Human Visual System

At the center of visual computing is human vision, which is important for two key reasons. First, many visual computing systems (such as cameras and AR/VR headsets) generate image signals that are ultimately consumed by humans. It is therefore essential to understand how the human visual system processes and interprets these signals. Second, although not the focus of this book, machine vision systems are still, in many ways, striving to match the capabilities of human vision. A deeper understanding of human vision may help inform and inspire better machine vision designs.

Our discussion will primarily focus on the early visual system, including the eye optics and the retinal processing, while touching only lightly on cortical processing — for two reasons. First, eye optics and retinal processing are relatively better understood in the scientific community compared to cortical processing. Second, many aspects of perceptual performance, such as spatial and temporal resolution, contrast sensitivity, and visual adaptation, can be largely explained by the eye’s optics and retinal function. These characteristics are frequently exploited in engineered systems such as AR glasses, where the main consideration is whether an object is visible/detectable, which the early visual system is concerned with, rather than higher-order visual functions such as object recognition, motion and depth perception, etc.

We will start from an overview of the human visual system (Chapter 2  From Light to Vision), followed by a closer look at phototransduction at the photoreceptors, the first step in seeing (Chapter 3  Photoreceptors). We will then move onto color vision (Chapter 4  Color Vision) and colorimetry (Chapter 5  Colorimetry), the quantitative study of color. We will then turn to adaptation (Chapter 6  Visual Adaptations and Constancy), understanding how our visual system adjusts its sensitivity according to the ambient environment.