Hwang Alex D, Peli Eli
Schepens Eye Research Institute - Massachusetts Eye and Ear, Department of Ophthalmology, Harvard Medical School, 20 Staniford Street, Boston, MA02114, USA.
IS&T Int Symp Electron Imaging. 2016;2016. doi: 10.2352/ISSN.2470-1173.2016.16.HVEI-122. Epub 2016 Feb 14.
Contrast sensitivity (CS) quantifies an observer's ability to detect the smallest (threshold) luminance difference between a target and its surrounding. In clinical settings, printed letter contrast charts are commonly used, and the contrast of the letter stimuli is specified by the Weber contrast definition. Those paper-printed charts use negative polarity contrast (NP, dark letters on bright background) and are not available with positive polarity contrast (PP, bright letters on dark background), as needed in a number of applications. We implemented a mobile CS measuring app supporting both NP and PP contrast stimuli that mimic the paper charts for NP. A novel modified Weber definition was developed to specify the contrast of PP letters. The validity of the app is established in comparison with the paper chart. We found that our app generates more accurate and a wider range of contrast stimuli than the paper chart (especially at the critical high CS, low contrast range), and found a clear difference between NP and PP CS measures (CS>CS) despite the symmetry afforded by the modified Weber contrast definition. Our app provides a convenient way to measure CS in both lighted and dark environments.
对比敏感度（CS）量化了观察者检测目标与其周围环境之间最小（阈值）亮度差异的能力。在临床环境中，通常使用印刷字母对比图表，字母刺激的对比度由韦伯对比度定义指定。那些纸质印刷图表使用负极性对比度（NP，亮背景上的暗字母），而许多应用所需的正极性对比度（PP，暗背景上的亮字母）则没有。我们开发了一款移动CS测量应用程序，它支持NP和PP对比刺激，NP刺激模仿纸质图表。我们开发了一种新颖的改良韦伯定义来指定PP字母的对比度。通过与纸质图表比较确定了该应用程序的有效性。我们发现，我们的应用程序比纸质图表能产生更准确、范围更广的对比刺激（特别是在关键的高CS、低对比度范围内），并且尽管改良的韦伯对比度定义提供了对称性，但NP和PP CS测量之间仍存在明显差异（CS>CS）。我们的应用程序提供了一种在明亮和黑暗环境中测量CS的便捷方法。
