The allure of a picturesque natural setting—perhaps a tranquil brook flowing beside a lush forest, with sunlight filtering through the delicate green leaves—can be captivating. Moments like these can feel enchanting, and many photographers strive to immortalize them. However, upon reviewing the images later, they often find a jumble of branches and greenery instead of the magic they experienced.

The phenomenon has a scientific basis: the captivating scene exists solely in our minds and cannot be captured by a camera. For centuries, artists have explored and enhanced their methods of translating the three-dimensional world onto a flat surface. Techniques such as perspective, shading, focus, color, atmospheric effects, recognizable objects, motion parallax, and stereopsis—our stereo vision—are all ways to convey depth. While the first six can translate into a two-dimensional representation, the last two require more complex interaction with our perception.

In environments like the edge of a forest, other spatial perception cues are often minimized, making stereo vision the primary means of interpreting space.

The discovery of perspective as a formal technique dates back to the early Renaissance. Although isometric drawing was utilized in ancient Rome and Asia, the notion of vanishing points was established by artists like Brunelleschi in the 15th century. An early example of perspective illustrates this concept:

In this work, lighting is secondary; the spatial structure is defined through lines and planes, constructed with precision. The artist’s enthusiasm for the technique is palpable, allowing viewers to instinctively perceive depth, even in a rudimentary form.

Shading enhances the representation of architectural spaces. While minimal shading is present in the earlier example, effective lighting and shadowing are crucial for depth perception across various distances, as seen in Leonardo’s Annunciation.

Focus may be a learned technique for suggesting depth, emerging with the advent of photography and film. Unlike classical painting, where focus plays a minimal role, in photography, it significantly shapes our perception of depth.

Color serves as another indicator of spatial depth; photographers understand the importance of aligning red and blue light on the same plane. Misty blue backgrounds enhance the sense of distance, while vibrant colors draw attention to the foreground, though this may also be a learned artistic convention.

The effects of atmosphere—such as smoke or haze—create layers within an image that suggest depth, which we recognize from our experiences.

Familiar objects in a scene can establish scale, effectively grounding the viewer. A photographer might place a person in a bright outfit within a vast landscape to convey size.

Motion parallax provides a unique depth perception that engages the brain. Although it doesn’t apply to still images, it is experienced in real life as landscapes shift past our view, triggering a depth response.

Stereopsis, or the sensation of depth from the different perspectives of our eyes, is so familiar that we often overlook it.

This image demonstrates how to perceive stereo pairs without specialized equipment. By focusing on the distant horizon, one can merge the two images in the brain, creating a stereo effect.

My interest in depth perception has deepened through art history studies and scientific literature. Interestingly, stereo perception varies among individuals with normal vision. While some perceive depth vividly, others, like Rembrandt, may have experienced limited stereo vision. Research has suggested that he struggled to focus both eyes on the same object, indicating varying experiences of depth perception among artists.

Moreover, the effective range of stereo vision extends much farther than previously thought, with some studies indicating its usefulness at distances up to about 500 feet, or even a kilometer, contradicting earlier assumptions about a mere 20-foot limit.

This explains why some natural and urban landscapes are particularly captivating. Standing in a space surrounded by dramatic forms allows one to experience stereo vision at its fullest. Closing one eye diminishes this experience, reducing vast views to mere flat representations.

Upon reflection, locations like a forest's edge often lack perspective cues. The absence of dominant objects and color variations, coupled with bright light, leads to a direct perception of space, devoid of indirect hints.

This awareness extends to our everyday experiences, not just in striking locations. Stereo vision is one of many ways we perceive depth, reinforcing our understanding of space through other cues. Its effectiveness becomes most pronounced when it stands alone or is experienced from a distance.

Some of my favorite experiences of depth include walking across the George Washington Bridge or gazing over the Seine in Paris. Experiencing these moments at night, illuminated by artificial light, makes them even more memorable.

What does this mean for photographers? It does not imply a need to revert to obsolete 3D photography methods. Despite periodic attempts to commercialize 3D media, such as television and films, they often fail to resonate with audiences. Instead, it’s crucial to recognize and consciously apply various techniques to convey a sense of space on a flat surface.

Artists like Fan Ho have mastered the art of depicting space, employing subtle visual cues to achieve depth.

Ultimately, the direct perception of space evokes a sense of our own mortality, as we realize these experiences are transient. In contrast, photographs—while seemingly flat—allow us to revisit moments, offering a sense of control over our memories.

So, when you find yourself immersed in a beautiful environment—whether it’s along the Seine or elsewhere—don’t expect too much from your camera. Simply enjoy the moment; it exists in your mind.

Notes and References

The body of literature surrounding depth perception is surprisingly limited, despite its significance. Many studies are inaccessible due to academic paywalls. Here are a couple of informative papers worth exploring:

Binocular depth discrimination and estimation by Allison R. S., Gillam B. J., and Vecellio E. (2009). Journal of Vision, 9(1):10, 1–14, doi:10.1167/9.1.10. [PubMed] [Article] [CrossRef] [PubMed]

Stereoscopic perception of real depths at large distances, by Stephen Palmisano et al., June 2010.

This article discusses Rembrandt's alleged difficulty with stereo depth perception and suggests that a lack of stereopsis might benefit artists by allowing them to focus more on their work without distraction.

Famous Paintings Can Reveal Visual Disorders; Neural pathologies have shaped great art throughout history by Susana Martinez-Conde and Stephen L. Macknik, Scientific American, March 1, 2015.

My eight methods for detecting depth in images are not exhaustive; other learned cues, such as how objects cluster near the horizon, also apply to two-dimensional images like photographs.