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Apple invents 3-sensor iPhone camera with light splitting cube for accurate colors, low-light performance

An Apple patent published on Tuesday details a miniaturized iPhone camera system that employs a light-splitting cube to parse incoming rays into three color components, each of which are captured by separate sensors.


Source: USPTO


As granted by the U.S. Patent and Trademark Office, Apple's U.S Patent No. 8,988,564 for a "Digital camera with light splitter" examines the possibilities of embedding a three-sensor prism-based camera module within the chassis of a thin wireless device, such as an iPhone. Light splitting systems do not require color channel processing or demosaicing, thereby maximizing pixel array resolution.

Commonly found in prosumer video cameras, and more recently in handheld camcorder models, three-sensor imaging technology splits incident light entering a camera into three wavelengths, or colors, using a prism or prisms. Usually identified as red, green and blue, the split images are picked up by dedicated imaging sensors normally arranged on or close to the prism face.




Older three-CCD cameras relied on the tech to more accurately capture light and negate the "wobble" effect seen with a single energy-efficient CMOS chip. Modern equipment employs global shutter CMOS modules that offer better low-light performance and comparable color accuracy, opening the door to entirely new shooting possibilities.

Apple's design uses light splitting techniques similar to those applied in current optics packages marketed by Canon, Panasonic, Philips and other big-name players in the camera space. For its splitter assembly, Apple uses a cube arrangement constructed using four identical polyhedrons that meet at dichroic interfaces.




By coating each interface with an optical coating, particular wavelengths of incident light can be reflected or allowed to transmit through to an adjoining tetrahedron. Adjusting dichroic filters allows Apple to parse out red, green and blue wavelengths and send them off to three sensors positioned around the cube. Aside from RGB, the patent also allows for other color sets like cyan, yellow, green and magenta (CYGM) and red, green, blue and emerald (RGBE), among others.

Light splitters also enable other desirable effects like sum and difference polarization, which achieves the same results as polarization imaging without filtering out incident light. The process can be taken a step further to enhance image data for feature extraction, useful in computer vision applications.




Infrared imaging can also benefit from a multi-sensor setup, as the cube can be tuned to suppress visible wavelength components, or vice versa.

Tuesday's patent is an extension of a previously published Apple invention that uses mirrors and optics to achieve optical image stabilization without eating up valuable space. In such embodiments a foldable, or mobile, mirror redirects incoming light, bouncing it toward a rectangular tube that terminates with a cuboid light splitter. In between the mirror and sensor package are a series of lenses that can be operably moved for focus and zooming. Motors are applied to vary the mirror's angle to offset hand shake recorded by onboard sensors.




It is unclear if Apple intends to implement a light splitter into a future product, though the company is working hard to keep iPhone at the fore of ultra-mobile photography. For example, the latest iPhone 6 Plus includes an OIS system that produces sharp images even in low-light situations.

Apple's cube light splitter camera system patent was first filed for in 2011 and credits Steven Webster and Ning Y. Chan as its inventors.