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Mi Max 3

[Discussion] [How it Works #6] Camera in smartphone, and how it works!

2019-05-21 10:50:18
836 42


Dear Mi Fans!

This is a new series about all the components of your smartphones and how it work inside your device!
Almost all modern smartphones are equipped with Camera. But not everyone knows how itit work! Today you'll know more about this smartphone detail.

Smartphone cameras have recently made a big leap forward, compared to cameras 10 years ago. Many devices allow you to take pictures at night without a tripod with previously unattainable quality, remember what photos you took from your first smartphone with a camera, today you can manually adjust the shutter speed, ISO and other parameters, and some even shoot in RAW format. But what exactly determines the technical quality of photos? Surely, many will immediately remember the glory megapixels - and they will be right. But only partly - therefore, I propose to talk about cameras in smartphones. Understand the principles of operation and various characteristics. You will learn about why the phrase “more megapixels better quality” does not always work, and let's look at the structure of the main elements of a smartphone’s camera. The first thing you need to know is what parts does the camera itself consists of and how it works.
Common camera device!

The camera of the smartphone from the side looks like a plastic "peephole", but in fact it is a complex multicomponent system of lenses and other auxiliary components. It is based on the matrix and lens. In addition to these devices, there is often complex mechanics for image stabilization and autofocus, laser range finders, RGB sensors and various types of flashes, single-color and two-color. The shutter in smartphones is electronic, not mechanical, and therefore the favorite “click” of the shutter should sound the dynamics of the smartphone.
The overall quality of photographs in the broad sense of the word (color, detail, dynamic range, etc.) Most closely matches the model of the camera matrix installed in the smartphone and interfaced with the lens system. The resolution of images and the amount of noise in night photos, as well as whether the photo is illuminated or in low light, depends on the matrix. From the characteristics of the lens - the viewing angle, as well as sharpness and other parameters of the resulting image after shooting. In turn, the technology used in the autofocus smartphone is determined by the speed and accuracy of the focus. This is especially important to prevent misfires at night when photographing moving objects.


Matrix: principle of operation
If the image in the old camera was fixed with a photosensitive film, then a photosensitive matrix was installed in its place in the digital camera. This component is called so because it is a rectangular element with millions of tiny photosensitive diodes located on it.


By themselves, these photodetectors are not able to perceive colors, so it are covered with a filter of one of the primary colors: red, green, blue (RGB color model). Thus, the light flux first passes through the lens, then shines through an array of color filters (usually a Bayer filter), and only then reaches the photodetectors.

  

Each photosensitive element perceives ⅓ color information or if it is reduced to a percentage, then ~ 33%, and ⅔ that is ~66% is cut off by a filter. Information about the missing color is “drawn out” from the neighboring photosensitive cells. After that, the processor calculates the color data based on the readings of the surrounding cells and only after that it forms the final value of the color pixel. Those. several matrix photodiodes are involved in the formation of one pixel, but not in one case. All these elements are so small that it is visible only under a microscope. One million of these pixels make up one megapixel. Accordingly, the more megapixels, the more detailed (consisting of more points) will be the final image file.
Historically, CCD technology was considered one of the best in quality, but for a number of reasons, CMOS technology captured a large market share. Smartphones also use a variety of CMOS technologies. This type of matrix has a number of functions that are most important for mobile gadgets: CMOS arrays have low power consumption, allow you to place amplifiers inside a pixel (which improves quality in low light), cheaper to manufacture, provide high speed operation during operation. image formation and when viewing in real time.

Matrix: the size of the "grain"
In addition to the number of pixels on the matrix, the actual quality and "purity" of the generated digital image strongly depend on the physical size of the matrix and the physical size of each pixel separately. The larger one pixel (the bold pixel is often said), the better the photosensitivity. And the larger the physical size of the matrix, the easier it is to place large enough pixels at some distance from each other. This allows you to reduce parasitic flow of charges - "pickups" from neighboring pixels, due to which interference and radiation, called digital noise.
Smartphones usually have a small matrix, the area of ​​which is about 50 times smaller than that of a full-frame SLR camera. Increasing the size of the matrix in smartphones is very difficult - too little space in a thin compact case. Excessive “megapixel” with a small matrix leads to a decrease in the size of the pixels, that is, to a decrease in sensitivity and an increase in the noise of images.
In other words, you cannot judge a camera by the number of megapixels. If you want less noise and higher quality in night shots, pixel size is more important. There are technologies that combine several pixels into one. This allows by reducing the resolution to increase the sensitivity of the matrix when shooting in low light conditions. Information about the size of the pixels is easy to find on the Internet: you first need to find out the model of the photosensor installed in the smartphone. and then its specifications. For a smartphone, a pixel size of 2 microns is considered large, and a small one is about 1 micron. In the context of physical limitations, manufacturers have made efforts to improve the image quality thanks to new technologies. Therefore, a large number of megapixels are not always bad - modern matrices with applied technologies allow to isolate pixels from each other, high-quality lens system and good software optimization, are quite capable of accepting photos at night, as well as making good and detailed images in bright sunlight. The same “megapixel” can be useful for shooting video. Often, it is these matrices that allow you to shoot in 4K with high FPS.

Lens: focal length, sharpness and chromatic aberrations (CA).
Often, the matrix for smartphones are supplied by the manufacturer already bundled with a specially selected lens. But it also happens that the developer of a particular smartphone decides for itself what “glass” to put in front of the matrix. This (as well as image processing algorithms) explains the fact that, depending on the model of the device, the same matrix may manifest itself in completely different ways.
As in the cameras of smartphones, albeit in a reduced and simplified version, the lens is not just a single glass, but an optical system from a group of lenses, with which the maximum image quality with minimal distortion is achieved.
In general, the quality of the final image depends very much on the quality of the lens system. For example, if a good lens is installed in front of a good matrix that simply cannot “resolve” the sensor, then the image detail will not be increased, no matter how many megapixels. Image files will be huge in size with a formally large number of pixels, but the clarity of the photos will not increase.
The different sharpness of the lenses can vary considerably across the entire field of the frame, and the problem of chromatic aberration (CA) is also often present. If the smartphone has good optics, then the test shots will not have “soap” in the corners of the frame, and when shooting, for example, thin branches of trees when illuminated (black outlines against the bright sky) color halos will not appear (the same CA).


Of course, focal length and aperture size are important parameters in optics. At the moment, smartphones always use wide-angle lenses, since a small matrix has a large framing ratio (the ratio of the size of the matrix of the smartphone to the historically “normal” 35 mm frame in the photo). For example, a super-wide 4-mm “peephole” on a smartphone will roughly correspond to a 30-mm lens with a focal length mounted on a camera with a full-frame sensor or a classic 35 mm film. Basically, from the point of view of the focal length among smartphones, there is no significant difference: almost all devices have wide-angle optics, which allows to fit almost everything into the frame, without departing from the objects of shooting for a long distance.  Some smartphones are equipped with especially wide-angle lenses with an increased viewing angle of up to 135 degrees, which is not very good in photos. This optics allows you to cover a large stage, but introduces unwanted geometric distortion of the objects being shot. For example, an excessively wide angle on the front cameras distorts the proportions of the face and causes a fisheye effect. It's worth noting, that most smartphones today have fixed-focal length optics, there are models, albeit with a small, but full-fledged optical zoom.
Lens: aperture
Another important lens parameter is the f-number (F).This value is inverse to the value of the relative aperture of the lens, that is, the ratio of the "pupil" to the focal length of the lens. Smaller the f-number, the larger the hole. The lens will miss more light, the matrix will have to “amplify” the signal less. So, all other things being equal, there will be more opportunities to make high-quality pictures at night (when there is little light) with less noise.


The diaphragm number also largely determines the possibility of obtaining a popular “Bokeh” effect - blurring the background. The degree of background blur in the pictures is affected not only by the aperture, but also by the size of the matrix and the focal length of the lens. In short, the larger the matrix and aperture (the smaller the F number), the longer the lens, the more opportunities to blur the background strongly when shooting a larger object. On smartphones, because of the miniature matrix and wide-angle lenses “truly”, the background is blurred only when macro shooting small objects like flowers, figurines, etc. To photograph a person in full growth or at least to the waist and at the same time to blur the background is only possible for cameras with a large matrix and portrait lenses with a large aperture. In smartphones at the moment, blurring when shooting large objects is achieved only with the help of “imitation” programmatically on some devices with “dual” cameras.

From the point of view of the buyer, you need to know that most of the cameras in a smartphone have f/2 and f/2.2 aperture values. Some cameras boast the best rate - f/1.8 and f/1.7.

In general, shooting with a fully open aperture is not always optimal in terms of image detail, but on smartphones, due to technical features, it is still not adjustable. So in the context of the current state of affairs in the world of smartphones, it is better to choose a device with a lens with a larger aperture. Such lenses, other things being equal, will provide better opportunities for night shooting and are able to more blur the background during macro photography.

Lens and electronics: focusing systems
The main camera doesn’t have autofocus today, except in quite budget smartphones, although its absence among the front-facing cameras is still not uncommon. When the camera is not equipped with autofocus, the lens of the device is set to "infinity". This allows you to photograph general plans and various objects at a great distance, but makes it impossible to focus at close range.

The autofocus system is passive and active.
Passive - relies on electronics and image analysis, but such a focus does not know the exact distance to the subject.
Active - uses a variety of sensors and is able to measure the distance to an object in order to properly focus on it.

So, the first system is “contrasting” autofocus, which most smartphones have in their cameras.


When you point the camera at a person in the background of a light wall, the device will detect the contrast, for example, at the border of the clothes and the wall, and focuses on this basis. In this case, the lenses will move as long as the electronics compares the contrast at their different positions. As you might guess, such a system is not very perfect: it does not always work quickly, it is better suited for shooting static objects, it can make mistakes or even refuse to work in poor light when there are no contrasting objects in the frame. Which leads to bad photos and videos. The active system with the help of additional sensors calculates the distance to objects in order to more accurately and quickly catch the focus on them. For example, smartphones with a phase focusing system use additional sensors located closer to the edges on the matrix to analyze the “forked” image of objects, constantly adjusting the focus so that the two projections merge into a single whole (it are in phase).


This system is good in the first place at high speed, it helps to focus on fast moving objects in daylight, but at the same time it can collapse at night.

Video
Speaking of shooting a video, the resolution is called as the main characteristic. For example, HD is 1280 * 720 pixels, Full HD is 1920 * 1080 and 4K is 3840 * 2160. However, just like “megapixel” when photographing, high resolution does not necessarily mean an outstanding result and super video quality. On the video, as in the photo, affect all the previously listed parameters, the matrix and the quality of the lens. But besides this, video shooting on modern smartphones strongly depends on the central processor of the gadget. The fact is that besides the resolution (HD, Full HD, 4K), the video has a parameter known to many that is fps (frames per second), as well as the bitrate. The number of fps makes the video smooth (the larger the number, the smoother the video will be). The quality of the picture depends on the bitrate during recording, which will be fixed inside the indicated resolution, no matter if it is Full HD or 4K.


Only smartphones with a powerful processor can record video at the same time with a high bit rate, high FPS and 4K resolution, as it must calculate the parameters for each of the millions of pixels instantly.

It also happens that the camera module installed in the gadget supports better video shooting, but due to processor limitations, the manufacturer has to artificially reduce image settings. This sometimes occurs. In addition, if you plan to use your smartphone for video, you should avoid devices prone to overheating and throttling (lowering the frequency of work) - such devices simply will not allow you to shoot video for a long time and will turn off the camera after 8-15 minutes of video recording, or even if filming is supported 4K, then simply for a very short period of time (6 minutes at most) so as not to overheat the processor and it does not fail, it is fraught with a complete replacement of the motherboard.

Identify the lack of capacity for high-quality video encoding is obtained by test shooting at maximum resolution (4K) with maximum quality settings in the semi-dark. If fps is sharply reduced in video, it means that the CPU power is not enough for full-fledged shooting in difficult conditions. We'll have to lower the resolution or completely abandon the purchase of such a smartphone.

Findings!

Of course, there are objective limitations associated with the dimensions of smartphones, which makes it impossible to install a large matrix or complex optics in them, as everyone wants to make a smartphone thinner and lighter, but many technologies and software processing do a lot today. So, knowing the basic parameters of the cameras, evaluating the hardware of the device and checking the test shots of the smartphone you like, you can make an informed choice. And if from the very beginning you do not put extra hopes on smartphones and understand the strengths and weaknesses of such devices, it will not disappoint.

Thanks to all, And Administrator Elaine2046!

[How it Works #4] Type of Touchscreen and How it Work!
[How it Works #5] Type of Display and How it Work!


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2019-05-21 10:50:18
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News Reporter

ᎮᏒᎥᏁፈᏋ | from Redmi Note 4X

#1

thanks for sharing nice article
2019-05-21 10:59:52

Grand Master Bunny

Seragios | from Redmi 5

#2

Thanks for information
2019-05-21 11:09:47

Pro Bunny

Erdinçer | from MI MAX 2

#3

Thanks for the info
2019-05-21 11:42:53

Master Bunny

1860bodo | from Redmi Note 5

#4

thanks for nice review
2019-05-21 12:18:57
Great Article !
2019-05-21 13:47:01

Device team

$huvo | from Redmi 4

#6

Nice thread
2019-05-21 14:48:21

Beta Team-Global

georan. | from Redmi Note 5 Pro

#7

thanks for sharing article
2019-05-21 15:05:24

Grand Master Bunny

Ian Adoe | from Redmi Note 5A

#8

nice info, thanks
2019-05-21 15:22:17
Thank you for your information.
2019-05-21 16:01:13

Advanced Bunny

Proteus8 | from Redmi Note 7

#10

nice article, well explained
2019-05-21 16:03:28
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