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In optics, Multi aperture represent a technology that shot multiple images for the same frame.

introduction


A single aperture constructed of a lens and a sensor. Multi aperture is a system that made of multiple number of lenses and sensors in a compact manner, in a symmetrical array. Pixels sizes remain the same, and each aperture acquire a complete image. The multi aperture has various abilities, for example: increase resolution, dynamic range and frame rate. Moreover, it assists decreases noises as RTS and dark current.

revolution in the the phone field
In the last few years, a revolution has begun in the smartphone field. Dual cameras, that work together, by using diffrent methods of the camera, the phones can reach high levels of accuracy in zoom, in both photo shooting and video filming.

In the new cameras, two images are taken, a wide one and a telephoto one. In the first stage, the camera produce a depth image, which can be fixed by calibration parameters. Afterwards, the image is getting through a last repair of blurriness, and a perfect photo is accepted.

The vertically shooting method
a shooting of an image or a video, even under difficult circumstances, a high quality picture is taken. A phone which has 2 apertures, one with wide lens, and the other has telephoto lens with thin field. Their combination provides 2 zoom values, - usually x1 or x2.

thin camera
In a thin camera the folded method is applied. In a zoom cameras, that have telephoto lens, tend to increase the z-highet, but in this method a z-height is only few millimetres long. The concept combine wide cameras module, and a Tele photo. A tele camera is designed so the light gets in through a prism, that folds the light, and leads it through a barrel that lens are set in it, till the light reaches to sensor vertically.

An OIS combined with the folding method
An OIS (optical image stabilization) method, shift the two axes that the lens are stabled on in the barrel. OIS ,ethod combined with the folding one, when the lens are vertical to the surface of the device.

further information


M pixel from every aperture are regarded as a sub-pixel, and they represent a large pixel whose area is M times larger than that of a single aperture counterpart Number of pixels for a duplicated image, in a multi aperture camera is as many as N*N, even though the number of pixels is actually M*N*N.

For a single aperture, an aberration can be fixed by adding more lenses to the camera. The extra lenses increase the weight of the camera significantly. In contrast, multi aperture has a synthetic f-number, this way it will allow high focus and light weight.

$$f_s={f_o \over \sqrt{m} }$$ In case the image is too dark or too light, or there are some blind spots, fabrication errors are made, and damage some pixels. In multi aperture a defective pixel can be removed without using interpolation, as it done in a single aperture.
 * $$f_0-f_{number}$$of the original lenses
 * m- number of pixels for a sub-pixel

In multi aperture, there are many pixels (N*N) for an identical objective point, and in case there is a defective pixel for a single aperture, the other apertures can calculate it.

Selective averaging


In multi aperture imaging pictures system, N*N images are taken for a single picture simultaneously. Even though, there are different values for an identical objective point, because of various noise because of the pixel amplifier and the ADC which added to each of them.

$$S_m^2={1 \over m^2}\sum_{i=1}^m \displaystyle\sigma_i^2$$ $$(1\le m \le N^2)$$
 * the number of the selected apertures-m
 * $$\displaystyle\sigma_i^2$$-variance of a single aperture
 * $$S_m^2$$-combination variance

A variance is calculated for each aperture, the apertures who has the high variance will be excluded. Therefore, pixels who have high variance will be excluded automatically. The selectiveness of choosing apertures, gives it the name selective averaging. Noise like RTS and shot noise that caused by dark noise, create high variance. In this method, apertures who have high variance will be removed, so the noise will not influence.

SNR
Calculate SNR for a single aperture, influenced by sensor noise and shot noise $$SNR_{SA}=20log_{10} {N_e \over \sqrt{\displaystyle\sigma_{sensor}^2+N_e}}$$
 * $$N_e$$-number of electrons in a signal
 * $$\displaystyle\sigma_{sensor}$$-variance of the sensor

In multi aperture, the SNR is accepted by selective averaging in m apertures

$$SNR_{MA}=20log_{10}{\sqrt{m}\cdot{N_e}\over\sqrt{N_e+{\displaystyle\sigma}^2_{sensor}}}$$

Abilities

 * 1) Facing different lightning- too light or too dark.
 * 2) Accurate depth and distance.
 * 3) Wide field of view.
 * 4) Very high optical zoom.

Uses

 * 1) 	Autonomous cars.
 * 2) AR/VR/MR headsets & 360 cameras.
 * 3) Survelliance & IoT cameras.
 * 4) Action Cameras & Drones.