Grey Tone Perception in Koffka Ring Stimuli on Colored Backgrounds in Digital Media

This paper examines how different background color combinations influence the perception of grey tones in primary stimuli within modified Koffka ring configurations displayed on a computer screen. A custom software application was used with 60 observers, who adjusted perceived grey tones for three primary lightness levels (dark, medium, light) across 27 test samples combining three Koffka ring variants and chromatic backgrounds (red, blue, green). The strength of the simultaneous contrast effect was quantified using the color appearance difference ΔE00, while accompanying shifts in chroma (ΔC) and hue (ΔH) were also evaluated and analyzed by descriptive statistics, Friedman ANOVA, and post hoc Wilcoxon signed-rank tests. The results show that the effect is strongest for dark-grey tones and clearly visible on blue–green and red–green backgrounds, moderate on red–blue backgrounds, and weak or negligible for light-grey tones, with ΔC and ΔH remaining very small, indicating a predominantly lightness-based illusion. These findings provide guidance for digital media design by indicating which combinations of grey levels, spatial configurations, and background colors are most likely to produce unwanted simultaneous contrast in screen-based applications.