Project:

NCCI 2010 -National Conference on Computational Instrumentation CSIO Chandigarh, INDIA, 19-20 March 2010 ANALYSIS OF AUTO DYNAMIC INTENSITY VARIATION FOR ACTIVE DISPLAY INTENSITY CONTROL FOR WIDE BACKGROUND INTENSITY Upasna, Mandal Danvir, Karar Vinod*, Saini Surender Singh * Institute of Engineering and Technology, Bhaddal, Ropar, Punjab *Central Scientific Instruments Organisation, Chandigarh ABSTRACT: The display systems with the human eye features like automatic intensity control (AIC) under
varying background luminance conditions add more challenge to design of display systems. The AIC can be
achieved by varying the display intensity according to the background intensity level taking into account the
comfort level of the user. In this paper, various parameters important for automatic intensity control design have
been discussed and a new methodology based on look up table generated using experimental values has been
devised by which the display intensity can be adaptively varied maintaining an adequate contrast ratio in real
time mode.
1. INTRODUCTION
the major factors in the implementation of AIC The use of automatic change in display intensity with the change of background intensity enhances the comfort level of the viewer by maintaining an Background Intensity) / Background Intensity appropriate contrast ratio. The main challenge is to make the system response in real time mode and 4. AIC ALGORITHM REALIZATION
provide good contrast ratio of the scene, image or Various algorithms or methodologies like approximations by power series, exponential series, and approximation methods can be used for generation and implementation of AIC output 2. REQUIREMENT OF AIC
function but they suffer from shortcomings like large scale of error, low accuracy, complexity, non-real depends on the strength of video signal input while time operation, etc. The AIC algorithm using lookup the intensity depends on the DC level of the video table has been derived and based on experiments signal. By suitably varying the DC level of the video conducted on CRT projection display. Experimental signal, the display intensity can be adaptively varied values are based on measurements of background and a contrast ratio between 1.2 and 2.5 can be intensity and background + display intensity at maintained under varying background intensity. various settings of the user controlled intensity potentiometer. These two inputs are conditioned and 3. AIC PARAMETERS
given as input to ADC which is further processed by The photo sensor is based on eye response curve the microcontroller. A curve has been plotted and of the intensity sensor, i.e. in the wavelength region piecewise linearized. A line equation for each linear of 500-600nm. The basic block diagram of AIC tras 1.6
on
Where θ = tan-1 (∆Y/∆X) and C is user controlled Accordingly, the inputs for implementation of intensity calibrated for intensity levels from 0cd/m2 AIC algorithm are: user controlled intensity control to 6800cd/m2 converted to 0V to 2.5V corresponding and AIC sensor output voltage corresponding to the to ADC reference voltage. Three modes i.e. Day background intensity. The Contrast Ratio was one of time, night time and AIC (where major control of the intensity is done automatically through software) NCCI 2010 -National Conference on Computational Instrumentation CSIO Chandigarh, INDIA, 19-20 March 2010 mode for intensity control have incorporated. The contrast ratio can be further improved by a factor of 0.2 through user controller intensity potentiometer. The following plot shows that the contrast ratio of 1.271 to 2.20 has been achieved, as desired. The achieved curve plotted between background intensity and background intensity + display intensity is shown in figure below. 5. CONCLUSIONS
The desired contrast ratio range from 1.2 to 2.2 using look table generated through experimental values has been achieved in real time mode for the full dynamic background intensity range. 6. REFERENCES
Istvan Lamoth, “Automatic Brightness Control and Linearity Correction Circuits for Large Screen Color Oscilloscopes”, IEEE Transactions on Instrumentation and Measurement, Vol. 22, No. 2, June 1973. ii. Lamoth and G. Epprecht, "Large screen color oscilloscope for classroom use," IEEE Transactions on Education, Vol. 15, August 1972. iii. Chinn-Chann Chiang, “Brightness control system for LED lighting devices”, DIGITEK Technology Co., Ltd., Alexandria, VA US. iv. Van Antwerp, Joel C., “Automatic brightness control apparatus”, United States Patent 4514727. v. “Automatic Brightness Control Responsive to Black Level of Video Signal”, United States Patent 3597540, Motorola Inc. vi. “Optoelectronics Designer’s Catalog”,

Source: http://www.csio.res.in:8085/ncci/ICCIpdfDoc/ANALYSIS%20OF%20AUTO%20DYNAMIC%20INTENSITY%20VARIATION%20FOR%20ACTIVE%20DISPLAY%20INTENSITY%20CONTROL%20FOR%20WIDE%20BACKGROUND%20INTENSITY%20RANGE.pdf