The current mainstream products of face access control are integrated face access control products with screens, due to the many manufacturers, a variety of product functional components, product performance indicators vary greatly, often leading to the user's choice of face access control products are more difficult, but also more difficult to face access control through objective indicators of equipment reviews. This section of the integrated face access control of the main product module components and mainstream technical solutions for comparative analysis, for product manufacturers to design and develop face access control products and users to choose face access control products to provide technical specifications for reference. The following description of integrated access control products directly collectively referred to as access control products.
Integrated face access control products hardware is mainly divided into the upper and lower part, this article mainly describes the principle of the camera, imaging, components, etc.
All-in-one access control product components
Integrated biometric face recognition time clock face access control products are usually composed of camera modules, human body sensor modules, complementary light modules, proximity cards or keypads, main control boards, displays, linkage output modules, etc.. Some products replace the keyboard by touch screen, or directly omit the proximity card module, are related to product design and positioning.
Camera imaging module
Camera imaging module is the key component of integrated face access control products, which is related to the acquisition capacity and application range of face recognition imaging. The main technical parameters affecting the camera imaging module are the interface type, light-sensitive range, the number of lenses and other key indicators.
1. Basic principle
A typical camera module consists of lens, sensor, ISP module, video coding module and so on. Depending on the type of interface ISP or video encoding module may also be integrated in the main control board.
The main parameters are focal length, aperture and depth of field. About the focal length, aperture and depth of field involves more optical content, here will not expand.
determines the low illumination and wide dynamic imaging capabilities of the lens, which determines whether the access control device in outdoor applications, indoor applications and other different ranges of application.
Digital signal processing ISP.
affects a variety of functions such as image white balance, distortion correction, and focus control.
Related to the type of camera module, USB and MIPI cameras usually do not perform video compression coding, network cameras involve video compression coding issues.
2. Camera modules into image devices
Biometrics face recognition access control as a whole is a highly integrated product, camera modules are often derived from computer cameras, cell phone cameras or security surveillance cameras several existing products. According to the different sources of camera imaging chips, can be divided into the following types.
The first type: the computer camera-based indoor imaging camera module
Laptop computers, desktop computers supporting desktop USB cameras are usually used in desktop, reception and other indoor application scenarios, the distance between the person being photographed and the device is usually within 1 meter, indoor light stability does not exist in large changes, this computer camera-based indoor imaging camera modules in face access control are used in large numbers.
Typical indicators for desktop computer-based indoor imaging camera modules are
Face detection distance: within 1 meter.
face clarity: mainly D1, 720P or 1080P.
Wide dynamic light adaptability: requires uniform light in the face, does not have the ability to adapt to wide dynamic light.
Low-illumination imaging capability: suitable imaging illumination is 100-3000 Lux, does not have low-illumination imaging capability.
Scope of application: indoor access control or face detection and recognition under good environment.
The second category: cell phone camera-based wide dynamic imaging module
With the development of smart phones, the imaging capability of a large number of smart phone camera modules has been greatly improved, and the mainstream cell phone cameras have a qualitative change in imaging quality compared to desktop USB cameras. These cameras are usually based on MIPI interface cameras, and a few still exist in the form of USB interface.
Typical indicators of cell phone camera modules mainly with a certain degree of wide dynamic module are
Face detection distance: within 0.5 m - 2 m.
Face clarity: mainly 720P or 1080P.
Wide dynamic light adaptation capability: with a wide dynamic imaging capability of 60db-80db.
Low-illumination imaging capability: capable of low-light imaging, suitable imaging illumination of 30-3000 Lux, primary low-illumination imaging.
Scope of application: indoor or floor, unit door imaging with fill light environment.
The third category: the security surveillance camera chip-based low-light wide dynamic imaging module
Security cameras are usually outdoor-oriented, and to adapt to strong light, low light at night and other scenarios, security cameras have a professional-grade imaging chip has a better low-light wide dynamic imaging capabilities. Typical indicators of such modules are.
Face detection distance: 0.5 m - 5 m.
face clarity: mainly 720P or 1080P.
Wide dynamic light adaptation capability: with 80db-100db of wide dynamic imaging capability.
Low-illumination imaging capability: capable of shimmering or low-light imaging, with a suitable imaging illumination of 0.1-5000 Lux.
Scope of application: outdoor face recognition in parks and communities, face recognition applications at outdoor entrances and exits of buildings.
3. Camera interface type
The interface type of camera module and the volume of the camera, the application range has a greater relationship. The following interface types are mainly available
Most of the common computer cameras are usually USB cameras, which are the most widely used camera modules and have high market share and good compatibility.
Universal Serial Bus (English: Universal Serial Bus, abbreviation: USB) is a serial bus standard connecting computer systems and external devices, but also an input and output interface specifications, is widely used in personal computers and mobile devices and other information and communication products, and extended to photographic equipment, digital TV (set-top box), game consoles and other related fields. The latest generation is USB 3.1, transmission speed of 10Gbit / s, three-stage voltage 5V/12V/20V, the maximum power supply 100W ,the new Type C plug type is no longer divided into positive and negative.
USB is a commonly used pc interface, he has only four lines, two power two signals, so the signal is serial transmission, usb interface is also known as the serial port.
The general arrangement is: red, white, green and black from left to right.
Red-USB power: marked with -VCC, Power, 5V, 5VSB words
White - USB data line: (negative) -DATA-, USBD-, PD-, USBDT-
Green - USB data cable: (positive) -DATA+, USBD+, PD+, USBDT+
Black - Ground: GND, Ground
USB 1.0 appeared in 1996 with a speed of only 1.5Mb/s (bits per second); it was upgraded to USB 1.1 in 1998, and the speed was greatly increased to 12Mb/s. USB 1.1 is the more common USB specification, with a transfer rate of 12Mbps for the high-speed mode and 1.5Mbps for the low-speed mode (b is the meaning of Bit). Most MP3s are of this type of interface type.
The USB 2.0 specification is an evolution of the USB 1.1 specification. USB 2.0 can be used to drive USB 1.1 devices with USB 2.0 drivers, and accessories like USB cables, plugs, etc. can be used directly.
USB 3.0 by Intel, Microsoft, HP, Texas Instruments, NEC, ST-NXP and other industry giants formed the USB 3.0Promoter Group has been officially completed and publicly released. USB 3.0 physical layer using 8b/10b encoding method, theoretical speed is 4Gb / s, can be widely used in PC peripherals and consumer electronics.
The mainstream smartphone camera is MIPI interface camera module. MIPI camera is commonly used in cell phones and tablets, supporting more than 5 megapixel HD resolution.
MIPI (Mobile Industry Processor Interface) is the abbreviation of Mobile Industry Processor Interface, a mobile device interface specification developed by the MIPI Alliance, an open membership organization. The MIPI Consortium aims to promote the standardization of mobile application processor interfaces. MIPI is a differential serial interface transmission, fast and anti-interference. Mainstream cell phone modules with MIPI transmission, transmission using four pairs of differential signals to transmit image data and a pair of differential clock signals.
MIPI-CSI interface usually collects data from COMS Sensor, Video Encoder and other video output devices.
Camera Serial Interface (CSI) is an interface specification developed by MIPI (Mobile Industry Processor Interface Consortium), which belongs to the same family as DSI. It is divided into the following protocols.
CSI-1: CSI-1 is the original standard MIPI interface for cameras. It serves as an architecture to define the interface between the camera and the host processor. Its successors are MIPI CSI-2 and MIPI CSI-3, two standards that are still evolving.
CSI-2: The MIPI CSI-2 v1.0 specification was released in 2005. It uses either D-PHY or C-PHY (both standards set by the MIPI Consortium) as a physical layer option. The protocol is divided into the following layers.
Physical layer (C-PHY/D-PHY)
Lane merging layer.
Low-level protocol layer.
Pixel-to-Byte conversion layer
CSI-3: MIPI CSI-3 is a high-speed bi-directional protocol primarily used for image and video transmission between cameras and hosts in multi-layer peer-to-peer UniPro-based networks of M-PHY devices. It was originally released in 2012 and re-released in 2014 in version 1.1.
For EMI reasons, system designers can choose two different clock rates (a and b) in each M-PHY speed class. m-PHY speed clock frequency bit rate gear 1G1A 1.25Gbits/sG1B 1.49Gbits/s gear 2G2A 2.5Gbits/sG2B 2.9Gbits/s gear 3G3A 5Gbits/s, G3B 5.8Gbits/s.
C.RJ45 network interface
Most of the current mainstream security surveillance cameras for network interface cameras.
Network camera module usually refers to the use of the SOC program represented by Heisi, the video capture, video encoding and compression, video transmission and other debugging integrated into one camera module. Network camera module is very widely used in the security field.
D. Other interfaces
Camera modules also involve LVDS, parallel signals, analog signal transmission and other interface methods, which are less used in face access control.
4. The number of imaging lenses
Refers to a single camera for video capture and face detection. Monocular camera is the largest number of camera module type at present.
B.Visible and near infrared binocular type
Refers to the use of dual sensors for video acquisition, one of the sensors is visible sensor for face information acquisition and comparison imaging; the other sensor is NIR sensor for face live detection and other functions.
C. Dual visible light binocular type
Binocular imaging (Stereo System): using dual cameras to photograph objects, and then calculate the object distance through the triangle principle. Refers to the use of two visible light sensors for camera imaging, two sensors and lenses are used visible light, through binocular three-dimensional measurement and other methods for live detection of the face. Binocular distance imaging because of low efficiency, difficult algorithms, poor accuracy, and susceptible to interference by environmental factors.
It consists of two monocular cameras (the distance between the two cameras is called "baseline" is known), through this baseline to estimate the spatial location of each pixel to measure the distance between the object and us, to overcome the shortcomings of monocular cameras can not know the distance. The depth range measured by the binocular camera is related to the baseline, and the larger the baseline distance, the farther it can be measured.
Can be used indoors as well as outdoors.
configuration and calibration is more complex, its depth and accuracy is limited by the baseline or resolution of the binocular, and the calculation of parallax is very consuming computer resources, under the existing conditions, the amount of calculation is one of the main problems of binocular.
D. Binocular structured light type
Structured Light (Structured Light): Structured Light projects specific light information onto the surface of the object after it is captured by the camera. According to the change of light signal caused by the object to calculate information such as the position and depth of the object, and then recover the whole three-dimensional space.
Summary: By analyzing the imaging devices, interface types, and number of lenses of camera modules, the current mainstream cameras can be divided into three categories.
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