Contrast Sensitivity Functions for HDR Displays-猫眼课题宝

DOI：

10.2352/issn.2694-118x.2020.lim-28

发表时间：

2020-09

期刊：

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其他

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作者：

Minjung Kim;M. Ashraf;M. Pérez-Ortiz;J. Martinovic;S. Wuerger;Rafał K. Mantiuk

对比敏感度函数（CSF）表征了人类视觉系统在不同空间频率下的敏感度。然而，很少有人知道在亮度超过1000 cd/m2的CSF，特别是颜色。在这里，我们测量的对比灵敏度在背景亮度从0.02 cd/m2到7000 cd/m2和三个颜色方向（黑白或无色，红绿色，黄紫色）。刺激是在高动态范围显示器上显示的各种空间频率（0.125至6cpd）的Gabor贴片（峰值亮度：15，000 cd/m2）。我们发现，消色差的对比敏感度有一个倒U形作为背景亮度的函数，在200 cd/m2的峰值灵敏度，而红，绿和黄，紫对比敏感度是单调的背景亮度的函数，饱和在200 cd/m2。基于这些测量，我们开发了一个模型，预测对比敏感度的平均观察者。该模型适用于高动态范围成像。空间视觉是指能够看到图像强度在空间上的变化;它是我们理解人类视觉的基本要素之一。现有的工作主要集中在刺激可见性作为空间频率的函数[4，18，7，14，16，13，3]。典型的实验测量检测目标刺激所需的最小对比度（对比度阈值），其指示视觉系统对该空间频率的敏感度（对比敏感度）;作为空间频率的函数的对比敏感度的值被称为对比敏感度函数（CSF）。见[20]的模型和全面审查的消色差对比度检测。然而，很少有人知道在非常高和非常低的亮度水平的对比灵敏度。对于消色差对比度，存在亮度高达约1000 cd/m2的测量结果[19，12];在这种极端水平下不存在颜色对比度的测量结果。在这里，我们描述的对比灵敏度在很宽的频率范围内，颜色，和亮度。我们还提出了一个平均（标准）观察者的对比敏感度的计算模型。因此，我们的数据和模型一起告知视觉系统如何在高动态范围（HDR）显示器可以达到的非常高和低的亮度水平下运行。关于我们工作的更详细描述，包括额外的实验，请参见[23]。对比度检测实验我们测量了目标刺激的对比度阈值，在三个颜色方向和亮度范围从0.02 cd/m2（低中间视觉）到7000 cd/m2（高明视）。刺激刺激是通过将高斯包络乘以以高斯峰值为中心的正弦光栅而创建的Gabor贴片（图1）。光栅的空间频率f = 0.5、1、2、4或6个周期/视角（cpd），高斯包络的宽度为σ = 0.5 f−1视觉度;因此，所有刺激都显示出相同的周期数（“固定周期”），但大小随f的变化而变化。这样的刺激使我们能够将可见的周期数以及刺激大小作为建模的附加参数。围绕与D 65同色异谱的中性灰色（白色）（CIE 1931 x，y = 0.3127，0.3290）调制Gabor。颜色调制在DerringtonKrauskopf-Lennie（DKL）空间中定义[6]，其基本方向对应于视锥反应的组合：无色（L+ M），红-绿（L-M）和黄-紫（S-（L+M））。DKL空间允许与设备无关的彩色刺激调制的定义，因此，与文献中的CSF测量进行比较。

Contrast sensitivity functions (CSFs) characterize the sensitivity of the human visual system at different spatial frequencies. However, little is known about CSFs at luminances above 1000 cd/m2, especially for color. Here, we measured contrast sensitivities at background luminances from 0.02 cd/m2 to 7000 cd/m2 and for three color directions (black-white or achromatic, red-green, and yellow-violet). Stimuli were Gabor patches of various spatial frequencies (0.125 to 6 cpd), displayed on a high dynamic range display (peak luminance: 15,000 cd/m2). We found that achromatic contrast sensitivity has an inverted Ushape as a function of background luminance, with peak sensitivity at 200 cd/m2, while red-green and yellow-violet contrast sensitivities were monotonic functions of background luminance, saturating at 200 cd/m2. Based on these measurements, we developed a model that predicts contrast sensitivity for the average observer. This model is intended for applications in high dynamic range imaging. Introduction Spatial vision refers to the ability to see variations of image intensity across space; it is one of the basic elements in our understanding of human vision. Existing work has largely focused on stimulus visibility as a function of spatial frequency [4, 18, 7, 14, 16, 13, 3]. A typical experiment measures the minimum contrast required to detect a target stimulus (contrast threshold), which indicates the sensitivity of the visual system to that spatial frequency (contrast sensitivity); the value of contrast sensitivity as a function of spatial frequency is known as the contrast sensitivity function (CSF). See [20] for a model and comprehensive review of achromatic contrast detection. However, little is known about contrast sensitivity at very high and very low luminance levels. For achromatic contrast, measurements exist for luminance up to approximately 1000 cd/m2 [19, 12]; no measurements exist for color contrast at such extreme levels. Here, we describe contrast sensitivity over a wide range of frequencies, colors, and luminances. We also present a computational model of contrast sensitivity for an average (standard) observer. As such, our data and model together inform how the visual system operates at the very high and low luminance levels that high-dynamic-range (HDR) displays can reach. See [23] for a more detailed description of our work, including additional experiments. Contrast Detection Experiment We measured contrast thresholds for target stimuli with in three color directions and at luminances ranging from 0.02 cd/m2 (low mesopic) to 7000 cd/m2 (high photopic). Stimuli The stimuli were Gabor patches created by multiplying a Gaussian envelope with a sinusoidal grating centered at the peak of the Gaussian (Fig. 1). The gratings were of spatial frequencies f = 0.5, 1, 2, 4, or 6 cycles per degree of visual angle (cpd), and the width of the Gaussian envelope was σ = 0.5 f−1 visual degrees; thus, all stimuli showed the same number of cycles (‘fixed-cycles’), but varied in size as a function of f . Such stimuli allowed us to treat the visible number of cycles, and therefore stimulus size, as an additional parameter for modeling. The Gabors were modulated around a neutral grey (white) that was metameric with D65 (CIE 1931 x, y = 0.3127, 0.3290). Color modulations were defined in DerringtonKrauskopf-Lennie (DKL) space [6], whose cardinal directions correspond to combinations of cone responses: achromatic (L+ M), red-green (L−M), and yellow-violet (S− (L+M)). DKL space allows a device-independent definition of the chromatic stimulus modulations, and thus, comparisons with CSF measurements in literature.

Contrast Sensitivity Functions for HDR Displays

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