Dark/bright asymmetries arise from global statistical image properties.
(A,B) White noise images (indicated throughout with yellow outlines) and naturalistic noise images (indicated throughout with green outlines) were separated into dark and bright features as described for the natural images analysis. (C-F) In white noise images, the distributions of visual features are identical for brights and darks. (Note that the spatial frequency distribution for these images is not flat due to the bandpass nature of the contrast filters.) (G-J) Naturalistic noise images were generated to reflect several global features of natural images, but were otherwise unstructured. In naturalistic noise images, many of the dark/bright asymmetries in natural images are reproduced. (K-N) Dark-to-bright ratios are shown for each type of noise as in Fig 3 to further illustrate the areas of agreement and disagreement. Yellow lines indicate white noise, green lines indicate naturalistic noise, and grey lines show the results for natural images from Fig 3 for comparison.