Structure of mobile phone camera and imaging principle of mobile phone camera

In the early 19th century, Sharp and the then Japanese communications operator J-PHONE invented the Sharp J-SH04. The Sharp J-SH04 has a camera function. On April 24, 2003, Sharp released the world's first megapixel mobile phone J-SH53. At one time.

With continuous breakthroughs and innovations in technology, new types of camera lenses have emerged like bamboo shoots. From the initial million to the current ten million, they have spent more than ten years, and the quality of photography has continuously entered a new stage. The most representative companies such as Huawei, Samsung, and Apple, Huawei started the lens and processing chip by leaps and bounds from the p6, the new design concepts continue to be applied in practice, such as years ago, or theoretical dual camera design, Samsung and Huawei have been mastered , have been used for the latest listing of mobile phones.

At present, the mobile phones on the market usually have front and rear cameras, generally in front of about 5 million, using from the shoot and video calls, rear generally is about 13 million, you can shine more clearly pictures and record clear video.

Phone camera composition

The mobile phone camera is mainly composed of the following parts: PCB board, DSP (for CCD), sensor (SENSOR), holder (HOLDER), lens (LENS ASS'Y). Among them, the lens (LENS ASS'Y), DSP (C, CD) and sensor (SENSOR) are the most important three parts.

PCB board

PCB board is divided into hard board, soft board, hard and soft combined board three (as shown below), CMOS can use any kind of board, but the CCD can only use soft and hard board. These three kinds of boards have the highest prices for hard and soft boards, while hard boards have the lowest prices.

Lens

Lens is second only to CMOS chip influencing the quality of the second element, the composition of the lens structure, composed of a few lenses, generally can be divided into plastic lenses (plastic) or glass (glass). Of course, the so-called plastic lens is not a pure plastic, but a resin lens, of course, the optical index of light transmittance is not comparable to the coated lens.

The camera lens structure usually used is:

1P, 2P, 1G1P, 1G2P, 2G2P, 2G3P, 4G, 5G, etc. The more lenses there are, the higher the cost, and the better the relative imaging effect; glass lenses are more expensive than resins. Therefore, a good quality camera should use multiple glass lenses! Most camera products on the market today generally use inexpensive plastic lenses or a glass-plastic lens (ie, 1P, 2P, 1G1P, 1G2P, etc.) to reduce the cost, which greatly affects the imaging quality.

The lens consists of a lens, a filter device, and a lens barrel. There are three lens parameters, namely, focal length f′, relative aperture D/f′, and field angle 2ω.

The lens focal length is an important index of the lens, which determines the ratio of objects and images. If the object is in infinity, the size of the image is determined by the formula y′=−f′·tanω (ω is the object field angle).

The relative aperture D/f' and the number of apertures F are the key optical indicators of the lens. Relative aperture, it means that can enter the lens to reach the film light energy, and thus determine the image plane illumination, which is defined as the ratio of the entrance pupil diameter D and the lens focal length f ', dark scenes and high-speed moving objects need large relative aperture objective lens, The large relative aperture objective lens can increase the image plane illumination. According to the relative aperture size, the photographic objective lens can be divided into weak light objective lens (D/f'1: 6.3 or less) Ordinary lens objective (D/f'1:5.6-1:3.5). (D/f'1:2.8-1:1.4) Super-light objective lens (D/f'1:1-1:0.8) In order to make the same lens use a different environment, usually the aperture diaphragm adopts continuously variable variable Light.

The reciprocal of the relative aperture is called the aperture coefficient, also called the F number, and the camera lens is marked with an F number. The national standard stipulates the arrangement of the number of light levels in terms of the size of the luminous flux.

0.7,1,1.4,2,2.8,4,5.6,8,11,16,22··· With the increase in the number of apertures, the light hole becomes smaller, the luminous flux decreases, and the aperture becomes one level worse. The luminous flux is twice the difference. For camera lenses, the lower the F number, the better the lens compatibility and the greater the range of use. The relative aperture also affects the depth of field in the image plane to achieve a clear depth of field - the depth of field. The larger the relative aperture, the greater the depth of field of the image, and the aperture size to control the depth of field during the photographic process.

The angle of view 2ω of the field of view 2ω photographic lens determines the range of the object space. The field of view of the photographic lens is determined by the diameter of the circular area with satisfactory imaging quality on the image plane, or the photosensitive surface of the photosensitive element used by the camera. The size is decided.

The basic types of photographic lens: 1, according to the lens focal length and angle of view is divided into: standard lens, short-focus lens, telephoto lens. 2, according to the lens focal length can be divided into: fixed-focus lens, zoom lens.

Holders and Filters

The role of the fixture is actually to fix the lens, and there will be a filter on the fixture.

Color filters are also known as "color separation filters." There are currently two color separation methods. One is the RGB primary color separation method, and the other is the CMYK complementary color separation method.

The primary color CCD has the advantages of sharp picture quality and true colors, but the disadvantage is noise. Generally, a digital camera with a primary color CCD is used, and most of the ISO sensitivity will not exceed 400. In contrast, the complementary color CCD has a Y yellow filter, which sacrifices the resolution of some images, but the ISO value can generally be set at 800 or more.

DSP (Digital Signal Processing Chip)

Its function is to optimize the digital image signal through a series of complex mathematical algorithm operations, and finally transmit the processed signal to the display.

DSP architecture framework: (1). ISP (image signal processor) (image signal processor); (2). JPEG encoder (JPEG image decoder).

The power of the ISP is the key to determining the smoothness of the image, and the performance of the JPEG encoder is also one of the key indicators. The JPEG encoder is divided into hardware JPEG compression and software RGB compression.

DSP control chip's role is: the data obtained by the sensor chip quickly and quickly spread to the baseband and refresh the sensor chip, so control the chip is good or bad, directly determine the picture quality (such as color saturation, clarity) and fluency.

The above-mentioned DSP is used in the CCD because the DSP chip of the CMOS sensor has been integrated into the CMOS. From the appearance point of view, they are a whole. The use of CCD sensor camera is divided into two separate parts of CCD and DSP.

Image Sensor

Among the main components of the camera, the most important one is the image sensor, because the importance of the photosensitive device to the imaging quality is self-evident.

The sensor converts the light transmitted from the lens into an electrical signal, which is then converted to a digital signal by the internal DA. Since each pixel of the sensor can only sense R light or B light or G light, each pixel is now stored in monochrome, and we call it RAW DATA data. To restore the RAW DATA of each pixel to three primary colors, a signal processor ISP is required to process it.

The image sensor is an element that acts as a light-sensitive recording, similar to film. There are two types of CMOS and CCD CCD, also known as charge transfer device, photodiodes arranged in a row called a one-dimensional linear sensor, photodiode line array called two-dimensional area image sensor.

The CCD consists of a photodiode photosensitive member, a ccd transfer member, and a charge amplifier device. When the light is irradiated, the photon excites the charge and the charge is accumulated. The gate voltage is applied between the photosensitive member and the transfer member, and the accumulated charge is under the effect of the gate voltage. The directional movement to the transfer member is started and the output is amplified. These output charge signals carry image information.

The development trend of image sensors is high-sensitivity, high-resolution, power saving, low-voltage work and other high-performance direction.

CMOS image sensors are made of metal oxide semiconductors. Each pixel can integrate multiple devices such as amplifiers, A/D converters, and so on.

The difference between the two photosensitive elements:

CCD imaging is of good quality, but it is more complicated to fabricate and consumes more energy. Although CMOS has poor imaging quality, it has low driving voltage and is easy to manufacture. CMOS can be integrated with other devices, and each pixel can achieve complete functionality. The CCD is arranged in thousands of pixels, and the charges excited by each pixel are brought together and transported to the amplifier and data processor. This imposes a lot of burden on subsequent processing, and a large amount of charge is collected, which also gives the channel a higher level. The technical requirements of the bottleneck, each pixel in the CMOS to complete the signal amplification and signal processing work alone, these features, resulting in greater CMOS noise. If CMOS overcomes the disadvantage of large noise and improves the imaging quality, CMOS will surpass CCD and become the first choice for image sensors.

Some manufacturers will mention "back-illuminated" "BSI" and other concepts in the publicity. Actually, BSI is the English abbreviation of back-illuminated CMOS. Back-illuminated CMOS is a kind of CMOS, which improves the traditional CMOS sensor. Sensitivity, in the night shot and high sense of the imaging effect is relatively better.

Cell phone camera imaging principle

The object light enters the system, passes through the lens, and reaches the image sensor. The photon hits the sensor to generate the movable charge. This is the internal photoelectric effect. The movable charge is assembled to form an electric signal. Since the processor cannot recognize the charge signal, the electric signal needs to be converted. For digital signals, for the image sensor CMOS system does not require an external analog-to-digital converter, and for the ccd image sensor system requires A / D converter, after the analog-digital conversion device, the charge signal is converted into digital signals, digital signals After the amplifier circuit enters the microprocessor, the digital signal is processed by the DSP digital signal processing chip and transmitted to the screen to form the same image as the object.

Some key factors that affect the performance of mobile camera

Pixels

Commonly referred to as "XXX million pixels" actually refers to the resolution of the camera. Its value is mainly determined by the number of pixels (ie, the minimum light sensing unit) in the camera sensor. For example, 5 million pixels means that there are 5 million pixels in the sensor. Pixels, and the number of pixels in the phone screen determines whether the screen is 720p or 1080p resolution.

Pixels determine photo quality?

It is usually thought that the higher the camera pixel, the clearer the picture taken, in fact. The camera's only pixel can determine the resolution of the picture it is taking. The higher the picture's resolution, the larger the picture's size, and the less clear the picture.

However, the current mainstream mobile phone screen is 1080p level (1920×1080 pixels), regardless of whether the 3208×2120 pixel photograph of the 13 million pixel camera or the 3200×2400 pixel photograph of the 8 million pixel camera exceeds the interpretation range of the 1080p screen. It will eventually be displayed with 1920×1080 pixels, so there is no difference in the sharpness seen by the naked eye.

Where are the advantages of high pixels?

Higher-pixel cameras take larger pictures. If we want to print the sample and print it using the standard 300 pixel/inch printing standard, the 4208×3120 pixel sample taken by the 13-megapixel camera can print 17 Inches, and the 3200 x 2400 pixel proofs of the 8 megapixel camera, the photos that print more than 13 inches begin to blur. It is clear that the 13-megapixel camera proofs can print larger sizes.

sensor

Since pixels are not the key factor in determining picture quality, who is it? The answer is a sensor.

There are two main types of camera sensors: CCD and CMOS. Although CCD sensors have good imaging quality, they are expensive and not suitable for mobile phones. CMOS sensors are most widely used in mobile phones because of their lower power consumption, price, and excellent image quality.

The CMOS sensor is divided into two types: back-illuminated and stacked-type. Both are the same door. The earliest technology was developed by Sony. The brand name of the Sony back-illuminated sensor is "Exmor R" and the stack sensor is "Exmor RS".

Relatively speaking, the larger the sensor size, the better the sensitometric performance. The more photons (graphics signals) are captured, the lower the signal-to-noise ratio is, and the better the imaging effect is naturally. However, the larger sensor will cause the volume and weight of the mobile phone. ,Increased costs.

The appearance of the back-illuminated sensor effectively solves this problem. Under the same size, it improves the sensor's photosensitivity by 100%, effectively improving the imaging quality under low light conditions.

In August 2012, Sony released a new stacked sensor (Exmor RS CMOS). It should be noted that it is not an evolutionary relationship with the back-illuminated sensor, but a side-by-side relationship. The main advantage of the stacked sensor is that the number of pixels remains unchanged. In the case of a variable sensor size, it can also be understood that when the number of pixels is the same as the number of pixels of the back-illuminated sensor, the size of the stacked sensor is smaller, thereby saving space and making the mobile phone thinner Lighter.

Lens

The lens is a device that images the subject on the sensor. It is equivalent to the “eye” of the camera. Usually it is composed of several lenses. When the light signal passes through, the lenses filter stray light (infrared rays, etc.), so the lens is The more numbers, the more realistic the imaging.

aperture

The aperture consists of several thin metal sheets in the lens. The amount of light entering the lens to reach the sensor can be controlled by changing the size of the aperture. The aperture value is usually represented by f/2.2, f/2.4, the smaller the number, the larger the aperture, and the inverse relationship between the two.

Its working principle is that the larger the aperture is opened, the more light that passes through the lens to reach the sensor, the brighter the image is, and the darker the image is. Therefore, in the night shoot or dark light environment, the imaging advantage of the large aperture is more obvious.

In addition to controlling the amount of light, the aperture also has the ability to control the depth of field. In life, we often see photos with strong bokeh effects, which not only highlights the focus of photography but also has a beautiful aesthetic sense. This is the so-called depth of field. The larger the aperture is, the smaller the depth of field is, and the blurring effect is more pronounced.