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Hans Strasburger, Torsten Wüstenberg; Calibrated LCD stimulus presentation for visual psychophysics in fMRI. Journal of Vision 2006;6(6):71. doi: 10.1167/6.6.71.
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© ARVO (1962-2015); The Authors (2016-present)
Standard stimulus presentation techniques using liquid crystal (LCD) or cathode-ray tube (CRT) technology show drastic distortions in luminance and contrast characteristics across the screen and across gray levels. Common gamma-correction does not address screen inhomogeneity. Moreover, the common luminance measurement and calibration techniques are not applicable in the vicinity of an MRI scanner. With the aid of a fiber optic, we measured in our monitor screen luminances for the full space of screen position and image gray values. On that basis we developed a compensation technique that involves both luminance homogenization and position-dependent gamma correction. For fine resolution across the screen, the technique uses interpolation of gamma-curve coefficients rather than the luminance interpolation used elsewhere and thus achieves high precision with fewer parameters. Implemented in MATLAB® the calibration can be applied to both images and movies. By the technique described, images displayed to a subject in functional MRI can be specified with high precision by an image matrix of target luminance values rather than by local gray value.
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