Signal Processing - September 2016 - 24

Lens-Based Cameras

Examples
DSLR Camera
Microscope

Captured Image

Sensor

Lens

Telescope

(a)
Lensless Cameras

Reconstructed Image

Mask Sensor

Examples
Lensless Compessive
Imaging [11]

Captured Data

Wide-Field On-Chip
Microscopy [24]

Diffraction Grating [16]

FlatCam (Second Prototype)

40 µm

Fiber

(b)

Figure 1. Lensed versus lensless imaging. (a) An illustration of a lens-based camera, where a lens maps the scene onto a sensor to form a clear image.
A few examples of lens-based systems are shown. (b) The process of capturing an image using a lensless camera. An additional step of computation is
required to reconstruct a clear image from the muddled sensor data. A few examples of lensless cameras [11], [16], [24] and our prototype based on [31]
are also shown. (Figure adapted with permission from Macmillan Publishers Ltd: Nature Methods [24], copyright 2012.)

the sensor. Coded aperture cameras improve the light efficiency
using a mask with an array of pinholes. The sensor measurements become a superposition of the images formed by each
aperture, and the computational recovery algorithm's task is to
reorganize the measurements to recover the image.
There are many benefits to going lensless;
■ Scalable fabrication. Lensless cameras can be directly fabricated using traditional semiconductor fabrication technology. For example, a multiple-aperture mask can be fabricated
either directly in one of the metal interconnect layers or on a
separate wafer thermal compression that is bonded to the
back side of the sensor, as is typical for back-side-illuminated image sensors [1]. Thus, lensless cameras can benefit
from all of the scaling advantages of semiconductor fabrication, resulting in a low-cost, high-yield, high-performance
device. In contrast, conventional cameras require inefficient
post-fabrication assembly of the lens system.
■ Thin form factor. Since the standoff distance between a
multiple-aperture mask and the image sensor array need only
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■

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be a few tens to hundreds of microns, an entire lensless camera can be only a few tens to hundreds of microns thick-
resulting in potentially the thinnest cameras ever produced.
Wavelength scaling. Lensless cameras have been used for
X-ray, gamma-ray, and astronomical imaging for decades.
Lensless imaging in the visible, short-wave infrared (SWIR),
and thermal wavebands is relatively new. Moreover, the technology can also be expanded to the mm-wave, terahertz, and
other bands with minimal modifications, providing
unmatched spectral flexibility.
Low cost. While the cost of high-resolution cameras has
fallen rapidly in the visible range, it remains high outside the
visible range (e.g., infrared). One reason is that lenses for
these wavelengths must be manufactured using expensive
materials. By doing away with lenses and the need for postfabrication assembly, lensless cameras promise significant
cost reductions for imaging outside the visible spectrum.
Nonplanar geometries. Lensless cameras can be adapted
to arbitrary sensor geometries, including not just planar but

September 2016

Table of Contents for the Digital Edition of Signal Processing - September 2016