Human contrast-detail performance with declining contrast.

PURPOSE: How do display settings and ambient lighting affect contrast detection thresholds for human observers? Can recalibrating a display for high ambient lighting improve object detection?
METHODS: Contrast∕detail (CD) threshold detection performance was measured for observers using four color displays with varying overall contrast (e.g., differing maximum luminance and ambient lighting conditions). Detailed mapping of contrast detection performance (for fixed object size) was tracked as a function of: display maximum luminance, ambient lighting changes (with and without recalibrating for the higher ambience), and the performance of radiologists vs. nonradiologists.
RESULTS: The initial phase was analyzed with a hierarchical linear model of observer performance using: background gray level, maximum display luminance, and radiologist vs. nonradiologist. The only statistically significant finding was a maximum luminance of 100 cd∕m(2) display performing worse than a baseline peak of 400 cd∕m(2). The second phase examined ambient lighting effects on detection thresholds. Background gray level and maximum display luminance were examined coupled with ambient lighting for: baseline at 30, 435 uncorrected, and 435 lx with display recalibration for the ambient conditions. Results showed ambient correction improved sensitivity for small background digital driving level, but not at higher luminance backgrounds.
CONCLUSIONS: For CD study, nonradiologist observers can be used without loss of applicability. Contrast detection thresholds improved significantly between displays with peak luminance from 100 cd∕m(2) to 200 cd∕m(2), but improvement beyond that was not statistically significant for contrast detection thresholds in a reading room environment. Applying a calibration correction at high ambience (435 lx) improved detection tasks primarily in the darker background regions.