Shulou(Shulou.com)11/24 Report--

In recent years, the development of mobile phones is getting faster and faster. in addition to the continuous improvement of hardware configuration, there is another phenomenon that many people cannot understand, that is, the camera whose skill tree is getting more and more crooked.

For example, before this type of mobile phone, there is only a quiet camera behind it, there is no play at all. And now mobile phones, "two cakes", "three cylinders" and even "bath tyrants" emerge one after another. What is the use of these cameras that make mobile phones more and more "ugly"?

Light L16 16 digital camera, are you scared? | | what are the two cameras on the theverge.com dual camera phone? " To explain the reasons for the three and four shots, we have to start with the double shots. Although there are a wide variety of mobile phones that support dual cameras on the market, most of them are a main camera with an auxiliary camera. According to the focus of the photo, there are four ways to match them:

Color camera + black and white camera

Color camera + color (depth of field) camera

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

Color camera + depth camera

Among them, the first three are the most common matching methods on mobile phones. The essence of these three imaging methods is to process and superimpose the images captured by the two cameras, so as to achieve different imaging effects. For the accuracy of image processing, the difference between the two pictures should not be too big, so the two cameras of all dual-camera phones are very close.

Color camera + black-and-white camera: to achieve a clearer night scene.

Because the light is too dark in the night scene, the pictures we take are often dark and we can't see anything clearly. In order to make the photos taken in the night scene clearer, you need to increase the amount of light input, there are three ways to increase the amount of light input: increase the aperture, prolong the exposure time, and improve the sensitivity of ISO. At present, the aperture on most mobile phones is not adjustable. Although extending the exposure time can increase the amount of light input, it will bring jitter problems, although most mobile phone manufacturers are equipped with optical anti-shake function, but the optical anti-shake ability is limited after all.

The digital camera is essentially photoelectric conversion, improving sensitivity, which is equivalent to multiplying the optical signal into an electrical signal, and the electronic noise may also be recorded as a normal signal, which will increase the noise on the photo and make the picture unclear.

When the physical method of increasing the amount of light encounters a bottleneck on the mobile phone, we need to find out the power of the algorithm.

First of all, I would like to introduce a concept here: Bayer filter (Bayer Filter). At present, the image sensors of digital cameras, scanners and other equipment mostly use it to make color images. When we take pictures with a color camera, the natural light will be filtered by the Bayer filter, and the color image will be generated after a series of complex arrangements and algorithms. In this process, the light is lost. On the other hand, the black-and-white camera is not equipped with a Bayer filter, which will allow all the light to pass through, resulting in a higher amount of light input, clearer images and more details.

Under the condition of night scene, a better picture can be obtained by fusing a clear black-and-white image with a color image.

Color camera + color (depth of field) camera, bring beautiful background virtual.

What is the depth of field? When we take pictures, there is a clear range between the front and rear of the object (focus), which is the depth of field. When shooting a portrait or a close-up, the SLR falsifies the background and highlights the subject by adjusting the depth of field.

Virtual close-up of the background | this is achieved by adjusting the lens aperture of the DSLR provided by the author. As we have said earlier, the aperture on most mobile phones is not adjustable. So if we want to shoot a close-up of a portrait with a virtual background, we encounter a bottleneck on the mobile phone again, so we once again find out the power of the algorithm.

First of all, we do an experiment, close one eye, hold a pen in each hand, keep the two pens horizontal and equal to the height of the eyes, and then touch the tips of the two pens. Do you often find that the tips of two pens can not touch each other, but if both eyes are open, the tip of the pen can always touch each other accurately? The triangulation method is used in this experiment. The triangle location method uses two or more detectors to detect the target in different directions, and then uses the principle of trigonometric geometry to determine the position and distance of the target.

The virtual effect of the simulated SLR of the dual-camera mobile phone is the triangular positioning method. First of all, two cameras are used to determine the distance between the objects in the photo before and after the space, that is, the depth of field information; then the objects in the photo are divided into planes according to the depth of field information; finally, the corresponding plane is selected according to the needs, such as the portrait mode. Select the plane where the portrait is located, and then virtual to other planes, you will get a clear portrait with a virtual background. Of course, this virtual process also needs a strong algorithm to guarantee, we will not repeat it here.

Color (wide-angle) camera + color (telephoto) camera to provide better zoom ability.

What is wide angle and telephoto? The wide-angle lens has a short focal length and a large viewing angle, which is suitable for shooting scenes with a large area; the telephoto lens has a small viewing angle but a large focal length, which is suitable for shooting objects with a long distance. In popular terms, the wide-angle shot has a wide range and the telephoto shoot has a long distance.

The way for a SLR lens to change the focal length is optical zoom, which is to change the viewing angle and focal length by moving the lens in the lens back and forth. In order to achieve the purpose of zoom in this way, it is necessary to leave room for lens movement in the lens, so the volume of the general zoom lens is very large. Limited by the size and thickness of the phone, optical zoom has encountered a bottleneck on the phone.

This kind of coquettish operation of the mobile phone can not come | reddit is wrong! Some people may ask, in the past, my phone with only one camera could also zoom. This has to mention another way of zoom: digital zoom. The so-called digital zoom only magnifies part of the viewfinder, which explains why the picture of the previous single-camera phone becomes blurred after zooming.

This combination of cameras can achieve a better zoom effect and obtain clearer zoom photos by switching cameras and merging photos taken by the two cameras. This method is still not a real optical zoom, but the zoom effect is much better than that of a single camera.

Color camera + depth camera: can be used in face recognition, AR, 3D space measurement and other fields.

A depth camera is a camera that can measure the physical distance between the object being photographed and the lens. This combination method can obtain real three-dimensional images, and it will have a wide range of applications in the future, but there is less use on mobile phones at present, so it is not introduced too much.

So back to our initial question, why are there more and more cameras on mobile phones?

The principle of three-camera and four-camera is the same as that of double photography, except that on the basis of double photography, 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 kind of mobile phone photography is very good, which is very flagship feeling, more conducive to the promotion and sales of mobile phones.

Can mobile phones replace DSLRs? In recent years, the pixels of mobile phones are getting higher and higher, even reaching 100 million pixels, so many people say: "mobile phone photo camera", "hanging SLR" and so on. So can mobile phone photography really replace the DSLR? Is the pixel as high as possible?

The answer is: No!

This is about to bring out an important role: image sensor. An image sensor is a photosensitive element that converts the light signal received by the camera into an electronic signal. For photography equipment, it is equivalent to human eyes. Therefore, the quality of the image sensor can basically determine the quality of the photo. However, limited by the current technology, the size of the image sensor on the mobile phone can not be magnified.

As we usually say, a camera with 2000 megapixels means that there are 20 million photosensitive points on the image sensor. When taking a picture, the photosensitive spot records the light, shade and color of the light, generates a pixel, and finally all the pixels form a picture. The more pixels (photosensitive points), the clearer the picture will be when enlarged.

In this way, it seems that the higher the pixel, the better, but not necessarily. For the same image sensor, we can divide it into 20 million photosensitive spots and 40 million photosensitive spots. In this way, although there are more photosensitive spots, the area of each photosensitive spot is smaller, so each photosensitive point can receive less light, which will affect the quality of the picture.

Therefore, the most important thing in taking a good picture is the amount of light signal that the image sensor can accept and process. There is a popular saying in the photography circle that the image quality of a large-size image sensor should be crushed to death of a small-size image sensor. As for why the phone can't replace the SLR, this picture of the phone's image sensor P to the SLR (the one in the red circle is the phone's image sensor) can be said to be very essential.

Comparison between image sensor and DSLR of mobile phone | Fuji Digital

The comparison of these "eyes" is even more obvious than that of Li Jung-hao and Rainie.

reference

[1] https://snapshot.canon-asia.com/article/zh/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

This article comes from the official account of Wechat: fruit Shell (ID:Guokr42), author: half of it, Editor: da Lin, Review: steed

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