Xu Renfeng, Wang Huachun, Thibos Larry N, Bradley Arthur
J Opt Soc Am A Opt Image Sci Vis. 2017 Apr 1;34(4):481-492. doi: 10.1364/JOSAA.34.000481.
Our purpose is to develop a computational approach that jointly assesses the impact of stimulus luminance and pupil size on visual quality. We compared traditional optical measures of image quality and those that incorporate the impact of retinal illuminance dependent neural contrast sensitivity. Visually weighted image quality was calculated for a presbyopic model eye with representative levels of chromatic and monochromatic aberrations as pupil diameter was varied from 7 to 1 mm, stimulus luminance varied from 2000 to 0.1 cd/m, and defocus varied from 0 to -2 diopters. The model included the effects of quantal fluctuations on neural contrast sensitivity. We tested the model's predictions for five cycles per degree gratings by measuring contrast sensitivity at 5 cyc/deg. Unlike the traditional Strehl ratio and the visually weighted area under the modulation transfer function, the visual Strehl ratio derived from the optical transfer function was able to capture the combined impact of optics and quantal noise on visual quality. In a well-focused eye, provided retinal illuminance is held constant as pupil size varies, visual image quality scales approximately as the square root of illuminance because of quantum fluctuations, but optimum pupil size is essentially independent of retinal illuminance and quantum fluctuations. Conversely, when stimulus luminance is held constant (and therefore illuminance varies with pupil size), optimum pupil size increases as luminance decreases, thereby compensating partially for increased quantum fluctuations. However, in the presence of -1 and -2 diopters of defocus and at high photopic levels where Weber's law operates, optical aberrations and diffraction dominate image quality and pupil optimization. Similar behavior was observed in human observers viewing sinusoidal gratings. Optimum pupil size increases as stimulus luminance drops for the well-focused eye, and the benefits of small pupils for improving defocused image quality remain throughout the photopic and mesopic ranges. However, restricting pupils to <2 mm will cause significant reductions in the best focus vision at low photopic and mesopic luminances.
我们的目的是开发一种计算方法，以联合评估刺激亮度和瞳孔大小对视觉质量的影响。我们比较了传统的图像质量光学测量方法和那些纳入了视网膜照度依赖性神经对比敏感度影响的方法。针对具有代表性的色像差和单色像差水平的老视模型眼，在瞳孔直径从7毫米变化到1毫米、刺激亮度从2000坎德拉每平方米变化到0.1坎德拉每平方米、散焦从0屈光度变化到-2屈光度的情况下，计算了视觉加权图像质量。该模型包括了量子涨落对神经对比敏感度的影响。我们通过测量5周/度时的对比敏感度，测试了该模型对每度5个周期光栅的预测。与传统的斯特列尔比和调制传递函数下的视觉加权面积不同，从光学传递函数导出的视觉斯特列尔比能够捕捉光学和量子噪声对视觉质量的综合影响。在聚焦良好的眼睛中，如果随着瞳孔大小变化视网膜照度保持恒定，由于量子涨落，视觉图像质量大致与照度的平方根成比例，但最佳瞳孔大小基本上与视网膜照度和量子涨落无关。相反，当刺激亮度保持恒定（因此照度随瞳孔大小变化）时，最佳瞳孔大小随着亮度降低而增加，从而部分补偿增加的量子涨落。然而，在存在-1和-2屈光度散焦且在明视觉水平较高、韦伯定律起作用的情况下，光学像差和衍射主导图像质量和瞳孔优化。在观察正弦光栅的人类观察者中也观察到了类似的行为。对于聚焦良好的眼睛，随着刺激亮度下降，最佳瞳孔大小增加，并且小瞳孔在改善散焦图像质量方面的益处贯穿明视觉和中间视觉范围。然而，在低明视觉和中间视觉亮度下，将瞳孔限制在<2毫米会导致最佳聚焦视力显著下降。
