A Chromaticity‐Based Warm‐Cool Model Integrated With the Neutral White Locus

ABSTRACT This study aimed to develop a chromaticity‐based warm‐cool model to predict perceived warmth in both chromatic and near‐white colors. Two psychophysical experiments were conducted using the paired comparison method in a dark room, with equal‐luminance stimuli presented on a calibrated LCD. Experiment 1 examined 15 chromatic stimuli spanning a broad range of chromaticities, while Experiment 2 involved 25 near‐white stimuli across various CCT and Duv values. Thirty observers, including 15 males and 15 females, participated in each experiment, performing paired comparisons by selecting the stimulus that appeared “warmer” in each trial. Based on the experimental results, a new warm‐cool model was developed as a linear function of the CIE 1976 u' and v' chromaticity coordinates, allowing warm‐cool predictions without the need for perceptual attributes such as hue angle. In this model, the warmth perception is defined by the signed distance to a “reference line” in the u'v' chromaticity diagram, which passes through CIE Illuminant D75, previously identified as the most neutral white. Building on this, the study introduces a warm‐cool scale (), which offers significantly improved perceptual uniformity over CCT. The integration of the scale with the previously established neutral white locus offers a perceptual alternative to the Planckian locus and CCT.