Camera Module: The Ultimate Guide for Beginners
If you’ve purchased a phone, computer, or tablet, you’ve likely heard of the camera module. It is the main unit for image and video input. camera module is not just a small circle on the back of your phone. It is a module that is a combination of highly sophisticated components.
Today, we’re going to find out what camera module is all about.
What is Camera Module
Camera Module, also known as Camera Compact Module, abbreviated as CCM, contains four major components: lens, sensor, FPC, and DSP. The important parts to decide a camera is good or bad are: lens, DSP, and sensor.The key technologies of CCM are: optical design technology, aspherical mirror production technology, optical coating technology.
Working principle: the object through the lens (lens) gathered light, through CMOS or CCD integrated circuit, the light signal into electrical signals, and then through the internal image processor (ISP) into a digital image signal output to the digital signal processor (DSP) processing, into a standard GRB, YUV and other formats image signal.
2. Camera Module Components
2.1 Lens (lens)
Lens is a device that can receive light signals and converge light signals in the sensor CMOS/CCD. lens determines the light harvesting rate of the sensor, its overall effect relative to a convex lens. Optical lens structure is: lens barrel (Barrel), lens group (P / G), lens protection layer (gasket), filter, lens holder (Holder).
Camera module lens is divided into plastic lens (PLASTIC) and glass lens (GLASS), the general camera lens consists of several lenses, usually the lens for camera module is: 1P, 2P, 3P, 1G1P, 1G2P, 2G2P, 4G, etc.. The more the number of lenses, the higher the cost; in general, the glass lens will have better imaging effect compared with the plastic lens. However, the glass lens will be more expensive than the plastic lens.
2.1.1 Lens main indicators
A, eliminate as much Flare
B, picture quality clarity
C, CRA (Chief Ray Angle main light angle) to match, reduce shading (Lens cra < Sensor CRA, the difference is best within 2 degrees)
D. Aperture as large as possible
E. Distortion as slight as possible, etc.
2.1.2 Lens and main parameters
(1) Focal length: The length of the lens focal length determines the imaging size of the camera module, the size of the field of view, the size of the depth of field and the strength of the perspective of the picture. Generally speaking, for a single lens is the distance from the center of the lens to the focal point, while the camera lens is a combination of multiple lenses, it is much more complicated. Here the focal length refers to the distance between the center point of the lens to the light-sensitive components (CCD) formed on the clear image.
(2) field of view: we often use the horizontal field of view to reflect the range of the picture. The larger the focal length f, the smaller the field of view angle, the smaller the range of images formed on the sensor; conversely, the smaller the focal length f, the larger the field of view angle, the larger the range of images formed on the sensor.
(3) F value (caliber ratio): F value refers to the brightness of the lens (that is, the amount of light transmission of the lens). f = lens focal length / aperture diameter. f value of the same, long focal length lens caliber than the short focal length lens caliber large.
(4) Aperture: Aperture is located inside the lens, can be adjusted optomechanical appendix hole, can be used to control the amount of light through the lens. Variable aperture (Iris diaphragm). A mechanical device inside the lens used to control the size of the diaphragm aperture. Or refers to the device used to open or close the lens diaphragm hole, thereby adjusting the f-stop of the lens.
(5) depth of field: when an object in focus clear, from a certain distance in front of the object to a certain distance behind it, all the scenery is also equivalent to be clear. The distance from the front to the back of the focal point is called the depth of field.
2.2 VCM for camera module (Voice Coil Motor)
Full name Voice Coil Montor, electronics inside the voice coil motor, is a kind of motor. Because the principle is similar to the speaker, so called voice coil motor, with high frequency response, high precision characteristics. Its main principle is in a permanent magnetic field, by changing the size of the DC current in the motor coil to control the stretching position of the spring, so as to drive the up and down movement. Camera compact module widely use VCM to realize the autofocus function, and the position of the lens can be adjusted by VCM to present clear images.
2.2.1 VCM performance index
The performance of VCM mainly depends on the ratio of current and travel distance. Starting from the starting current, the current rise should be proportional to the travel distance that can be driven, the smaller the rise current needed, the higher the accuracy, and also look at the maximum power consumption, the maximum power, and the size of the size.
2.2.2 VCM Classification
From the structure can be roughly divided into three categories: (1) shrapnel type structure; (2) ball type structure; (3) friction type structure.
From the function of the roughly divided into five categories: (1) Open loop open motor; (2) Close loop closed loop motor; (3) Alternate in the motor; (4) OIS optical anti-shake motor (divided into translation type, shift type, memory metal type, etc.); (5) OIS + Close loop six-axis motor.
2.2.3 AF principle
After entering the autofocus mode, Driver from 0 to the maximum value, so that the lens from the original location to the maximum displacement, at this time the sensor imaging surface automatically take pictures and saved to the DSP, DSP through these pictures, calculate the MTF (Modulation transfer function) value of each pair of pictures, so as to find the maximum value in this MTF curve, and through the algorithm, to get this point corresponds to the size of the current, and once again instruct Driver to provide this current to the voice coil, and make the lens stable in this imaging surface, so as to achieve the auto-zoom.
2.2.4 Zooming and Focusing
A: achieve optical zoom using zoom motor (ZOOM)
By moving the lens inside the lens to change the position of the focal point, change the length of the lens focal length, and change the size of the lens perspective, so as to achieve the impact of the magnification and reduction.
B: Achieving autofocus using focus motor (AF)
The position of the entire lens (rather than the lens inside the lens) is moved over a slight distance to control the length of the lens focal length, and to achieve a clear image. This is a common method used in cell phones.
The difference between optical focus and optical zoom:
Optical zoom is to change the position of the focal point by moving the relative position of the lenses inside the lens, changing the length of the focal length of the lens and changing the size of the perspective of the lens, so as to achieve the magnification and reduction of the image.
Optical focusing is actually adjusting the position of the entire lens (rather than the position of the lens inside the lens) to control the image distance, so that the image is the clearest.
2.3 IR CUT (infrared Cut Filter)
There are various wavelengths of light in nature, the human eye to identify the wavelength range of light between 320nm-760nm, more than 320nm-760nm light the human eye can not see; and the camera imaging components CCD or CMOS can see most of the wavelengths of light. Due to the involvement of a variety of light, the color restored by the camera and the naked eye in the color deviation. Such as green plants become gray, red pictures become light red, black becomes purple, etc.. At night due to the filtering effect of the bimodal filter, so that the CCD can not take full advantage of all the light, not to produce snow noise phenomenon and its low-light performance is difficult to be satisfactory. To solve this problem, the use of IR-CUT double filter.
IR-CUT dual filter is a set of filters built into the camera lens set, when the lens outside the infrared sensor point to detect changes in the intensity of light, the built-in IR-CUT automatic switching filter can be based on the strength of external light and then automatically switch, so that the image to achieve the best results. In other words, the dual filters can automatically switch filters in daytime or nighttime, so that the best imaging effect can be obtained whether in daytime or nighttime.
2.3.1 IR-CUT Composition and Principle
The IR CUT dual filter switcher consists of an IR cut-off low-pass filter (an IR cut-off or absorption filter), a full-spectrum optical glass (a full-transmission spectral filter), a power mechanism (which can be electromagnetic, motor or other power source) and a housing, which is switched and positioned by a circuit control board. When the light is sufficient during the day, the circuit control board drives the switcher to switch and position to the infrared cut-off filter work, CCD or CMOS camera module restore the true color; when the visible light is insufficient at night, the infrared cut-off filter automatically move away, the full-spectrum optical glass begins to work, at this time, it can sense the infrared light of the infrared lamp, so that the CCD or CMOS make full use of all the light, thus greatly improving the IR camera’s night vision performance, the whole picture is also clear and natural.
2.3.2 IR-CUT indicators
a, the infrared cut-off degree of the filter, light transmission, and light shaping effect, etc.
b, power drive part
c, control circuit
4, filter: generally use the method of coating (IR Coating) or blue glass to filter out infrared light.
2.4 Image Sensor
Image sensor is a semiconductor chip, its surface has millions to tens of millions of photodiodes, photodiodes
by the light will generate an electric charge, the light will be converted into electrical signals. Its function is similar to the human eye, so the performance of sensor will directly affect the
performance of camera.
2.4.1 Sensor structure
Sensing element: CCD, CMOS (PPS and APS)
What is CCD
CCD sensor, the full name of the English: Charge-coupled Device, the full name of the Chinese: charge-coupled elements. A CCD is a semiconductor device that converts optical images into digital signals. CCD image sensor is composed of many photosensitive material, each unit is called a pixel. The more pixels a CCD contains, the higher the resolution of the image it provides. a CCD works like film, but it converts image pixels into digital signals. a CCD has many neatly arranged capacitors that sense light and convert the image into a digital signal. Controlled by external circuitry, each small capacitor is able to transfer its charge to its neighboring capacitors.
What is CMOS
CMOS (Complementary Metal-Oxide-Semiconductor) is a semiconductor that can be subdivided into Passive Pixel Sensor CMOS and Active Pixel Sensor CMOS. It is an important chip in a computer system that holds the most basic data for system guidance.CMOS Image Sensor consists of Micro Lens, Color filiter, Photodiode, and Shift register.
Different processes: front-illuminated FSI, back-illuminated BSI, stacked type
There are many light-sensitive units on the sensor, which convert light into electrical charge to form an electronic image corresponding to the scene. And in the sensor, each light-sensitive unit corresponds to a pixel (Pixels), the more pixels, means it can sense more details of the object, and thus the image is clearer, the higher the pixel, means the clearer the imaging effect. The product of the camera resolution is the pixel value, for example: 1280 × 960 = 1228800
2. Target surface size
The size of the light-sensitive part of the image sensor, generally expressed in inches. As with the TV, usually this data refers to the diagonal length of the image sensor, such as the common 1/3 inch, the larger the target surface, meaning the better the amount of light, and the smaller the target surface is easier to obtain a greater depth of field.
That is, through the CCD or CMOS and related electronic circuits to sense the intensity of incident light. The higher the sensitivity, the stronger the sensitivity of the light surface, the higher the shutter speed, which is especially important when shooting sports vehicles, night surveillance.
4. Electronic shutter
Is a term proposed in comparison to the mechanical shutter function of the camera. Its control of the image sensor light sensitivity time, because the image sensor light sensitivity value is the accumulation of signal charge, the longer the light sensitivity, the longer the accumulation of signal charge time, the output signal current amplitude is also greater. The faster the electronic shutter, the lower the sensitivity, suitable for shooting in bright light.
5. Frame rate
Both refer to the number of pictures recorded or played back per unit of time. According to the human visual system, when the playback speed of the picture is greater than 15 frames/s (i.e. 15 frames), the human eye will not be able to see the jump of the picture; when it reaches 24 frames/s – 30 frames/s (i.e. 24 to 30 frames), it will be basically imperceptible. flicker is no longer noticeable.
The frames per second (fps) or frame rate indicates the number of updates per second that the graphics sensor can make while processing the field. A high frame rate results in a smoother and more realistic visual experience.
6. Signal to Noise Ratio
Is the ratio of the signal voltage to the noise voltage, the signal-to-noise ratio in dB to express. The general camera gives the signal-to-noise ratio value are AGC (Automatic Gain Control) off the value, because when the AGC is on, it will boost the small signal, making the noise level also increased accordingly.
The typical value of the signal-to-noise ratio is 45 – 55dB, if 50dB, the image has a small amount of noise, but the image quality is good; if 60dB, the image quality is excellent, no noise, the greater the signal-to-noise ratio indicates that the better the control of noise. This parameter relates to the number of noise in the image, the higher the signal-to-noise ratio, the cleaner the picture gives the impression, the less noise in the night vision picture in the form of dots.
Digital Signal Processor (DSP) is a microprocessor especially suitable for digital signal processing operations, and its main application is the real-time and rapid implementation of various digital signal processing algorithms.
Function: The main purpose is to optimize the digital image signal parameters through a series of complex mathematical algorithms, and to transmit the processed signal to cell phones, computers and other devices via USB and other interfaces.
2.5.1 DSP and ISP difference
ISP also know as Image Signal Processor, Mainly used to process the output signal of the front-end image sensor to match the image sensors of different manufacturers.
DSP also called digital signal processor, it is a microprocessor that is particularly suitable for digital signal processing operations. Its main application is to quickly implement various digital signal processing algorithms in real time..
ISP is a chip used to process the output data of the image sensor, for example: AEC (automatic exposure control), AGC (automatic gain control), AWB (automatic white balance), color correction, lens shading, gamma correction, removal of dead pixels, Processing of functions such as automatic black level and automatic white level.
DSP is another chip with more functions, such as processing of photos and playback (JPEG encoding and decoding), video and playback (video encoding and decoding), H.264 encoding and decoding, in short, it is processing digital signals.
3. classification and related concepts
Camera Module Classification and related concepts
3.1 Classification By interface
3.1.1 USB Interface camera module
UVC, or USB Video Class, is a set of standards customized by the USB-IF. Almost all USB camera modules with USB interface that follow the UVC standard can be used directly under Windows Linux and other systems to achieve a driverless effect.Of course, it doesn’t mean that you don’t really need a driver, but as long as a USB camera module follows the UVC standard, it can be driven by a common set of drivers in Window and Linux systems, and you don’t need to install other drivers. For example, there is a common set of drivers for UVC devices in the Linux kernel: drivers/media/usb/uvc, and almost all UVC cameras can be used directly with this set of drivers turned on.
3.1.2 MIPI interface camera module
MIPI (Mobile Industry Processor Interface) is the abbreviation for Mobile Industry Processor Interface, an open standard for mobile application processors initiated by the MIPI consortium.
The MIPI organization works to standardize interfaces within mobile communication devices to reduce compatibility issues and simplify design. Examples include the camera interface CSI, the display interface DSI, the RF interface DigRF, the microphone/speaker interface SLIMbus, etc.
3.1.3 DVP interface camera module
DVP is parallel port transmission, slower, low bandwidth transmission, use requires PCLK\sensor output clock, MCLK (XCLK)\ external clock input, VSYNC\ field synchronization, HSYNC\ line synchronization, D[0:11]\ parallel port data – can be 8/10/12bit data bit size.
3.1.4 LVDS interface camera module
LVDS (Low Voltage Differential Signaling) that is, low-voltage differential signal transmission
Network port: IPC webcam
3.1.5 SDI interface camera module
professional video interface, using coaxial cable, take the digital signal, now there are 18GHz bandwidth products, can meet the 8K video transmission.
RGB interface: analog video interface, using coaxial cable, go analog signal, 720×576 SD signal below.
EDP interface: relatively new specification, will be widely used in the notebook industry to replace LVDS, support ultra-high resolution, support 1080P or more
3.2 Classification by lens
Wide angle lens
3.3 By imaging points
Color camera module
Black and white camera module
Infrared camera camera module
3.4 BY the Image Sensor Type
CCD camera module
CMOS camera module
3.5 By whether the focal length is adjustable
Fixed focus camera
3.6 By sensor package
Your choice of camera modules will depend on the application you are working on – they must be compatible with the functionality you expect. For example, if you want a high resolution and specified len angle customization is required.
Therefore, check this guide before buying a camera module if you have everything so as not to waste time buying the wrong plate camera.
Have a nice day.