First, the camera (CAMERA), also known as PC cameras, computers and other eye it as a video input device that is widely used in terms of video conferencing, telemedicine and real-time monitoring in the past.
In recent years, with the development of Internet technology, the continuous improvement of network speed, coupled with mature technology and photographic imaging devices used extensively for the manufacture of the camera, which makes its price down to the level of ordinary people can afford. Ordinary people can be to each other through the network camera has audio and video, voice conversation and communication, in addition, it can also be used to present a variety of popular digital image, audio and video processing.
Second, the classification of the camera
Camera into digital cameras and analog cameras two categories.
Analog camera:
Analog camera analog video signal may be generated by video capture device into a digital signal, and then storing it in the computer. Analog camera video signal must be captured through a particular capture board converts analog signal into digital mode, and after compression may be converted to use the computer.
Digital Camera:
digital camera can capture an image directly, and then via the serial, parallel or USB interface to the computer inside. Now the camera on the computer market mainly basic digital camera, digital camera and turned around the use of new data transmission interface USB-based digital cameras currently on the market are mostly seen this product. In addition there is a complex product used in video capture card, but is not yet mainstream.
Due to the rapid spread of personal computers, the higher the overall cost of the analog camera and other reasons, USB interface transfer rate is much higher than the speed of the serial port, parallel port, so now the hot market mainly digital camera USB interface. The following mainly refers to the digital camera USB interface.
Third, the principle of the camera
The camera works approximately: generating an optical image of a scene through a lens (the LENS) projected onto the surface of the image sensor, then converted to electrical signals, after A / D (analog to digital) converter into a digital image signal, and then sent to the digital the signal processing chip (DSP) of the processing, and then processing to the computer through the USB interface, you can see the image through the display.
Note 1: an image sensor (SENSOR) is a semiconductor chip having a surface comprising hundreds of thousands to millions of photodiodes. When the photodiode is irradiated by light, charge is generated.
Note 2: a digital signal processing chip DSP (DIGITAL SIGNAL PROCESSING) Function: mainly, digital image signal processing parameters were optimized through a series of complex operations of mathematical algorithms, and processing the signals transmitted through the USB interface, such as a PC etc. .
DSP architecture framework:
ISP (image signal processor) (image signal processor) 2. JPEG encoder (JPEG image decoder)
USB device controller (USB device controller)
Fourth, the major structural components of the camera and
Works from the camera and can list the main structural components of the camera:
1, the lens (the LENS)
lens structure, composed of several pieces of lenses, a lens with a plastic (Plastic) or a glass lens (glass).
2, the image sensor (SENSOR) can be divided into two categories:
the CCD (CHARGE couple Device): Charge Coupled Device
CMOS (complementary metal oxide semiconductor): Complementary Metal Oxide Semiconductor
3, digital signal processing chip (DSP)
DSP manufacturers more, the market is more popular there :( Sonix) SONIX, VIMICRO (Vimicro), etc.
4, power supply
Camera requires two internal operating voltage: 3.3V and 2.5V, so a good camera internal power factor is to ensure a stable operation of the camera.
Fifth, the camera's number of technical indicators
1, the image resolution / resolution (Resolution): ● SXGA (1280 x1024), also known as 1.3 million pixels ● XGA (1024 x768), also known as 800 000 pixels
2, image formats (Image Format / Color space) RGB24, I420 is currently the two most commonly used image formats.
● RGB24: represents R, G, B three colors each 8bit, 256 may exhibit a maximum gradation, thereby reproducing 256 256 256 colors.
● I420: YUV one of the formats.
● Other formats: RGB565, RGB444, YUV4: 2: 2 and the like.
3, automatic white balance adjustment (AWB)
Definition: color temperature requirements in different environments, according to a white object, the screen is the image to be white. Spectral components represent color temperature, color of light. Low color temperature implies more than long wavelength components.
When the color temperature is changed, the ratio of the light sources (red, green, blue) of three primary colors vary, necessary to adjust the ratio of three primary colors to achieve color balance, which is the actual white balance adjustment.
4, the image compression
JPEG: (joint photographic expert group)
still image compression. A lossy compression of the image. The greater the compression, the image quality is also worse. When less precision is limited image storage space, this format can be selected. At present, most digital cameras use the JPEG format.
5, the color depth (number of bits of color)
reflected color performance of color recognition and imaging
is actually quantization precision A / D converter refers to the number of signals into levels. Common color digit (bit) representation. The higher the color depth, the more bright colors and moving images obtained.
6, the image noise refers to the noise image in the aggravation. The performance of a fixed color image is grainy.
7, the perspective of
the human eye is complementary imaging principle, it simply is the imaging range.
8, an output / input interface
serial interface (RS232 / 422): transfer rate is slow, a parallel interface (PP) is 115kbit / s: rate of up to 1Mbit / s
infrared interface (IrDA): is a rate of 115kbit / s, a typical laptop this interface has a
universal serial bus USB: plug and play interface standard, hot-swappable. USB1.1 rate of up to 12Mbit / s, USB2.0 up to 480Mbit / S
the IEEE1394 (Firewire) interface (also known as iLink): its transmission rate up to 100M ~ 400Mbit / s
Sixth, to further understanding of the camera
From the composition of the camera view to determine a camera quality from the hardware it is mainly:
1, the lens (the LENS)
consisting of a lens is a lens structure, composed of several pieces of lenses, generally plastic lens (Plastic) or a glass lens (Glass) . Typically the camera with a lens configured with: 1P, 2P, 1G1P, 1G2P , 2G2P, 4G and the like. The more lenses, the higher the cost; glass lens more expensive than plastic. Thus a good quality camera should be a glass lens, plastic lens relative to the imaging effect will be better. Most cameras now on the market in order to reduce costs, generally with plastic or semi-plastic half-lens glass lens (i.e.: 1P, 2P, 1G1P, 1G2P etc.). 2, the image sensor (SENSOR)
2, the image sensor is divided into two categories: CCD (charge couple device): a charge coupled device. CMOS (complementary metal oxide semiconductor): Complementary Metal Oxide Semiconductor
CCD advantage of high sensitivity, low noise, signal to noise ratio. But the complicated production process, high cost, high power consumption. CMOS has the advantage that high integration, low power (less than 1/3 CCD), and low cost. However, relatively large noise, low sensitivity, high requirements on the light source.
CCD imaging often permeability, sharpness is good in the same pixel, color reproduction, exposure may be substantially guaranteed accurate. Disk, digital cameras tend to the direction of development, it is also conceivable camera may later have the scanner function) and so is the future trend of development;
3, more user-friendly, easier to use, more of the real needs of practical applications is the customer. "Daily Precautions"
1, daily use camera, should note the following:
a, do not point the camera directly to the sun, so as not to damage the image sensing device camera.
B, to avoid contact with the camera and the material oil, steam, water vapor, dust, moisture and the like, to avoid direct contact with water.
c, do not use detergents or stimulating an organic solvent wipe camera.
d, twist, pull or cable, similar action might cause damage to the camera.
Under e, non-essential situation, do not arbitrarily open the camera, trying to touch the internal parts, so easy to damage the camera.
F, usually the camera should be stored in a clean, dry place.
1. photosensitive member
Currently on the market mainstream camera sensor used mainly both CCD and CMOS. Their role equivalent to the traditional camera film. High resolution CCD, lifelike color reproduction, has become megapixels level digital photographic equipment protagonist; compared with CCD, CMOS has a low cost and energy saving, and therefore almost all the low-end camera using a CMOS sensor .
Deficiencies CMOS camera is high requirements for light generated coarser than the effect of the image of the CCD. Some readers may notice that currently the CMOS sensor some high-end SLR digital camera used, but both are technically quite different. Moreover, for the camera, the effect is often not the most important, low-cost CMOS camera shooting out the effect can also be acceptable.
2. The pixel values and resolution
And resolution pixel value herein refers to the resolution of the optical resolution is an important indicator of two cameras. Pixel value refers to the number of separate image pixel, determined by a CCD or CMOS. The larger the value of the pixel, the stronger its image resolution capability.
The current mainstream camera pixel value of the product is generally 300,000, 350,000 and 380,000, and 50 million or 1.3 million, though relatively rare, the price is high. Resolution is the ability to identify the camera image, which (except for interpolation) the maximum pixel value determined by the camera.
Such as the current level of 30-megapixel camera can provide the maximum resolution of 640 × 480, but a lot of chat software (such as MSN) supported by default resolution is only 320 × 240, it is equivalent to 100,000 pixels. I want to point out that, in theory, the pixel value is greater only that image is more delicate and clear, but the pixel value is determined not only image quality.
In addition, the time of purchase but also ask pixel values are clearly the nominal or real pixel interpolation income, or whether the effect because both come from the cost comparison, has a world of difference. What is the pixel interpolated it? Interpolated pixel is calculated using a mathematical formula "lost" on the basis of surrounding pixels on the pixel.
There are many on the market only sell tens of dollars of camera is to deceive consumers in this way, although they are also nominal 30 million pixels, but the truth is only 100,000 pixels. Of course, ask the merchant is not very reliable Moreover, sometimes they were also "victims" (only the manufacturers know). In fact, imaging 100,000 pixels and 300,000 pixels are significantly different from the clarity and color saturation on the screen, the naked eye can tell the difference alone.
3. The maximum frame rate
In addition to pixel values and resolution, frame rate when shooting is also an important factor determining the quality of the picture, you can interpret it how many pictures the camera samples per second. Thus it is easy to understand: the higher the sampling rate, of course, the smoother image. In practice, only a screen refresh in more than 24 frames / second, the human eye will not notice significant pause.
Limited cost, the current maximum frame rate of most mainstream camera at 30 frames / second, low-end products only 15 frames / sec or less. Better performance of a camera, which should reach the maximum frame rate 30 frames / sec (352 × 288), i.e., using the standard VGA format (640 × 480) imaging, also have 15 frames / second refresh rate.
4. The focal length of the lens and
The camera lens position is equivalent to the human eye, bright and clear images whether shooting often depends on the quality of the lens. Costs shot up a large proportion of the entire camera. Accordingly, the same function the same two camera pixels, using different lenses, cost may vary greatly. Such as those using cheap plastic lens products relatively cheaper.
And the lens should be better recognized with glass, or glass fibers produced by the multi-piece lens elements. Whether the coating is also a factor in evaluating the quality of the lens, how to distinguish the lens has no coating? Simple, viewed from the side of the lens coated with purple or blue-green (depending on the color of refraction of the plated film is also different) luster while not coating does not have these shiny.
Some users to buy back after the camera images found very vague, and in the time trial, where the business is good, why is this so? Are generally not adjusted the focus caused. And shoot cameras, the camera uses a super-focal length, depth of field, macro big but when manual focus. So, sometimes you need to manually adjust the focal length of the camera to get the clearest picture.
Tip: Due to the relatively large depth of field of the lens, can people call for a clear image of the future focus for ultra-distance focal length. Application of ultra-focus is to obtain maximum depth of field or the most efficient method of controlling image clarity range. Shoot cameras generally is the use of ultra-focus, the use of short-focus lens scene after a certain distance can be relatively clear imaging characteristics, eliminating the need for focus.
The processing chip
A very important factor is the impact of chip imaging results. Such as poor quality of some products using the chip, it will cause the camera can not be used in case of poor light. A camera in the end what kind of processing chip, unless the open inspection, or else we do not know, can only be judged by tangible results. What is CMOS camera?
The main difference between CCD and CMOS fabricated on a CCD are integrated on a semiconductor single crystal material, and CMOS are integrated on a semiconductor material is referred to as metal oxide, is not essentially different principle. CCD only a few manufacturers such as Sony, Panasonic and other master this technology. And CCD manufacturing process more complex, a CCD camera will be relatively expensive price. In fact through technological innovation, the current gap between the CCD and CMOS practical effect has been reduced a lot. And CMOS manufacturing cost and power consumption should be lower than the number of CCD, CMOS sensor so many camera manufacturers adopted. Imaging: CCD imaging permeability, sharpness is good in the same pixel, color reproduction, exposure may be substantially guaranteed accurate. The permeability of CMOS products are often general, color reproduction of the kind of weak, exposure is also not very good, because of their physical characteristics, image quality CMOS and CCD or a certain distance. However, due to low prices and a high degree of integration, so the field is still in the camera has been widely used.