Retinal HDR Images: Intraocular Glare and Object Size

Starting from measured scene luminances, we calculated the retinal images of High Dynamic Range (HDR) test targets. 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. We compared images with 2.7 and 5.4 optical density ranges. Although the target luminances are very different, after computing the retinal image according to the CIE scatter glare formula, we have 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. 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. Our spatial image processing increases apparent contrast with increased white area in the surround. Human neural spatial vision tends to counteracts optical glare.