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G. Dagnelie, K. M. Kramer, G. J. Seifert, L. Yang, G. D. Havey; The Eye Pod: A Calibration and Monitoring Tool for Screen-Based Vision Research. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3565.
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Computer-driven vision tests on CRT and LCD screens are ubiquitous, thanks to widely available and affordable hardware. However, existing calibration tools for screen resolution, pixel size, gamut, chromaticity, gamma, and frame rate tend to be expensive, cumbersome, and/or inaccurate. Moreover, none are designed to monitor experimental conditions such as ambient illumination or subject position. We developed a prototype for such a system in a phase I STTR.
The prototype consists of a circular pod, containing three TAOS TSL238 sensors in a 50 mm equilateral triangle to measure horizontal and vertical pixel positions, and hence sizes, and a TAOS TSC230 sensor array collecting red, green, blue, and clear screen emissions through an IR-blocking filter to measure frame rate, gamma, and gamut; and a second probe containing a MaxSonar EZ1 range finder, to measure subject-to-screen distance, and two TAOS TSL2561 sensors with 45° acceptance and diffusing windows, to measure directly incident and global ambient illumination, respectively. A Microchip 18F8722 PIC processor, FTDI FT245R USB-to-parallel FIFO interface and a Xilinx Spartan-II XC2S30 FPGA assure sensor control and communication with a host PC.
Our initial prototype allows pixel size, frame rate and gamma to be measured with better than 1% accuracy. Using separate LCD and CRT screen tables, (x,y,Y) coordinates of the screen primaries can be determined within 2%. The range finder measures subject-to-screen distance within 1" (25 mm). Assistants quickly learn to operate the system, perform calibrations and set up the monitoring unit. We are starting training with normally and partially sighted subjects to perform these tasks independently. We are designing a phase II prototype that will improve chromaticity (1%), range-finding (≤0.25") and ambient illumination measures, and provide Mac and Linux compatibility. Our current prototype will be demonstrated at the meeting.
This calibration and monitoring tool should be helpful in vision research labs in conjunction with many vision tests. We also expect it to enable calibrated computer-based vision testing in general health clinics, schools, and similar settings where specialized visual function test equipment may not be available.
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