Introduction to Camera

1. Camera (CAMERA), also known as computer camera, computer eye, etc., as a video input device, has been widely used in video conferencing, telemedicine and real-time monitoring in the past.
In recent years, with the development of Internet technology and the continuous improvement of network speed, coupled with the maturity of photosensitive imaging device technology and a large number of them used in the manufacture of cameras, its price has dropped to a level that ordinary people can afford. Ordinary people can also talk and communicate with each other with audio, video and voice on the network through the camera. In addition, people can also use it for various popular digital image and audio and video processing.

2. Classification of cameras
Cameras are divided into two categories: digital cameras and analog cameras.

Analog camera:

The analog camera can convert the analog video signal generated by the video capture device into a digital signal, which is then stored in the computer. The video signal captured by the analog camera must be converted into a digital mode by a specific video capture card and compressed before it can be converted to a computer for use.

Digital camera:
Digital cameras can capture images directly, and then transmit them to a computer through a serial, parallel or USB interface. At present, the cameras on the computer market are basically digital cameras, and the digital cameras are mainly USB digital cameras using a new data transmission interface. Most of the products currently available on the market are such products. In addition to this, there is a product that works with video capture cards, but it is not mainstream yet.

Due to the rapid popularization of personal computers and the high overall cost of analog cameras, the transmission speed of the USB interface is much higher than the speed of the serial port and parallel port. Therefore, the current market hotspot is mainly the digital camera with the USB interface. The following mainly refers to the digital camera with USB interface.3. The working principle of the camera
The working principle of the camera is roughly as follows: the optical image generated by the scene through the lens (LENS) is projected onto the surface of the image sensor, and then converted into an electrical signal, which is converted into a digital image signal after A/D (analog-to-digital conversion) conversion, and then sent to the digital image signal. It is processed in the signal processing chip (DSP), and then transmitted to the computer for processing through the USB interface, and the image can be seen through the display.

Note 1: An image sensor (SENSOR) is a semiconductor chip containing hundreds of thousands to millions of photodiodes on its surface. When a photodiode is illuminated by light, an electric charge is generated.

Note 2: Digital signal processing chip DSP (DIGITAL SIGNAL PROCESSING) function: mainly through a series of complex mathematical algorithm operations, optimize the digital image signal parameters, and transmit the processed signals to PC and other equipment through USB and other interfaces .

DSP structure framework:

ISP (image signal processor) 2. JPEG encoder (JPEG image decoder)

USB device controller

Fourth, the main structure and components of the camera
From the working principle of the camera, the main structure and components of the camera can be listed:
1. Lens (LENS)
The lens structure consists of several lenses, including plastic lenses or glass lenses.

2. Image sensor (SENSOR) can be divided into two categories:
CCD (charge couple device): charge coupled device
CMOS (complementary metal oxide semiconductor): complementary metal oxide semiconductor

3. Digital Signal Processing Chip (DSP)
There are many DSP manufacturers, and the more popular ones on the market are: (Songhan) SONIX, VIMICRO (Zhongxingwei), etc.

4. Power

The camera needs two working voltages: 3.3V and 2.5V, so a good internal power supply of the camera is also a factor to ensure the stable operation of the camera.

Five, some technical indicators of the camera
1. Image resolution (Resolution): SXGA (1280 x1024), also known as 1.3 million pixels, XGA (1024 x768), also known as 800,000 pixels

2. Image format (Image Format/ Color space) RGB24, I420 are the two most commonly used image formats.

●RGB24: Indicates 8 bits for each of R, G, and B colors, and can express up to 256 shades, so that 256,256,256 colors can be reproduced.

●I420: One of the YUV formats.

●Other formats are: RGB565, RGB444, YUV4:2:2, etc.

3. Automatic white balance adjustment (AWB)

Definition: It is required that under different color temperature environments, the image on the screen should also be white when a white object is illuminated. Color temperature represents the spectral components, the color of light. A low color temperature means that there are many long-wavelength light components.
When the color temperature changes, the proportion of the three primary colors (red, green, and blue) in the light source will change, and the proportion of the three primary colors needs to be adjusted to achieve color balance, which is the reality of white balance adjustment.

4. Image compression method
JPEG: (joint photographic expert group)
Still image compression method. A method of compressing lossy images. The higher the compression ratio, the worse the image quality. This format can be selected when image accuracy is not required and storage space is limited. Most digital cameras today use the JPEG format.

5. Color depth (color bits)
Reflects the ability to recognize color and the ability to express color in imaging
In fact, it is the quantization accuracy of the A/D converter, which refers to how many levels the signal is divided into. Commonly used color bits (bit) representation. The higher the color depth, the more vivid the color of the image obtained.

6. Image noise refers to the clutter in the image. Appears as a fixed color noise in the image.

7. Perspective
Imaging with the human eye is the principle of phase formation, which is simply the imaging range.

8. Output/input interface
Serial interface (RS232/422): The transmission rate is slow, 115kbit/s Parallel interface (PP): The rate can reach 1Mbit/s
Infrared interface (IrDA): the rate is also 115kbit/s, generally laptops have this interface
Universal Serial Bus USB: A plug-and-play interface standard that supports hot swapping. USB1.1 rate up to 12Mbit/s, USB2.0 up to 480Mbit/s
IEEE1394 (FireWire) interface (also known as ilink): its transmission rate can reach 100M~400Mbit/s

6. Further understanding of the camera
From the perspective of the composition of the camera, the quality of a camera is mainly determined in terms of hardware:
1. Lens (LENS)
The composition of the lens is a lens structure, which consists of several lenses, generally plastic or glass. Usually the lens structure of the camera is: 1P, 2P, 1G1P, 1G2P, 2G2P, 4G and so on. The more lenses, the higher the cost; glass lenses are more expensive than plastic. Therefore, a good-quality camera should use a glass lens, and the imaging effect will be better than that of a plastic lens. In order to reduce costs, most camera products on the market generally use plastic lenses or semi-plastic and semi-glass lenses (ie: 1P, 2P, 1G1P, 1G2P, etc.). 2. Image sensor (SENSOR)

2. Image sensors are divided into two categories: CCD (charge couple device): charge coupled device. CMOS (complementary metal oxide semiconductor): complementary metal oxide semiconductor

The advantages of CCD are high sensitivity, low noise and high signal-to-noise ratio. However, the production process is complicated, the cost is high, and the power consumption is high. The advantages of CMOS are high integration, low power consumption (less than 1/3 of CCD), and low cost. However, the noise is relatively large, the sensitivity is low, and the light source requirements are high.
Under the same pixel, the CCD imaging often has good transparency and sharpness, and the color reproduction and exposure can be guaranteed to be basically accurate. It is also the future development trend;

3. More user-friendly, easier to use, and more practical application functions are the real needs of customers. "Daily Use Precautions"

1. When using the camera daily, you should pay attention to the following points:

a. Do not point the camera directly to the sun, so as not to damage the image sensing device of the camera.

b. Avoid contact between the camera and oil, steam, moisture, moisture and dust, and avoid direct contact with water.

c. Do not use harsh cleaners or organic solvents to wipe the camera.

d. Do not pull or twist the cable, similar actions may cause damage to the camera.

e. If it is not necessary, do not open the camera at will and try to touch its internal parts, which will easily cause damage to the camera.

f. The camera should usually be stored in a clean and dry place.

1. Photosensitive element

At present, the photosensitive elements used in mainstream cameras on the market are mainly CCD and CMOS. They act like the negatives in a conventional camera. CCD has high resolution and vivid color reproduction, and has become the protagonist of megapixel digital photographic equipment; compared with CCD, CMOS has the characteristics of energy saving and low cost, so almost all low-end cameras use CMOS as the photosensitive element .

The disadvantage of CMOS camera is that it has higher requirements on light, and the effect of the generated image is rougher than that of CCD. Some readers may notice that some high-end digital SLR cameras also use CMOS sensor, but the two are technically different. Moreover, for the camera, the effect is often not the most important, and the effect of the cheap CMOS camera is acceptable.

2. Pixel value and resolution

Pixel value and resolution The resolution here refers to the optical resolution, which are two important indicators of the camera. Pixel value refers to the number of independent pixel points in the image, which is determined by CCD or CMOS. The larger the pixel value, the stronger the image analysis ability.

The pixel values ​​of current mainstream camera products are generally 300,000, 350,000 and 380,000, and there are also 500,000 or even 1.3 million, but they are relatively rare and the price is high. Resolution is the ability of a camera to distinguish an image, and its maximum value is determined by the camera's pixel values ​​(except for interpolation).

For example, the current 300,000-pixel camera can provide a maximum resolution of 640 × 480, but the default resolution supported by many chat software (such as MSN) is only 320 × 240, which is equivalent to 100,000 pixels. The author would like to point out that a large pixel value only means that the image will be more delicate and clear in theory, but the pixel value is not the only factor that determines the imaging quality.

In addition, when purchasing, you should also ask whether the nominal pixel value is a real pixel or an interpolation, because there is a huge difference between the two in terms of cost and effect. What is an interpolated pixel? An interpolated pixel is a "missing" pixel that is calculated mathematically on the basis of surrounding pixels.

There are many cameras on the market that only sell for tens of yuan in this way to deceive consumers. Although they are also nominally 300,000 pixels, their real pixels are only 100,000. Of course, it is not very reliable to ask the merchants, and sometimes they themselves are "victims" (only the manufacturers know). In fact, the imaging effect of 100,000 pixels and 300,000 pixels is obviously different. From the color saturation and the clarity of the picture, the naked eye can distinguish it.

3. Maximum frame rate

In addition to pixel value and resolution, the frame rate when shooting is also an important factor in determining the quality of the picture. You can understand it as how many pictures the camera samples per second. This makes it easy to understand: the higher the sampling rate, the smoother the image will of course be. In practical applications, only when the frame rate of the screen refresh is more than 24 frames per second, the human eye will not notice the obvious pause.

Due to cost constraints, the maximum frame rate of mainstream cameras is mostly 30 frames per second, and low-end products are only 15 frames per second or even lower. A camera with better performance should have a maximum frame rate of 30 frames per second (352×288), and even if it shoots in standard VGA format (640×480), it should have a refresh rate of 15 frames per second.

4. Lens and focal length

The position of the lens in the camera is equivalent to the human eye. Whether the captured image is bright and clear often depends on the quality of the lens. The cost of the lens accounts for a large proportion of the entire camera. Therefore, two cameras with the same pixel and the same function use different lenses, and the cost may vary greatly. Products that use cheap plastic lenses, for example, are cheaper.

It is generally accepted that a better lens should be made of glass or fiberglass and consist of multiple lenses. Whether the coating is also a factor to evaluate the quality of the lens, how to tell whether the lens is coated or not? It is very simple, from the side, the coated lens has purple or blue-green (the color of refraction is also different depending on the coated film) gloss , and the uncoated ones do not have these luster at all.

Some users find that the image is very blurry only after they buy the camera, but when they tried it at the merchant, it was fine. Like point-and-shoot cameras, the camera uses a hyperfocal distance, which has a large depth of field but should be manually adjusted for macros. Therefore, it is sometimes necessary to manually adjust the focus of the camera to get the clearest image.

Tip: Because the depth of field behind the lens is relatively large, people call the distance after the focus point that the image can be clearly imaged as the hyperfocal distance. Applying a hyperfocal distance is the quickest way to achieve maximum depth of field or control the range of sharpness in an image. The point-and-shoot camera generally uses the hyperfocal distance, and the short-focus lens can image the scene more clearly after a certain distance, omitting the focusing function.

5. Processing chip

The chip is also a very important factor affecting the imaging effect. For example, the poor quality of the chips used in some products will cause the camera to be unusable at all in poor lighting conditions. We have no way of knowing which processing chip a camera uses unless it is disassembled and inspected, and can only be judged by the actual effect. What is a CMOS camera?

The main difference between CCD and CMOS in manufacturing is that CCD is integrated on a semiconductor single crystal material, while CMOS is integrated on a semiconductor material called metal oxide, and there is no essential difference in the working principle. Only a few CCD manufacturers such as Sony and Panasonic have mastered this technology. Moreover, the CCD manufacturing process is more complicated, and the price of the camera using CCD will be relatively expensive. In fact, after technological transformation, the gap between the actual effect of CCD and CMOS has been reduced a lot. Moreover, the manufacturing cost and power consumption of CMOS are much lower than that of CCD, so many camera manufacturers use CMOS photosensitive elements. Imaging: Under the same pixel, the imaging transparency and sharpness of the CCD are very good, and the color reproduction and exposure can be guaranteed to be basically accurate. However, CMOS products tend to have average transparency, weak color reproduction capabilities for physical objects, and poor exposure. Due to their own physical characteristics, there is still a certain distance between the image quality of CMOS and CCD. However, due to its low price and high integration, it is still widely used in the field of cameras.

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