Visual increment and decrement threshold curves as a function of luminance range and noise in simulated computed tomographic scans.
OBJECTIVE
The effect of luminance range compression on the visual threshold of a target in a computed tomographic (CT) scan was investigated in eight experiments.


METHODS
Both visual increment thresholds of a hot target and visual decrement thresholds of a cold target were obtained. Realistic noisy CT images simulating a scan reconstruction and partial volume blurring were tested as representative of complex medical images. Negative versions, high luminance versions, and noise-free versions of these CT images also were tested.


CONCLUSIONS
In all the noisy images, as the luminance range of the image was compressed, proportionately smaller physical luminance differences between the target and its local background were needed to reach visual threshold. However, the thresholds were the same in terms of the difference in CT numbers between target and background. Noise in terms of CT numbers sets the threshold for a wide range of display conditions. In the noise-free CTs, as the luminance range was compressed, the luminance differences between the target and background needed to reach threshold also decreased, but only marginally. However, in terms of CT numbers, the thresholds were increased.
Klymenko
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Department Computer Science, University of North Carolina at Chapel Hill.
Johnston
R E
RE
Pizer
S M
SM
D000704:Analysis of Variance; D003198:Computer Simulation; D016288:Computer Terminals; D005246:Feedback; D006801:Humans; D008027:Light; D009622:Noise; D011856:Radiographic Image Enhancement / Q000295:instrumentation / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data