How the Lytro Camera Functions

Capturing the ideal photograph is both an art and a science. Back in the days of film, you had to ensure you had the correct lens, lighting, and type of film to capture the perfect shot. As digital cameras emerged, lens selection and lighting remained crucial, but familiarity with editing software became equally essential. The right tools allow you to adjust color balance, contrast, and other key elements of the image.

Even high-end cameras for professional photographers come with limitations. One of these is the focal point of any photograph. Imagine you’ve set up a shot where a tree branch is in the foreground and a person stands in the background. You adjust the camera’s settings so the person in the back is in focus. The tree branch in the front remains blurred, which you hope will create an artistic effect. You capture the photo.

Later, as you examine the image, you may feel uncertain. Perhaps it would have been more captivating if the focus had been on the tree branch instead of the person. Maybe the ambiguity would have made the photo even more intriguing. But you’ll never know, as you can’t change the focus after the photo is taken.

The Lytro camera solves this issue by utilizing specialized lenses and sensors to capture the entire light field of a scene. When you take a picture with the Lytro camera, you’re only just beginning. With the unique software that comes with the camera, you can adjust the focal point of your photo even after it’s been taken. Switching focus from the foreground to the background is as simple as a tap on your screen or a click of a mouse.

How does it function? To truly understand, let’s first explore how a traditional camera captures an image.

Understanding the Focus Challenge

At its core, a camera captures light. When you photograph a scene, the light reflected by that scene enters your camera’s lens. The lens bends and redirects the light to the recording medium. In a film camera, this medium is a strip of chemically treated plastic. In a digital camera, it's an electronic sensor.

As light passes through the lens, it bends and the rays converge at a single point. To keep the subject of your photo in focus, this point needs to land on the film or digital sensor’s surface. You can adjust where the rays come together by altering the distance between the lens and the medium. When you focus the lens, you’re essentially moving it closer or further from the rest of the camera.

The lens's curvature determines where the light will converge. A flat lens won’t bend light as sharply as a curved lens. That’s why light will focus farther from a flat lens than it will from a rounded one. Depending on what you’re photographing, the right lens will ensure your subject is sharp and clear.

Traditional photography captures all the light that strikes an image, but no single setting on a conventional camera can let you change the focus after the shot. What you see in the final picture is what you’ve got. However, if you could record every individual light ray, preserving all the scene’s visual details, you could adjust the focus after the fact using specialized software.

This is the core principle behind the Lytro camera. It doesn’t just capture the total amount of light within a scene; it records the actual light fields.

Exploring Light Fields

When we observe a lit object, our eyes detect the light that bounces off of it. This light radiates in all directions—and if the object is transparent, the light passes through it as well. If you could isolate a single point in space within this illuminated scene, you’d see light rays crisscrossing through, moving in every direction.

This phenomenon is known as a light field. You can think of a light ray as having five dimensions. Three of these are the familiar spatial dimensions—height, length, and depth, or the x, y, and z axes. The remaining two dimensions relate to the movement of light along the ray.

The geometric distribution of light is called the plenoptic function. The term plenoptic is derived from the Latin word plenus, meaning full or complete, and optics, which refers to the behavior of light. To fully capture the light from a scene, a plenoptic camera would be required.

A true plenoptic camera is more of a thought experiment. Opaque objects block light—causing occlusion. To capture a light field, the camera and the photographer would need to exist at every angle around a subject simultaneously, without blocking any light. We haven’t yet figured out how to position a camera to capture every perspective or prevent occlusion. However, the Lytro camera mimics some plenoptic functions.

The device shares several similarities with a typical digital camera. It has a lens and an aperture that allows light to pass through. It also features a sensor that detects light. However, between the two, there is an array of microlenses. These lenses are significantly smaller than the main lens of the Lytro; for example, a prototype plenoptic camera, which preceded the Lytro, had microlenses that were 280 times smaller than its main lens [source: Ng].

The microlenses in the array guide light from behind the main lens to the sensor. The sensor captures the light field between the Lytro's lens aperture and the sensor itself. The resolution of the images depends on both the power of the sensor and the number of microlenses in the array.

Once the image has been captured, it’s time to process the data.

Simulating Depth

Picture a long table covered with various objects. You stand at one end, focus on the closest objects, and take a photo. With a standard digital camera, the closest objects will appear in focus, while the more distant ones will be blurry and less defined in the photo.

At first glance, a Lytro photo might appear just like a regular one. However, if you decide you want a different part of the image to be in focus—perhaps those interesting toys you placed at the far end of the table—the focal point can easily shift.

The Lytro’s sensor can produce different images based on the light field captured within the camera. While a traditional camera’s focus is fixed at the time of shooting, the Lytro offers flexibility. You can adjust the focal depth of a Lytro image after you’ve taken the photo.

In a physical camera, focusing involves adjusting the lens and aperture, moving them closer to or farther from the sensor. For a Lytro image—the file format is called a Light Field Picture (LFP)—the software generates a virtual lens and sensor. This simulation mimics what would happen if you physically adjusted the focus on a traditional camera, with the virtual lens shifting in relation to the virtual sensor.

This process is powered by a complex set of algorithms. The light captured by the camera acts as data, and these algorithms guide the Lytro software in recreating the effect of a physical camera’s focus change. Without the light field data, the Lytro wouldn't be able to switch the focus effectively.

The company offers Lytro Desktop, a software tool for managing and editing Lytro photos on your computer. In the future, the camera may allow you to capture photos with an extended depth of field, enabling you to keep both foreground and background objects in focus simultaneously. Extended depth-of-field algorithms combine the sharpest elements from each potential shot you could take with the Lytro camera. It’s as if you were capturing multiple photos with different focal points, then merging the focused sections to create a unified image.

Living Pictures

Lytro refers to their Light Field Pictures (LFP) as 'living pictures' because they allow viewers to alter the focus after the photo has been taken. This interactive experience is made possible by sharing the images through Lytro Web, a platform that enables others to adjust the focus as they explore your photos.

Alternatively, you can store your LFP images on your computer and view them using the Lytro Desktop software. This software provides you with the same focus-shifting capabilities, allowing you to change the focal point of any image captured with the Lytro camera, at any time. While LFP files hold all the light field data from your pictures, the software contains the necessary instructions to modify the focus settings.

One downside of light field photography is the large file sizes. Because capturing the full light field data requires substantial storage, a typical LFP file is around 16 megabytes. In comparison, a standard JPEG image on the Web might only be around 30 kilobytes or even smaller.

Another limitation is the inability to share LFP files outside of the Lytro Web platform. To share an LFP image, you must first upload it to Lytro Web, and then you can share the link with others, giving them access to the interactive focus features.

While it's possible to convert an LFP file into a JPEG, there's a tradeoff. JPEGs can't retain the living picture functionality, meaning you lose the ability to change the focus. When you export an LFP as a JPEG, you first need to select a focal point, and after that, the image becomes a standard, uneditable digital photo.

Could light-field photography eventually replace traditional photographic skills like composition and focus? For now, the limitations of the Lytro camera suggest that it won’t fully replace the expertise and artistic touch that photographers develop over time. However, in the future, these cameras might make it possible to simply point, shoot, and adjust the focus later with ease.

Here's an example of a Living Picture. Captured by Lytro community member hanlin, this image allows you to interact with it by clicking on the Eiffel Tower in the background to bring it into focus, or by clicking on the model in the foreground to shift the focus back.