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4 May 2004 2AFC assessment of contrast threshold for a standardized target using a monochrome LCD monitor
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The DICOM Gray Scale Display Function (GSDF) relates display contrast to the contrast threshold derived from the Barton Model (CBM) of the human visual system. We have measured the contrast threshold (CT) using a monochrome medical LCD monitor and graphics card under the conditions defined by the DICOM standard and compared the results to the Barten Model. A two Alternative Forced Choice (2AFC) observer performance test was used to measure contrast threshold. The 2AFC tests were given once to a large group of observers with varied medical imaging experience. A small subset of this group was tested multiple times over several months in order to examine intraobserver variability. The mean relative contrast (CT/CBM) associated with a 75% detection rate was found to be 0.508, with a standard deviation of 0.176. For the intraobserver tests, results improved after the first 3 trials. The mean CT/CBM values (and standard deviation) for the next 9 tests were 0.0980 (0.107), 0.244 (0.0928), and 0.398 (0.0855). The results indicate that contrast substantially less than 1 CT/CBM is detected based on the statistical criteria used. This can be explained based on the criteria for detection used in the classical observer tests that form the basis for the Barten model. Additionally, our data indicates significant differences amongst observers.
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Philip Tchou, Michael J. Flynn, and Edward Peterson "2AFC assessment of contrast threshold for a standardized target using a monochrome LCD monitor", Proc. SPIE 5372, Medical Imaging 2004: Image Perception, Observer Performance, and Technology Assessment, (4 May 2004);

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