contrast threshold


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contrast threshold

[′kän‚trast ‚thresh‚hōld]

contrast threshold

1. The minimum perceptible contrast for a given state of adaptation of the eye.
2. The luminance contrast which can barely be detected by an observer.
References in periodicals archive ?
The contrast threshold was measured using the psychophysical method of two-alternative forced choice in which the spatial frequency (vertical sinusoidal grating) was varied; the method was adapted from Wetherill and Levitt (26).
suggested that, of the 2 chromatic contrast thresholds measured after MH surgery, the red-green contrast threshold (RGCT) showed a significantly stronger correlation with postoperative BCVA improvement than did the Tritan contrast threshold (TCT).
The test was repeated twice, and the last correct response for each row was accepted as the contrast threshold for the corresponding spatial frequency.
In addition, the contrast of the stimuli in the amblyopic eye was fixed at 100%, which was far above the contrast threshold. Previous reports have found that the amblyopic eye's perception is intact at suprathreshold contrast level [19, 20].
In general, the just-noticeable difference (JND) contrast threshold [DELTA][B.sub.t] is given by
The Bits++ Processor was used to expand the range of brightness of the screen from 256 (or [2.sup.8]) to 16.384 ([2.sup.14]) grayscale levels, allowing us to test the contrast threshold accurately.
But a 30-m aperture will offer unprecedented angular resolution, so observers should be able to probe directly the tiny habitable zones of a small sample of M dwarf stars whose potentially habitable planets are brighter than the [10.sup.-8] contrast threshold. This capability complements that of space-based missions, which can achieve better contrast (because there's no atmosphere in space) but will likely not be large enough to achieve the extremely small angular resolution of their ground-based counterparts.
The mean contrast threshold in the test group at 2cpd, 5cpd, and 25cpd SFs was 30.4, 26.3, and 39.0, respectively; better results at 5cpd is indicative of band pass (better contrast sensitivity for middle SFs).
The second includes the new ability of systems to be characterized by a system contrast threshold function just like the human eye, and a new target task performance metric that can provide more accurate performance predictions than the previous limiting frequency methods.
The reciprocal of the contrast threshold that is required for detection is contrast sensitivity.
We used the same suprathreshold method, phases and background angular frequencies with reduced constant contrast set to five times the respective test angular frequency contrast threshold. We expect to observe maximum summation effects at test angular frequencies due to this reduction in background contrast.