Zhi-Hu Liang

Skin color enhancement based on favorite skin color in HSV color space

Skin color enhancement based on favorite skin color is proposed to make skin color displayed on large screen flat panel TVs agree with human favorite skin color. A robust skin detection method in different intensity is obtained after analyzing the distribution of skin color in HSV color space. The favorite skin color region is found via a psychological experiment too. Then the skin color detected is enhanced with different degrees according to the distance between it and the favorite skin color. The experimental result displayed on 60-inch plasma display panel (PDP) shows that the skin colors detected are approached to the favorite skin color region with different degrees. The skin colors enhanced are more natural and agree with the comprehension of human vision and psychology perceived in advance.

A real-time image processor with combining dynamic contrast ratio enhancement and inverse gamma correction for PDP

Inverse gamma correction must be performed before displaying the received video signal because alternating current plasma display panel (AC PDP) has a linear output luminance response to a digital-valued input. At the same time contrast ratio enhancement is necessary for improving the image quality of display devices. The histogram equalization (HE) is an important contrast ratio enhancement method. But sometimes HE can produce unrealistic effects in images. In this paper, a new method of combining dynamic contrast ratio enhancement and inverse gamma correction for AC PDP is proposed. The dynamic contrast ratio enhancement and the inverse gamma correction are realized simultaneously in the proposed method. Furthermore the over-enhancement caused by the traditional HE can be avoided. A real-time image processor with the proposed method was designed and implemented. Simulations and experimental results on a 50-in. AC PDP show that the image quality of AC PDP can be improved obviously.

Energy Recovery Circuit with Auxiliary Power Supply for AC Plasma Display Panel

A new energy recovery circuit with an auxiliary power supply for AC plasma display panel is proposed, which can provide zero-voltage switching of all switches by rejecting the surge current when sustain switches are turned on. The operation process of the circuit is analyzed, and the results of experiments based on a 12-in PDP panel with 100 kHz sustaining frequency show that the proposed circuit could reduce power losses of energy recovery circuit of AC plasma display panel.

3-dimensional error diffusion method based on edge detection for digital display devices

The conventional error diffusion (CED) method adopted in digital display devices is simply modified from Floyd-Steinberg error diffusion method, which will degrade image quality by introducing nonlinear distortion (worm artifacts), linear distortion (sharpening), noise and the loss of image details. To overcome the shortcomings of the CED method, this paper proposes 3-dimensional (3D) error diffusion method based on edge detection. The proposed method diffuses quantization errors to the neighbor pixels of current frame and the neighbor pixel of the next frame. And the weights of error filters are dynamically adjusted based on the results of edge detection in each pixels processing, which makes the weights coincide with the local edge feathers of input image. Simulation and experimental results show that the 3D error diffusion method can reduce worm artifacts and improve reproduction precision of image details.

An adaptive subfield coding method for driving AC PDPs

The image quality suffers from the lack of grayscale expression capability when the simple accumulation of light emission is applied to express grayscale in alternating current plasma display panels (ac PDP). To solve the problem, an adaptive subfield coding (ASC) method for driving ac PDP is proposed, in which subfield vector is adaptively figured out based on the normalized histogram of input image every television field. The calculated subfield vector can express the most grayscale information of input image. And then the number of sustain pulses in each subfield is adjusted according to the calculated subfield vector. Simulation results show that the proposed method can eliminate the dynamic false contours in ac PDPs and overcome the lack of grayscale expression capability caused by the simple-accumulation-lighting-mode. It could provide good grayscale expression in ac PDPs.

A Line Array of Microplasma Devices With Coplanar Electrodes Operating in Argon

A line array of microplasma devices with coplanar electrodes has been fabricated, and the discharge characteristics of the microplasma devices under different argon pressures were investigated in experiments which were driven by sinusoidal voltage and alternating pulse voltage, respectively. The microcavities of the proposed device are composed of two coplanar electrodes instead of dielectric or single cathode. The voltage-current characteristics of the device driven by sinusoidal voltage show that the power loading of each microcavity could reach several kilowatts per cubic centimeter. Driven by alternating pulse voltage, the device performed a trend that the discharge current grows up first and then goes down gradually with the increase of operation pressure. Moreover, with the increase of driven frequency, the device operated with high discharge stability on both time and intensity. The proposed device possesses the advantages of simple structure and simple fabrication processes.

Equivalent circuit model and characteristic parameters for AC PDP discharge cells

In this paper, an equivalent circuit model for discharge cells of alternating current plasma display panel (AC PDP) is developed. In this model, a voltage controlled switch is introduced to describe the breakdown process of the gas discharge. And two zener diodes are introduced to describe the sustain process of the gas discharge. Three internal discharge characteristic parameters, the breakdown voltage of discharge gap, the minimum sustain voltage of discharge gap and the discharge cell capacitance ratio, are proposed. The formulas for expressing external discharge characteristic parameters by internal discharge characteristic parameters are derived. The experimental method for measuring internal characteristic parameters is developed and the measurement results for a macro discharge cell are presented.

The mechanism of plasma plume termination for pulse-excited plasmas in a quartz tube

Although the formation and propagation of plasma plume for atmospheric pressure plasmas have been intensively studied, how does the plasma plume terminate is still little known. In this letter, helium plasma plumes are generated in a long quartz tube by pulsed voltages and a constant gas flow. The voltages have a variable pulse width (PW) from 0.5 μs to 200 μs. It is found that the plasma plume terminates right after the falling edge of each voltage pulse when PW < 20 μs, whereas it terminates before the falling edge. When PW is larger than 30 μs, the duration of plasma plume starts to decrease, and the termination is found to occur at the current zero moment of the discharge current through the high-voltage electrode, which is much different from that through the ground electrode. This indicates that part of the discharge current is shunted by the plasma plume to its downstream gas region. An equivalent circuit model is developed, from which the surface charge deposited on the quartz tube is found crucia...

Microplasma mode transition and corresponding propagation characteristics controlled by manipulating electric field strength in a microchannel-cavity hybrid structure device

Plasma redistribution in a symmetric microchannel-cavity hybrid structure device has been investigated by modulating the applied electric field strength. The device array has been operated in 200 Torr of argon, driven by a 20 kHz bipolar waveform. With the existence of the intervening microchannel between microcavities, several stable modes of operation of the microplasma have been observed, including cavity mode, hybrid mode and channel mode. Transition between the modes occurs with modulation of the applied voltage from 800 to 1100 V. The characteristics of microplasma propagation in different modes are investigated and the propagation speed along diagonal direction of the device in cavity mode, hybrid and channel mode are calculated to be ~48, ~29 and ~32 km s−1, respectively. Nonhomogeneous electric field strength distribution and plasma interaction have been discussed to explain these experimental results. Emission intensity and propagation speed differences in the cavity mode between the polarities of the applied voltage are interpreted through spatially resolved measurements of the emission profile in a partial channel-cavity array.

Image-based dynamic subfield coding for improving gray scale smooth in color PDPs

Dynamic subfield coding (DSC) based on uniform sample and symmetrical segmentation for valid gray scales is proposed to resolve the lack of gray scale expression capability for static images in accumulation light emission mode. In this method, gray scale is sampled in isolated gray region, then gray scales left is segmented symmetrically and gray scales with higher histogram can be sampled in each gray region segmented. The subfield weight is the difference of adjacent sampled gray scales. So the gray scales sampled is distributed symmetrically, the gray scales sampled and subfield weight is varied according to the image. The simulation and experiment results show that the proposed method can not only express the large area background perfectly, but also keep the image details furthest and reduce the contour of static image.