Visible Light Communication using an HFR camera-projector system

Atul Sharma1†, Kohei Shimasaki2, Takeshi Takaki1 and Idaku Ishii1

1Department of System Cybernetics, Hiroshima University, Hiroshima, Japan2Digital Manufacturing Education Research Center, Hiroshima University, Hiroshima, Japan

(Tel: +81-82-424-7692; E-mail: atul@robotics.hiroshima-u.ac.jp1)

Abstract: We propose a novel method for streaming the real-time video transmission using projector-camera based Visuallight communication (VLC) system. Our method uses a high frame rate (HFR) projector which can project an encodedcolor input video sequence into binary image patterns modulated at thousands of frames per second (fps), and an HFRvision system which can capture and decode these binary patterns into the input color video sequence with real-timevideo processing. In this system, we introduce a protocol for the projector-camera based VLC system, in which theHFR-projector is fed with the multi-level colored video sequence which is encoded using gray-code before transmissionto avoid ambiguity caused by interference at the pixel boundaries.

Keywords: High speed vision, real-time video processing, visual light communication, video streaming

1. INTRODUCTIONWith the recent development of CMOS image sen-

sors, high-speed CMOS imagers offer image processingat high frame rates which is highly effective in recogniz-ing a wide variety of high speed phenomena in the realworld. Various high-frame-rate (HFR) vision systemshave been developed [1, 2] which can process images athundreds or thousands of frames per second. HFR projec-tor systems based on digital micro-mirror device (DMD)technology [3] are used with HFR camera systems in ap-plications such as structured-light-based 3-D sensing andprojection mapping.

In this paper, we introduce a high-speed camera-projector system for real-time 24-bit RGB color videostreaming at dozens of frames per second with visiblelight communication (VLC) as illustrated in Figure 1.

Fig. 1 Block Diagram of HFR VLC

2. METHODOLOGY2.1. Encoding

The transmission process is shown in Figure 2 inwhich the projector is fed with gray-code encoded videosequence which is further binary-modulated using pro-jector. Gray-coded images reduces the ambiguity and bittoggle along the gradient resulting in proper image re-construction. Also, the rendering of encoded gray-codevideo sequence along with pixel-wise binary image pat-terns projection is difficult for human eye to decode it andthus helps in a secured transmission of video sequence.

† Atul Sharma is the presenter of this paper.

The header information is embedded to the gray-code en-coded video sequence which contains data of frame num-bers, bit plane sequence of each channel and synchro-nization block for reconstructing video sequence at thereceiver.

2.2. DecodingAs shown in Figure 1 the receiver system consists of

HFR monochrome vision sensor and decoding system.Figure 3 explains the decoding process of captured im-ages from monochrome HFR camera. The transmitterand receiver system are not synchronized using any hard-ware triggered circuit. Thus, projected binary images iscaptured at a frame rate thrice the projected frame rateout of which a better image is selected for reconstruc-tion. Various background textures can be used as back-ground scene is subtracted from projected content whichprovides more robustness to the system and improves theoutput video quality.

3. EXPERIMENT

The video sequence selected for experiment is down-loaded from the website www.bigbuckbunny.org(c) copy-right 2008, Blender Foundation. As shown in the ex-perimental setup Figure 4, the Texas Instruments DLPLightcrafter 4500 projector is used for projecting thebinary-modulated images at 1041 fps and Photron SA-X2monochrome camera is used to acquire the 12-bit grey-level images having a resolution of 512×512 at a framerate of 3125 fps. The input video to projector is stream-ing at a frame rate of 30 fps which further slows down to16∼21 fps due to conversion of pure binary-code basedimage into gray-code and addition of header information.As explained in decoding section, the frame number andbit-plane sequence information from the header is used toreconstruct a 24-bit RGB color image. From Figure 5 wecan compare the different frames of reconstructed videohaving resolution 505×455 at receiver with the originalimages having resolution 1920×1080 and they are foundto be similar in visual appearance.

2019 58th Annual Conference of theSociety of Instrument and Control Engineers of Japan (SICE)September 10-13, 2019, at Hiroshima, Japan

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Fig. 2 Transmitter in HFR VLC

Fig. 3 Receiver in HFR VLC

Fig. 4 Experiment Setup

4. CONCLUSIONIn this paper, the proposed HFR projector-camera

system works as VLC-system for tansmitting real-timevideo. In future, the problem of synchronization ofcamera-projector can be solved by introducing visualfeedback system at receiver.

REFERENCES[1] I. Ishii, et.all,”2000 fps Real-time Vision System with

High-frame-rate Video Recording,” Proc. IEEE Int.Conf. on Robo. and Automat.,1536–1541, 2010.

[2] Atul Sharma, et.all, ”Super High-Speed Vision Plat-form That Can Process 1024x1024 Images in RealTime at 12500 Fps,” Proc. IEEE/SICE Int. Symp. onSyst. Integr.,544-549, 2016.

[3] L.J. Hornbeck, ”Digital Light Processing andMEMS: Timely Convergence for a Bright Future”,Plenary Session, SPIE Micromachining and Micro-fabrication’95, 1995.

Fig. 5 Comparison of Images from Original video withthat of reconstructed video

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