The PASCAL Visual Object Classes Challenge

Structured-light systems are simple and effective tools to acquire 3D models. Built with off-the-shelf components, a data projector and a camera, they are easy to deploy and compare in precision with expensive laser scanners. But such a high precision is only possible if camera and projector are both accurately calibrated. Robust calibration methods are well established for cameras but, while cameras and projectors can both be described with the same mathematical model, it is not clear how to adapt these methods to projectors. In consequence, many of the proposed projector calibration techniques make use of a simplified model, neglecting lens distortion, resulting in loss of precision. In this paper, we present a novel method to estimate the image coordinates of 3D points in the projector image plane. The method relies on an uncalibrated camera and makes use of local homographies to reach sub-pixel precision. As a result, any camera model can be used to describe the projector, including the extended pinhole model with radial and tangential distortion coefficients, or even those with more complex lens distortion models.

/pdf/simple-accurate-and-robust-projector-camera-calibration-agw9yvbsw4.pdf

Simple, Accurate, and Robust Projector-Camera Calibration

The evolving explosion in high data rate services and applications will soon require the use of untapped, abundant unregulated spectrum of the visible light for communications to adequately meet the demands of the fifth-generation (5G) mobile technologies. Radio-frequency (RF) networks are proving to be too scarce to cover the escalation in data rate services. Visible light communication (VLC) has emerged as a great potential solution, either in replacement of, or a complement to, existing RF networks, to support the projected traffic demands. Despite the prolific advantages of VLC networks, VLC faces many challenges that must be resolved in the near future to achieve full standardization and to be integrated to future wireless systems. Here, we review the emerging research in the field of VLC networks and lay out the challenges, technological solutions, and future work predictions. Specifically, we first review the VLC channel capacity derivation and discuss the performance metrics and the associated variables. The optimization of VLC networks are also discussed, including resources and power allocation techniques, user-to-access point (AP) association and APs-to-clustered-users-association, APs coordination techniques, non-orthogonal multiple access (NOMA) VLC networks, simultaneous energy harvesting and information transmission using the visible light, and the security issues in VLC networks. Finally, we propose several open research problems to optimize the various VLC networks by maximizing either the sum rate, fairness, energy efficiency, secrecy rate, or harvested energy.

/pdf/on-optimizing-vlc-networks-for-downlink-multi-user-imw4ngcf2j.pdf

On Optimizing VLC Networks for Downlink Multi-User Transmission: A Survey

This letter proposes an asymmetrical hybrid optical orthogonal frequency division multiplexing (AHO-OFDM) scheme for dimmable visible light communication systems. In the proposed scheme, either asymmetrically clipped optical OFDM (ACO-OFDM) or pulse-amplitude-modulated discrete multitone (PAM-DMT) signal is inverted and then both the signals are combined for transmission, where pulsewidth modulation is no longer required for dimming control. The power of ACO-OFDM and PAM-DMT signals is adjusted so that the amplitude of the combined AHO-OFDM signal is asymmetrical, which could utilize all the available subcarriers as well as the entire dynamic range of light-emitting diodes with various dimming levels. Simulation results show that the proposed scheme could achieve a wide dimming range with a small throughput fluctuation.

/pdf/asymmetrical-hybrid-optical-ofdm-for-visible-light-33u0hcupr8.pdf

Asymmetrical hybrid optical OFDM for visible light communications with dimming control

Calibration of fringe projection profilometry: A comparative review

This letter considers the efficient utilization of energy in a visible light communication (VLC) system. A joint brightness control and data transmission are presented to reduce the total power consumption while satisfying lighting and communication requirements. An optimization problem is formulated to determine the optimal parameters for the input waveform of light emitting diode (LED) lamps; this problem reduces the total energy consumption of the LED lamps while ensuring the desired brightness and communication link quality. The simulation results show that the proposed scheme increases the energy efficiency of the VLC system.

Energy-Efficient Brightness Control and Data Transmission for Visible Light Communication

In this work we propose a novel method to calibrate the projector. Calibration of the projector deals with the calculation of geometric parameters of the projector which are intrinsic and extrinsic parameters. An un-calibrated camera assists the process of finding the geometric parameters for projector. This method exploits the fact that a projector can be treated as inverse camera. The camera captures the scene and saves it as an image while the projector projects an image on the scene. Camera to projector transformation is used to make the projector able to see the calibration pattern. Then the projector is calibrated in a similar fashion like camera. Real data is used to evaluate the proposed method of projector calibration and good results are obtained.

Projector Calibration for 3D Scanning Using Virtual Target Images

http://www.scielo.org.mx/pdf/jart/v12n1/v12n1a8.pdf

Projector Calibration for Pattern Projection Systems

Multiclass semantic image segmentation is widely used in a variety of computer vision tasks, such as object segmentation and complex scene understanding. As it decomposes an image into semantically relevant regions, it can be applied in segmentation of face images. In this paper, an algorithm based on multiclass semantic segmentation of faces is proposed using conditional random fields. In the proposed model, each node corresponds to a superpixel, while the neighboring superpixels are connected to nodes through edges. Unlike previous approaches, which rely on three or four classes, the label set is extended here to six classes, i.e. hair, eyes, nose, mouth, skin, and background. The proposed framework is evaluated on standard face databases FASSEG, FIGARO, and LFW. Experimental results reveal that the performance of the proposed model is comparable with state-of-the-art techniques on these standard databases.

/pdf/multiclass-semantic-segmentation-of-faces-using-crfs-18b7hb56n0.pdf

Multiclass semantic segmentation of faces using CRFs

This paper presents a joint blind and light control scheme for lighting energy optimization in a lighting control system. The proposed scheme utilizes the maximum available daylight without any gla...

Irfanud Din

Papers

Energy-Efficient Brightness Control and Data Transmission for Visible Light Communication

Projector Calibration for 3D Scanning Using Virtual Target Images

Projector Calibration for Pattern Projection Systems

Multiclass semantic segmentation of faces using CRFs

Joint blind and light control for lighting energy reduction while satisfying light level and anti-glare requirements