Yangyu Fan

Joint LED dimming and high capacity visible light communication by overlapping PPM

Piggybacking communication by illumination LEDs provides additional valuable functionality to LED lighting fixtures as optical communication transmitters at little cost. However, joint dimming control and high data-rate communication requires proper supporting protocols under the bandwidth limitation of LEDs. This paper applies overlapping pulse position modulation (OPPM) to achieve high capacity communication and flexible dimming. It then analyzes both illumination and communication performance in terms of dimming range, flicker severity index, cutoff data rate, and power and bandwidth efficiencies, all comparing against OOK and variable PPM modulation schemes. The results show the best performance using OPPM, making it an ideal candidate technology for emerging visible light communication.

The color shift key modulation with non-uniform signaling for visible light communication

Color shift key (CSK) modulation method is a new modulation method for visible light communication (VLC) system, which transmits information through the lights color property of a multi-color light source, typically a RGB LED. This paper analyzes the illumination and communication performances of CSK signals, including flicker effect, dimming range, color rendering index (CRI), luminous efficacy rate (LER), variable data rate and error probability, and also generates the optimized power weights combination group of the red, green and blue light emitted from a RGB LED, which meet the current illumination requirements, through a 2 level non-uniform signaling method, and analytical and simulation result shows a not good enough bit error rate (BER) performance. Maximum correlation coefficient and minimum RGB space distance demodulation methods with better BER performance are also discussed, simulation result shows a close relationship between the BER performance and both the entire valid CSK signals and demodulation method. Finally, a tradeoff of the CRI is discussed.

Vector morphological operators in HSV color space

In HSV color space, the current vector morphological operators have low capability to reduce color noise caused by hue and saturation in color image processing. Because they sort the color pixels according to the hierarchical ordering of V, S, H, which is against the equal principle of the three channels in color image processing. A novel vector ordering based on the combination of H, S and V is proposed in this paper, and the associated vector morphological erosion, dilation and composite filtering operators are defined. Compared with the popular vector morphological operators, experimental results show that the new operators can reduce the color noise effectively without any new color pixels while preserving the image details. And the filtered images have higher peak signal-to-noise ratio (PSNR) and lower mean absolute error (MSE).

Comparison of pulse position modulation and pulse width modulation for application in optical communications

Different modulation methods for optical wireless have different power and bandwidth efficiencies. Each approach has a direct bearing on the quality and effectiveness of wireless optical communications. As two prime examples, pulse position modulation (PPM) and pulse width modulation (PWM) are compared. The comparison includes the power and bandwidth efficiencies, the power spectrum distribution, and the ability to resist intersymbol interference. Compact system models of multilevel digital PPM (L-PPM), and multilevel digital PWM (L-PWM) are also introduced. The results show that L-PPM has advantages in power efficiency and an approximately uniform spectral distribution, whereas L-PWM has a greater ability to resist intersymbol interference.

Colour edge detection based on the fusion of hue component and principal component analysis

Hue component is generally denoted by angle value, so the conventional edge detection operators are incapable to accurately detect edges of hue component. As a result, the popular methods of colour image edge detection usually omit the role of hue component, thus missing some edges caused by hue changes. The authors propose a novel colour edge detection method based on the fusion of hue component and principal component analysis to solve the above problems. First, a novel computational method of hue difference is defined, and then it is applied to classical gradient operators to obtain accurate edges for hue component. Moreover, complete object edges can be obtained by using the edge fusion of the first principal component and hue component of colour image with low-computational complexity. Experimental results show that the proposed approach not only can act on hue component directly and obtain accurate edges caused by hue changes, but also is effective and easy to implement.

Adjustable weighting image contrast enhancement algorithm and its implementation

Image enhancement is one of the most important techniques in digital imaging processing fields. Traditional global histogram equalization usually causes excessive contrast enhancement while local histogram equalization may cause block effect. To overcome these problems, a new method for image contrast enhancement is developed. The novelty is that the weighted average of histogram equalization and exponential transformation are combined and the level of the contrast improvement is adjustable by changing the weighting coefficients. The proposed algorithm not only achieved adjustable contrast enhancement, for color image, it also weakened the situation of lacking color due to the risen of intensity, thus increasing the image saturation. Experimental results show that the proposed algorithm has good performance on enhancing contrast and color for a majority of images mostly taken by the authors.

Visible Light Positioning Based on LED Traffic Light and Photodiode

This paper presents visible light positioning (VLP) techniques based on a traffic light and photodiodes. The position of a vehicle can be determined using both the traffic light position information obtained through a visible light communication (VLC) link and the time difference of arrival (TDOA) of the traffic light signal to two photodiodes mounted in the front of the vehicle. Methods for VLP with one traffic light and two traffic lights are both proposed, and the error due to the non-coplanar effect is studied and the related coplanar rotation methods for both cases are developed. The numerical result shows bias performance of the positioning methods with coplanar rotation is much better than the ones without coplanar rotation, and the effects of the vehicle distance to traffic light and vehicle speed are also discussed.

A new method for calibrating depth and color camera pair based on Kinect

In this paper, we present a method that can calibrates color camera and depth camera of Kinect simultaneously, and finally get the relative pose between them. The calibration process for color camera and depth camera is designed by taking advantage of two different method respectively. As we know, the depth information can be acquired readily from the depth image, however, under the consideration of the fuzzy boundary and the overlapping of object in depth image, we choose using one-dimensional object for calibrating depth camera and propose a nonlinear method to optimize its intrinsic parameter. As for color camera calibration, we design a cross shape object for calibration and validation. Both methods are strongly robust to noise and much easier to implement. The experiment result shows a better accuracy in comparison with the proprietary calibration procedure of the manufacturer.

Reshaping 3D facial scans for facial appearance modeling and 3D facial expression analysis

3D face scans have been widely used for face modeling and face analysis. Due to the fact that face scans provide variable point clouds across frames, they may not capture complete facial data or miss point-to-point correspondences across various facial scans, thus causing difficulties to use such data for analysis. This paper presents an efficient approach to represent facial shapes from face scans through the reconstruction of face models based on regional information and a generic model. A hybrid approach using two vertex mapping algorithms, displacement mapping and point-to-surface mapping, and a regional blending algorithm are proposed to reconstruct the facial surface detail. The resulting models can represent individual facial shapes consistently and adaptively, establishing the facial point correspondence across individual models. The accuracy of the generated models is evaluated quantitatively. The applicability of the models is validated through the application for 3D facial expression recognition based on the databases of static 3DFE and dynamic 4DFE. A comparison with the state of the art has also been reported.

Human gesture recognition using orientation segmentation feature on random rorest

In the field of gesture recognition, one of the major challenges lies in that different user may sign different style of gesture. Traditional exemplar-based methods are vulnerable to gesture scaling and hand location translating. To overcome such disadvantage, we propose an efficient and inexpensive solution for classifying hand gestures by defining an invariant feature and applying it on random forest. One of the prominent characteristics of gesture is the underlying sequence structure, which can be greatly distinguished from other gestures. Hence, direction of gesture sequence segments has been established as simple comparison features for training random forest classifier, and then predicting gestures at sign piece level. The property of this feature determines that our recognition method can invariant to gesture scaling and hand location translating. It is free to act gesture at any angular field of view and not subject to different acting style of signer. The results show that the performance of proposed method outweighs other state-of-art methods for gesture recognition.