Part IV: Human Vision
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The material about human vision in this volume is currently under development.
For now, please refer to the chapters in Foundations of Vision.
The new material in this volume will emphasize the human vision engineering standards, reducing the emphasis on biology that is part of FOV.
Human Vision Topics
Vision scientists have learned a great deal about the first stages of vision. We have excellent measurements of how the eye’s optics (the cornea and lens) transform light from the world into an image on the retina, and we know how the retina’s photoreceptors encode that image into neural signals. This knowledge serves as a practical guide for designing any system that reproduces images for people.
Consider color. A camera designed for human viewing should capture the same portion of the electromagnetic spectrum that we see: visible light. Capturing less of the spectrum would lead to poor color reproduction. Capturing more—like infrared or ultraviolet—would be wasteful, consuming resources to record information we can’t see anyway. Worse yet, if we added these signals into a reproduction, the appearance would fail to match what we see. Our knowledge of human wavelength sensitivity sets a clear target for an image system designed for consumer photography.
Spatial resolution presents a different challenge. It would be a disappointment if a camera failed to capture details as fine as those the human eye can resolve. We expect our photos to be at least as sharp as what we see. However, unlike color, people are generally pleased if a camera captures a scene at a finer resolution than the eye encodes. We zoom in on the digital image to see details we might have missed. This extra information doesn’t interfere with the viewing experience; it just requires more storage and processing power.
So, we have two different engineering constraints derived from human vision:
- Wavelength: Human vision sets a target range.
- Spatial Resolution: Human vision sets a minimum bar.
In this section of the book, we will review the way our visual system encodes wavelength and spatially samples the image. Understanding the human visual system properties is good guidance for what we cannot see. This is essential knowledge for designing image systems intended for consumer photography.
- Seeing
- Physiological optics
- Retinal encoding
- Human wavelength encoding
- Image quality metrics
When designing a digital camera, how good does it need to be? The answer depends on the intended use case. If the images are for a person to see, the camera’s design must be guided by the capabilities and limits of the human visual system. This principle has profound consequences for engineering.
Human vision resources
- Glossary: Human Vision: A reference table and guide defining fundamental terms—including visual angle, cycles per degree (\(\text{cpd}\)), diopters, rod and cone photoreceptor properties (L, M, S cones), photopic/scotopic regimes, and the contrast sensitivity function (CSF).