Retinal HDR images: intraocular glare and object size

Starting from measured scene luminances, the retinal images of high-dynamic-range (HDR) test targets were calculated. These test displays contain 40 gray squares with a 50% average surround. In order to approximate a natural scene, the surround area was made up of half-white and half-black squares of different sizes. In this display, the spatial-frequency distribution approximates a 1/f function of energy vs. spatial frequency. Images with 2.7 and 5.4 optical density ranges were compared. Although the target luminances are very different, after computing the retinal image according to the CIE scatter glare formula, it was found that the retinal ranges are very similar. Intraocular glare strongly restricts the range of the retinal image. Furthermore, uniform, equiluminant target patches are spatially transformed to different gradients with unequal retinal luminances. The usable dynamic range of the display correlates with the range on the retina. Observers report that appearances of white and black squares are constant and uniform, despite the fact that the retinal stimuli are variable and non-uniform. Human vision uses complex spatial processing to calculate appearance from retinal arrays. Spatial image processing increases apparent contrast with increased white area in the surround. Post-retinal spatial vision counteracts glare.