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James Schirillo, Matthew Riddle, Rumi Tokunaga; Size makes a difference: Estimating lightness and luminance contrast with real light. Journal of Vision 2011;11(11):368. doi: 10.1167/11.11.368.
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It should be possible to match a crisp luminance edge produced by a spotlight to a reflectance edge. In experiment one 40 observers matched either the luminance contrast or lightness produced by a luminance edge from either a large spotlight or a large gray paper to one of 20 small reflectance edges. In experiment two different observers made the same matches only the spotlight and gray paper edges were equal in size to each of the 20 reflectance edges. In experiment one the spot luminance contrast was 9.5:1 and 3.2:1 for increments and decrements, respectively while for the gray paper it was 8.7:1 and 2.9:1 for increments and decrements, respectively. In experiment one, we found large inter-individual variations with the luminance and lightness matches. Second, observers made the histograms of lightness and luminance matches very close to each other, suggesting that when asked to make a luminance match they actually performed a lightness match. Lastly, the luminance contrast and lightness underestimated the actual luminance contrast produced by the spotlight by 24% for decrements and 35% for increments and for the paper by 37% for decrements and 36% for increments. In experiment two the inter-individual variations were reduced overall, while the histograms of lightness and luminance matches remained very close to each other. The spotlight luminance contrast was 4.6:1 and 3.6:1 for increments and decrements, respectively while for the gray paper it was 8.5:1 and 2.8:1 for increments and decrements, respectively. Importantly, luminance contrast and lightness underestimated the actual luminance contrast produced by the spotlight by 0% for decrements (perfect lightness constancy) and 3% for increments and for the paper by 22% for decrements and 22% for increments. Thus, the size of the target affects lightness and luminance contrast matches which are in agreement with Gilchrist et al.'s (1999) area rule.
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