• Title/Summary/Keyword: luminance gain

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Optical performances of flat-lamp backlights for LCD applications

  • Ko, Jae-Hyeon;Yu, Mi-Yeon
    • 한국정보디스플레이학회:학술대회논문집
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    • 2008.10a
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    • pp.1185-1188
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    • 2008
  • The on-axis luminance gain as well as the viewing-angle characteristics of flat-lamp-based backlights have been analyzed for the first time. The on-axis luminance gain on each optical film in flat-lamp backlight was smaller than that obtained from the conventional tubular-lamp-based backlight. The origin of and possible solution to this problem were suggested.

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Design of a digital filter with variable characteristics for a luminance signal processing of digirtal TV (가변 특성을 갖는 디지털 TV 휘도신호 처리용 디지털 필터 설계)

  • 왕종현;이해정;유영갑;조경록
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.21 no.1
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    • pp.67-79
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    • 1996
  • This paper presents a composite luminance signal processing system for NTSC, PAL and SECAM standards. Eaxh of the three standards employs its own specifications of subcarmier bandwidth and luminance signal waveform. The proposed system, compatible to the specifications of the three standard and B/W TV, implements variable freqneucy characteristics by controlling filter coefficients. The major features of the system are a luminance/chroma separation unit and an aperture compensation unit. The luminance/chroma separation unit employes a notch filter selection a trap freqneyc to atenuate unwanted color signals in luminance signal bands. The aperture compensation unit comprises two subunits, to provide clear color definition for each of the three standards: a primary compensation circuit and a variable compensation circuits. The proposed system yields a 40 dB gain from the chroma/luminance separation and a 10 dB gain from the aperture compensation unit.

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Study on the Luminance Properties of Optical Films for Flat-lamp Backlight Applications

  • Yu, Mi-Yeon;Park, Ji-Hee;Ko, Jae-Hyeon
    • Journal of the Optical Society of Korea
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    • v.12 no.3
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    • pp.174-177
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    • 2008
  • The luminance properties of FFL(Flat Fluorescent Lamp) backlights have been investigated in detail for the first time. The on-axis luminance gain as well as viewing-angle characteristics on various combinations of optical films were obtained from FFL backlight and compared to the results of conventional CCFL(cold-cathode fluorescent lamps) backlights. It was found that the on-axis luminance gains achieved by using optical films in the FFL backlight were lower than those in the CCFL backlight indicating that the recycling processes occurring between optical films and light sources/reflection sheet are not so effective in the FFL backlight due to the much larger area of, and thus higher absorption probability of the FFL. This result suggests that new optical films should be developed for FFL backlight and other flat-lamp backlight technologies.

Light Output Characteristics of Rounded Prism Films in the Backlight Unit for Liquid Crystal Display

  • Lee, Won-Gyu;Jeong, Jin-Ha;Lee, Ji-Young;Nahm, Kie-Bong;Ko, Jae-Hyeon
    • Journal of Information Display
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    • v.7 no.4
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    • pp.1-4
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    • 2006
  • The optical performances of rounded prism films were investigated using a ray tracing technique. The angular distribution of the luminous intensity was obtained as functions of the prism pitch and the curvature of rounded apex and valley of prism arrays. The gain of the on-axis luminance decreased with decreasing curvature (increasing diameter) and pitch. The existence of the curved area on the prism film decreased the recycling efficiency of the prism film, i.e., the rays which would otherwise have been recycled through total internal reflections via the prism surfaces were refracted on the curved regions and redirected toward directions other than the on-axis direction. Quantitative correlation between the luminance gain and the curvature in addition to the prism pitch was obtained, which might serve as basic data for the optimization of prism films and the manufacturing processes.

Experimental and Simulation Study of the Optical Performances of a Wide Grid Polarizer as a Luminance Enhancement Film for LCD Backlight Applications

  • Seo, Jae Seok;Yeom, Tae Eun;Ko, Jae-Hyeon
    • Journal of the Optical Society of Korea
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    • v.16 no.2
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    • pp.151-156
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    • 2012
  • Reflective polarizers can be used as luminance enhancement films for LCD backlights via the polarization recycling process. The optical performances of a wire grid polarizer (WGP) as a reflective polarizer adopted in edge-lit backlights were investigated by luminance evaluation and a time-domain simulation technique. The results were compared to those of a commercial dielectric multilayer film. The luminance gain factor of WGP was smaller than that of the multilayer film by 18%. This was attributed to a much larger internal loss of WGP due to light absorption by metal wires. The internal losses of both reflective polarizers and the polarization conversion efficiency of the backlight were obtained numerically based on a phenomenological model. The optical performances of WGP were optimized by using a time-domain simulation technique. The luminance gain increased and was found to become comparable to, but slightly less than the case of the dielectric multilayer film with decreasing line width.

Optical Simulation Study on the Effect of Reflecting Properties of Reflection Films on the Performances of Collimating Films for the LCD Backlight Applications

  • Lee, Jeong-Ho;Ju, Young-Hyun;Park, Ji-Hee;Lee, Ji-Young;Nahm, Kie-Bong;Ko, Jae-Hyeon;Kim, Joong-Hyun
    • Journal of Information Display
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    • v.9 no.1
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    • pp.26-32
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    • 2008
  • The dependence of optical performances of collimating films such as prism films and pyramid films on the reflecting properties of reflection films were investigated by using a ray tracing technique. The angular distribution of the luminance and the on-axis luminance gain were obtained by using a simple backlight model composed of a reflection film, a virtual flat light source, and a collimating film. Three kinds of reflecting properties were used, which were a perfect Lambertian reflector, a perfect mirror reflector, and a reflector having both diffuse and specular properties. It was found that the on-axis luminance gain was the highest in the simulation where a mirror reflector was used, while the viewing angle was the widest where the Lambertian reflector was used. This result indicates that it is necessary to optimize the simulation condition such as the reflecting properties in order to predict the optical performances of collimating films accurately. Quantitative correlation between the optical characteristics of collimating films and the reflecting properties of reflection films can be used to improve simulation technique for the development and the optimization of collimating films for LCD backlight applications.

Luminance Stabilization of Image Sequence (영상 시퀀스의 밝기변화 보정)

  • Lee, Im-Geun;Han, Soow-Han
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.14 no.7
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    • pp.1661-1666
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    • 2010
  • Due to light condition or shadow around camera, acquired image sequence is often degraded by intensity fluctuation. This artifact is called luminance flicker. As the luminance flicker corrupts the performance of motion estimation or object detection, it should be corrected before further processing. In this paper, we analyze the flicker generation model and propose the new algorithm for flicker reduction. The proposed algorithm considers gain and offset parameter separately, and stabilizes the luminance fluctuation based on these parameters. We show the performance of the proposed method by testing on the sequence with artificially added luminance flicker and real sequence with object motion.

Robust Motion Estimation for Luminance Fluctuation Sequence (조명 변화에 강건한 움직임 추정 기법)

  • Lee, Im-Geun
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.14 no.8
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    • pp.1918-1924
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    • 2010
  • This In this paper, we propose an efficient algorithm for motion estimation of the image sequences with luminance fluctuation. For such sequences, conventional motion estimation methods based on the difference of pixel values usually produce the erroneous motion information. The proposed algorithm defines the luminance fluctuation as a linear model with gain and offset parameter, and extracts motion information using gradient and phase of the corresponding local region within consecutive frames. Therefor the method is robust to the luminance change of the frames. We test our algorithm for the ground truth sequence with artificially added luminance change and motion, and real sequences corrupted by the flicker. The results shows that the proposed algorithm outperforms the conventional methods.

Flicker Reduction in Image Sequences (영상 시퀀스의 플리커 제거)

  • Lee, Im-Geun
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2010.05a
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    • pp.577-580
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    • 2010
  • This paper proposes a new algorithm for flicker reduction. Flicker is defined as unwanted luminance fluctuation in the image sequences. As the flicker degrades the performance of motion estimation or segmentation of the objects, it should be corrected before further processing. In this paper, we model the flicker effects as a linear system with gain and offset parameter and propose the new algorithm for flicker reduction. The proposed algorithm considers gain and offset parameter separately, and stabilizes the luminance fluctuation based on these parameters. We show the performance of the proposed method by testing on the sequence with artificially added luminance flicker and real sequence with object motion.

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Optical simulation of micro-pyramid arrays for the applications in the field of backlight unit of LCD

  • Lee, Ji-Young;Kim, Young-Jin;Nahm, Kie-Bong;Ko, Jae-Hyeon
    • 한국정보디스플레이학회:학술대회논문집
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    • 2006.08a
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    • pp.1343-1346
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    • 2006
  • Optical performances of micro-pyramid arrays were simulated by ray tracing technique for the application of backlight unit of LCD. The angular distribution of the luminance and the on-axis luminance gain depended on the apex angle, the refractive index, and the density of micro-pyramids. The on-axis luminance reached a maximum when the apex angle was $90^{\circ}$. It also increased as the density and the refractive index of micro-pyramids increased. The present result showed that highly-efficient optical sheet might become realized by adopting micropyramid array and corresponding development of manufacturing processes.

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