Optimal step sizes for colour and luminance staircasing

Abstract

We investigated the best step size for measuring luminous and isoluminant coloured (red or blue/tritan) detection thresholds. Stimuli were generated on a colour TV monitor as 1°, 600 msec spots at one of four eccentric (1.6°) locations. Thresholds were expressed as contrasts (%) in cardinal colour space (RG, L or BY) for incremental probes from a white background (CIE 1931 x = 0.30, y = 0.31; L=33 cd/m2). One observer (aged 28) was extensively tested, and trends were confirmed on three others (aged 25-33). Staircase step sizes varied from 0.2 to 4.8 deci-log units (dLog) with starting points chosen to he within 2-3 steps of threshold. A logarithmic staircase comprising 13 reversals was perfo..