associated with the conventional DSPs in implementing the low-level functions of video codecs