Natural preference in luminosity for frame composition

We investigated whether or not frame composition spontaneously selected by individuals exhibit a natural left shift in preference of luminosity, as previously suggested, by examining biases in luminosity imprinted in photographs taken under three different conditions: (i) daytime pictures taken outside without determination of frame composition (N=4153); (ii) daytime pictures taken outside with determination of frame composition (N=4035); and (iii) pictures taken inside with determination of frame composition (N=4045). As anticipated, there was a strong vertical gradient of luminance grayscale intensity, reflecting natural day light distribution, for pictures of categories (i) and (ii). Similarly, a minor vertical gradient was detected for pictures of category (iii), indicating common room lighting conditions. To our great interest, there was a consistent leftward tilt of ca. 2 and 9° found in the vertical gradients for pictures of categories (ii) and (iii), respectively, but not for pictures of category (i). The result provides clear-cut evidence that there is indeed a natural preference for a leftward bias in luminosity for frame composition.