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What are the two cameras on the dual camera phone?

To explain the reasons for three and four shots, you have to start with dual shots. Although there are various mobile phones supporting dual cameras in the market, most of them are a main camera with an auxiliary camera . According to the focus of the camera, there are four general matching methods:

Color camera + black and white camera

Color camera + color (depth of field) camera

Color (wide-angle) camera + color (telephoto) camera

Color camera + depth camera

The first three are the most common ways to pair your phone. The essence of these three methods of imaging is to process and superimpose the pictures taken by the two cameras to achieve different imaging effects. For the accuracy of image processing, the difference between the two pictures should not be too large, so all dual camera phones are close to each other .

Color camera + black and white camera: for clearer night scene photography.

Because the light is too dark under night scenes, the photos we take are often dark and can’t see anything clearly. If you want to make the photos taken in the night scene more clear, you need to increase the amount of light. There are three ways to increase the amount of light: Increase the aperture , Extend the exposure time , Increase ISO sensitivity . The aperture on most mobile phones is currently not adjustable. Although extending the exposure time can increase the amount of incoming light, it will bring about the problem of jitter. Although most mobile phone manufacturers are currently equipped with optical image stabilization, the ability of optical image stabilization is limited after all.

Digital cameras are photoelectric conversion in nature, which increases the sensitivity, which is equivalent to multiplying a multiple when the optical signal becomes an electrical signal. Electronic noise may also be recorded as a normal signal. This will Increase noise on photos , making photos unclear.

When the method of physically increasing the amount of incoming light encounters a bottleneck on the mobile phone, it is necessary to ask for the power of the algorithm.

First of all, here is a concept: Bayer Filter At present, most image sensors of digital cameras, scanners and other devices use it to make color images. When we use a color camera to take pictures, the natural light will be filtered by the Bayer filter, and after a series of complicated arrangements and algorithms, a color image will be finally generated. During this process, light is lossy . The black-and-white camera is not equipped with a Bayer filter. Let all light pass through , get a higher amount of light, the captured image is sharper, and more details are retained.

Under night scene conditions, a clear black and white image will be used as a reference to fuse with the color image to get a better photo.

Color camera + color (depth of field) camera brings beautiful background blur.

What is the depth of field? When we take a picture, the subject (focus) has a clear range before and after the scene, and this range is the depth of field. When shooting a portrait or close-up with a DSLR, blurring the background and highlighting the subject is achieved by adjusting the depth of field.

▲ Close-up bokeh | Photo courtesy of the author

SLR achieves this by adjusting the lens aperture. We have said before that the aperture on most mobile phones is currently not adjustable. So I wanted to take close-up portraits with blurred backgrounds and encountered a bottleneck again on my phone, so we asked for the power of the algorithm again.

First, we will do an experiment, close one eye, hold a pen in each of your left and right hands, keep both pens horizontal and level with your eyes, and then touch the two pen tips. Did you find that the two nibs often didn’t touch each other, but if both eyes were open, the nibs would always come together accurately. This experiment uses the triangulation method . The triangulation method uses two or more detectors to detect targets in different directions, and then uses threeAngular geometry determines the position and distance of the target.

▲ Triangulation method | csdn

The blur effect of dual-camera mobile phone simulation SLR is the triangular positioning method. First, use the two cameras to determine the front-to-back distance of the objects in the photo in space, that is, depth of field information ; then, according to the depth of field information, divide the plane of the objects ; Need to choose the corresponding plane. For example, in portrait mode, select the plane where the portrait is located, and then blur the other planes to get a clear portrait with a blurred background photo. Of course, this blurring process also needs a strong algorithm guarantee, so we won’t go into details here.

Color (wide-angle) camera + color (telephoto) camera, providing better zooming capabilities.

What are wide-angle and telephoto? The wide-angle lens has a short focal length and a large angle of view, which is suitable for shooting a large area of ​​the scene; a telephoto lens has a small angle of view but a large focal length, which is suitable for shooting objects with a long distance. Generally speaking, the wide-angle shooting range is large, and the telephoto shooting distance is long .

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▲ Photos taken with a wide-angle lens (above) and a telephoto lens (below) | Picture Bug Ideas

The way to change the focal length of a SLR lens is optical zoom, which is to change the angle of view and focal length by moving the lens in the lens back and forth. To achieve the purpose of zooming in this way, it is necessary to leave space for lens movement in the lens, so generally the size of the zoom lens is very large. Limited by the volume and thickness of the phone, optical changesJiao encountered a bottleneck again on his mobile phone.

▲ This kind of mobile phone can’t come | reddit

No! Some people may ask, my mobile phone with only one camera can also zoom! This has to mention another way of zooming: Digital zoom . The so-called digital zoom is actually just a part of the viewfinder. It is not difficult to explain why the previous single-camera mobile phone zoomed out the picture becomes unclear.

This combination of cameras can achieve better zooming effects by switching the camera and merging the photos taken by the two cameras to get a clearer zoomed photo. This method is still not true optical zoom, but the zoom effect is much stronger than a single camera.

Color camera + depth camera: It can be used in the fields of face recognition, AR, 3D space measurement, etc.

Depth camera is a camera that can measure the physical distance between the subject and the lens. This combination method can obtain real three-dimensional images, and has a wide range of applications in the future, but it is rarely used on mobile phones at present, so it is not introduced too much.

So back to our original question, Why are there more and more cameras on mobile phones?

The principle of three cameras and four cameras is the same as that of dual cameras, except that on the basis of dual cameras, adding more cameras can complete a richer combination .
In addition, the cost of the camera itself is not high. Through the combination of more cameras, mobile phone manufacturers can use a lower cost to create a mobile phone is very powerful , This is the flagship < / strong> feels more conducive to the promotion and sales of mobile phones.

Can mobile phones replace SLRs?

The pixels of mobile phones have been getting higher and higher in recent years, even reaching 100 million pixels, so many people say: “Mobile phones are better than shoulder cameras”, “SLRs” and so on. So Can mobile phones take pictures instead of SLRs? Is the higher the pixel the better?

The answer is: No !

This will require an important role: Image sensor . An image sensor is a light-sensitive element that converts a light signal received by a camera into an electronic signal. For a photographing device, it is equivalent to human eyes . So the quality of the image sensor basically determines the quality of the photo. However, due to the current technology, the size of the image sensor on the mobile phone cannot be enlarged .

We usually say that a camera with 20 megapixels means that there are 20 million light-sensitive spots on the image sensor. When taking a photo, the light sensitive point records the light and darkness and color of the light to generate a pixel, and finally all the pixels together form a photo. The more pixels (photosensitive dots), the sharper the picture will be taken.

It looks like the higher the pixels, the better, but not necessarily. For the same image sensor, we can divide it into 20 million photosensitive points, and it can also divide 40 million photosensitive points. In this way, although the number of light-sensing points is larger, the area of ​​each light-sensing point is smaller, so each light-sensing point can receive less light, and this will affect the presentation of image quality.

So, a good picture is taken, the most important point is the amount of light signals that the image sensor can accept and process. A popular phrase in the photography circle: Bottom-level crushing people means that the imaging quality of large-size image sensors must crush small-size image sensors. As for why the mobile phone cannot replace the SLR, this picture of the mobile phone’s image sensor P on the SLR (the red circle is the image sensor of the mobile phone) can be said to be very essence.

▲ Comparison of mobile phone image sensor and SLR | Fuji Digital

This “eye” is even more obvious than Li Ronghao and Yang Shulin!

References

[1] https://snapshot.canon-asia.com/article/en/lesson-5-what- is-iso-speed

[2] https://en.wikipedia.org/wiki/Bayer_filter

[3] https://en.wikipedia.org/wiki/Time_of_flight

[4] https://en.wikipedia.org/wiki/Charge-coupled_device [5] https: // en.wikipedia.org/wiki/CMOS