Peli E
Physiological Optics Unit, Tufts University School of Medicine, Boston, Massachusetts.
Optom Vis Sci. 1992 Jan;69(1):15-24. doi: 10.1097/00006324-199201000-00003.
Image enhancement as an aid for the visually impaired may improve visibility of TV programs and provide portable visual aid. This paper describes the current techniques for image enhancement and their underlying models. The limitations of the various techniques and of potential methods of implementation are high-lighted. Initial work in this area was based on a linear model. The finite dynamic range available in the video display and contamination of the enhanced image by high spatial frequency noise limited the model's usefulness. I propose a method to address some limitations of the original model that considers the nonlinear response of the visual system and requires enhancement of subthreshold spatial information only. This modification may increase the dynamic range available by decreasing the range previously used by the linear models to enhance visible details. However, for the modified technique to be most effective, the enhancement has to be continuously tuned, based on the patient's visual loss and the spatial frequency content of the displayed images. The implications of these limitations for the potential implementation in TV are discussed. Implementation of an image-enhancing visual aid in a head-mounted, binocular, full-field, virtual vision device may cause substantial difficulties. Patient adaptation may be difficult due to head movement and interaction of the vestibular system response with the head-mounted display. An alternate, bioptic design is proposed in which the display is positioned above or below the line of sight to be examined intermittently, possibly in a freeze-frame mode. Such implementation is also likely to be less expensive, enabling more users access to the device.
图像增强作为一种视障辅助手段，可提高电视节目的可视性并提供便携式视觉辅助工具。本文介绍了当前的图像增强技术及其基础模型。强调了各种技术以及潜在实现方法的局限性。该领域的早期工作基于线性模型。视频显示器可用的有限动态范围以及增强图像中高空间频率噪声的干扰限制了该模型的实用性。我提出了一种方法来解决原始模型的一些局限性，该方法考虑了视觉系统的非线性响应，并且仅需要增强阈下空间信息。这种修改可能会通过减少线性模型先前用于增强可见细节的范围来增加可用的动态范围。然而，为了使修改后的技术最有效，必须根据患者的视力丧失情况和所显示图像的空间频率内容对增强进行持续调整。讨论了这些局限性对电视潜在应用的影响。在头戴式、双目、全视野、虚拟视觉设备中实现图像增强视觉辅助工具可能会带来重大困难。由于头部运动以及前庭系统反应与头戴式显示器的相互作用，患者适应可能会很困难。提出了一种替代的双眼视觉设计，其中显示器位于视线之上或之下，以便间歇性地检查，可能采用定格模式。这种实现方式可能成本也更低，使更多用户能够使用该设备。
