Requirements: IPC HD Camera Knowledge Reserve
Content: The first part analyzes the advantages and disadvantages of CCD sensor and CMOS sensor from four aspects
The second part analyzes the technical parameters of the digital camera
Organize the poems from: Time
The first part analyzes the advantages and disadvantages of CCD sensor and CMOS sensor from four aspects
From: http://www.elecfans.com/yuanqijian/sensor/20140724349368.html
CCD sensor and CMOS sensor both in the structure, performance and technology are not the same, I will make a simple comparison between the two, so that the vast number of readers of the CCD and CMOS can have a relatively preliminary understanding.
CCD and CMOS sensors are the most common digital image sensors, which are widely used in digital cameras, digital cameras, camera phones and cameras. Both in the structure, performance and technology are not the same, I will make a simple comparison between the two, so that the vast number of readers of the CCD and CMOS can have a relatively preliminary understanding, in the purchase of related products can also be aware of.
structure Comparison of 1 CCD and CMOS sensor
CCD (Charge coupled device), which is a "charge-coupled device", is a photosensitive semiconductor chip for capturing graphics, but the CCD does not have the ability to record graphics data, nor is it capable of permanent preservation, and all graphical data is fed into an analog-to-digital converter without stopping. A signal processor and a storage device. 1970 US Bell Labs invented the CCD. 20 years later, the technology was used to create digital cameras that pushed the image processing industry into a whole new field. CMOS (Complementary Metal Oxide Semiconductor), or "complementary metal oxide semiconductors". It is a kind of important chip in the computer system, which preserves the large amount of data that the system directs. It has been found that CMOS processing can also be used as a sensor in digital cameras, which facilitates mass production and low-cost characteristics are the business of the dream.
The main difference between CCD and CMOS is that the CCD is integrated in the semiconductor single crystal material, and CMOS is integrated in the semiconductor material called metal oxide, the working principle is not the essential difference, it is the photoelectric conversion using the photosensitive diode (photodiode), The principle of this conversion is similar to that of solar cells, the stronger the light, the stronger the electricity, and the weaker the light and the weaker the electricity. According to this principle, the image is converted into digital data, and the main difference is that the digital data is transmitted in different ways.
Comparing the structure of CCD and CMOS, the position and number of ADC (digital-to-analog converter) are the most different. Each time the CCD is exposed, a pixel transfer process is performed after the shutter is closed, the charge signal of each pixel in each row is sequentially passed into the "buffer", amplified by an amplifier at the bottom of the line-guided output to the CCD edge, and the ADC output is concatenated, while the CMOS design is directly attached to the ADC next to each pixel. The charge signal is amplified directly and converted into a digital signal. The reason for this difference is that the special technology of the CCD ensures that the data will not be distorted during transmission, so that the data of each pixel can be aggregated to the edge and then amplified, and the data of the CMOS process will produce noise when the transmission distance is longer, so the data of each pixel must be enlarged before being integrated.
Technical Comparison of 2 CCD and CMOS sensor
CCD storage charge information, need to be under the control of a synchronous signal after the transfer of the read, charge information transfer and read output needs to have a clock control circuit and three different sets of power supply, the whole circuit is more complex and slower. The CMOS sensor directly generates current (or voltage) signal after photoelectric conversion, the signal reading is very simple, but also can process the image information of each unit, the speed is much faster than the CCD. CCD production Technology started early, technically mature, using PN junction or silica (SIO2) isolation layer isolation noise, imaging quality relative to CMOS has a certain advantage. Due to the high CMOS integration, the photoelectric sensor components, the distance between the circuit is very close to each other, light, electricity, magnetic interference is more serious, the noise on the image quality has a great impact, so that the CMOS for a long time can not be put into practical. In recent years, with the continuous development of CMOS circuit denoising technology, CMOS performance has been similar to CCD.
Performance comparison of CCD and CMOS sensor
ISO sensitivity: Since CMOS each pixel consists of four transistors and a photosensitive diode, also includes amplifiers and digital-to-analog conversion circuit, too many additional equipment to reduce the surface area of a single pixel photosensitive area, so the same pixel, the same size, CMOS sensitivity will be lower than the CCD.
Resolution: Since each pixel of a CMOS sensor is more complex than a CCD sensor, its pixel size is difficult to reach the level of the CCD sensor, so when we compare CCD and CMOS of the same size, the resolution of the CCD sensor is usually better than the CMOS sensor.
Noise: Since CMOS each photodiode needs to be paired with an amplifier, if it is megapixel, then more than millions of amplifiers are required, and the amplifier is analog, it is difficult to keep the results of each amplifier consistent, so with only one amplifier on the edge of the chip CCD sensor, compared to The noise of CMOS sensors can be increased by a lot, which affects image quality.
Power consumption: CMOS sensor Image Acquisition mode is active, the electric charge generated by the photosensitive diode will be amplified directly by the next transistor, while the CCD sensor is passive acquisition, the charge must be applied to each pixel to move to the transmission channel. This additional voltage usually needs to be 12~18v, so the CCD must also have a more sophisticated power line design and compressive strength, high drive voltage so that the CCD consumes much more than the CMOS. CMOS consumes only 1/8 to 1/10 of the CCD.
Cost: Because CMOS sensors use the most common CMOS process in general semiconductor circuits, peripheral circuits such as AGC, CDS, Timing generator or DSPs can be easily integrated into the sensor chip, thereby saving the cost of peripheral chips While the CCD transmits the data in the way of charge transfer, as long as one of the pixels can not run, it will result in a whole row of data can not be transmitted, so the control of the CCD sensor yield than the CMOS sensor is much more difficult, even if the experienced manufacturers are difficult to reach 50% of the product in six months, therefore, The cost of manufacturing a CCD sensor is higher than that of a CMOS sensor.
the foreground of 3 CCD and CMOS sensor
CCD is superior to CMOS in image quality, while CMOS has the characteristics of low cost, low power consumption and high degree of integration. However, with the progress of CCD and CMOS sensor technology, the difference will be gradually reduced, the new generation of CCD sensor has been improving the power consumption, and CMOS sensors in the improvement of resolution and sensitivity of the shortcomings. We believe that the continuous improvement of CCD and CMOS sensors will bring us a better digital image world.
the second part analyzes the technical parameters of the digital camera
From: http://www.eccn.com/design_2011121515583035.htm
Objective
With the development of digital technology, digital cameras gradually become a common consumer electronics products. The biggest difference between a digital camera and a traditional camera is that the technical parameters of the digital camera can be set up to capture a more perfect photo, the technical parameters of the digital camera play a decisive role in it, but a lot of consumers do not know the main parameters of the digital camera thoroughly, This has become a hindrance to the purchase of digital cameras a snag, the purpose of this article is to let everyone clear digital camera Several important parameters, can give you a reference to buy DC products.
Technical parameters of digital camera I. CCD
CCD and CMOS are the same photosensitive elements, is the most important part of the digital camera. If the DC itself is likened to a person, then the CCD is like a human brain. Because CMOS is not widely used in consumer-grade digital cameras, we mainly introduce CCD here.
The full name of the CCD is called the charge coupled device, the Chinese name is the charge coupling device image sensor. It is able to convert the light source signal into a charge signal, through the analog to digital converter chip to transform the perfect digital signal, and then after compression by the camera internal memory card to save. The CCD itself consists of a number of photosensitive units, and the basic units are measured in megapixels. When the lens is opened and the CCD surface is illuminated by light, each photosensitive unit will add a different charge signal, adding the charge signals generated by all the photosensitive units together to form a complete digital photograph.
What the average consumer needs to know most is the size of the CCD. Currently on the market, consumer-grade digital cameras are mainly 1/1.8-inch, 1/2.5-inch, 2/3-inch and many other specifications. We judge them only one way, that is, the larger the size of the CCD, the larger the photosensitive area, the corresponding imaging effect is better. For example, a 5 million-megapixel digital camera, the 2/3-inch CCD image must be better than a 1/1.8-inch of the other one. Because if the fixed CCD size to simply increase the pixels, will cause each pixel of the photosensitive area is relatively narrow, they are prone to interference between the phenomenon, thus affecting the final overall imaging effect.
Because of the problem of manufacturing process, the general use of large-size digital camera price is more expensive. In addition, because the size of the CCD directly determines the volume of the camera itself, the general ultra-portable digital camera used CCD size is much smaller than the size of the CCD used in professional-grade digital camera, so the final image will have a relatively large gap.
Technical parameter of digital camera second, lens
The digital camera lens is the second most important element besides the CCD. The interior of the lens is generally composed of many groups of lenses, the material is divided into two types of glass and resin. From the imaging effect, glass-based lenses are better, but the cost of manufacture is higher, and the weight of the lens itself is not guaranteed. The use of more resin lenses on consumer digital cameras, which is thin and light, is relatively easy to make, and as the process continues to improve, the lens of the resin lens is already comparable to the lens of the glass lens in terms of image quality.
Aperture This concept is somewhat difficult to understand, summed up is to use the aperture blade to control the intensity of the light entering the lens, the letter F represents its value, the general consumer digital camera aperture value is generally between f2.8-f11. The general aperture of the adjustment is 1/3 block for stepping, such as from f2.8-f3.5 and so on. We just have to remember: the smaller the aperture value, the more light you have and the more shallow the depth of field. The larger the aperture value, the smaller the amount of incoming light will be, and the depth of field will become larger. The aperture value is inverse proportional to the depth of field.
In general, there are two types of zoom modes on consumer digital cameras: optical zoom and digital zoom. In general, we just need to understand the optical zoom is enough. The principle is to zoom in or out of the object being photographed by moving the lens group. The larger the optical zoom, the farther it can shoot. On a digital camera, the value of the focal length is calculated by converting the values of the 135mm film's traditional camera. 70% of the digital cameras on the market use a commonly used 3 times-fold optical zoom, the individual telephoto DC Optical zoom can be up to 15 times times. But can not be seen in multiples of large, on behalf of can shoot far, or to be based on the actual focus to compare.
In general, digital cameras with telephoto lenses are relatively expensive, and the average player chooses 3 times times the optical zoom DC is fully sufficient.
Technical parameters of digital camera three, light sensitivity
The concept of ISO sensitivity actually comes from the traditional film, which is just an approximate value corresponding to the film sensitivity. From the point of view of the digital camera imaging element, ISO is the measured value of the sensitivity of the Ccd/cmos to the light response. On the digital camera, by adjusting the ISO size, you can change the brightness of the image and the value of the image contrast, in fact, in the digital camera, the light sensitivity is also a control of the image light and dark values.
At present, the ISO value on the consumer digital camera is ISO50, the highest is ISO1600. We should put it in a relatively low position when we take a picture, because the low ISO value can take a clearer, more delicate picture. ISO too high will cause a lot of noise on the image, loss of many image details.
From the application point of view, the high ISO is only suitable for use in the exhibition stage and so on not suitable for using the flash environment, the appropriate increase in the ISO value to increase the brightness of the photo, can be in the dark environment more prominent people and environment, but this value adjustment must be moderate.
Of course, because the professional DSLR camera in the CCD size is much larger than the consumer-grade camera, so at high sensitivity to the noise resistance is much stronger than the ordinary consumer-level DC.
Technical parameters of digital camera four, white balance
The white balance English name is Balance, and its main function is to balance the various color elements in the image according to the different temperature values reflected by the light rays to different objects, resulting in the closest image to the human eye.
Digital camera no matter how the external environment changes, the machine can only recognize the white color, the balance of other colors need to be colored light under the "white" to present other tones. The effect of white balance is to first get the correct white reference color in the photograph, so as to be able to achieve the purpose of restoring other colors smoothly.
Almost all digital cameras now have white balance adjustment, but the white balance itself is closely related to light, so be careful when using the flash. There are many modes of white balance, such as automatic white balance, incandescent white balance, fluorescent white balance, manual white balance and so on.
Regarding the white balance, we just need to pay attention to two points. 1. Avoid the use of automatic white balance in light and complex environments, where the white balance system of the camera becomes ineffective due to the complexity of the light, often resulting in the overall blue color of the image. Red. Green phenomenon. 2. When you do not use flash photography indoors, be sure to choose the incandescent light mode.
Technical parameters of digital cameras v. Shutter
The English name is shutter, and the shutter is a device that controls the effective exposure time of the photosensitive film on the camera. The shutter works like this, in order to protect the camera in the photosensitive device, not exposure, the shutter is always closed, when shooting, adjust the shutter speed, just press and hold the camera's shutter release button (that is, the photo button), between the shutter opening and closing clearance, let the light through the photographic lens, The photosensitive film inside the camera gets the correct exposure, the light passes through the shutter into the photosensitive device, and the memory card is written. As for the common B shutter function of the SLR camera, although it is up to you to decide the duration of the exposure time, the shooting flexibility is higher, but most of the current consumer digital cameras are not yet supported, providing a maximum of 2 seconds, 8 seconds, 16 seconds and other slower speed of the default values. The perfect shutter usually must have the following functions:
1, must have the ability to accurately control the exposure time, which is the most basic role of the camera shutter;
2, must have a high enough shutter speed, in order to facilitate the shooting of high-speed dynamic full or effective control of depth of field;
3, must have the role of long-time exposure, that should be equipped with "T" door or "B" door;
4, with flash synchronous shooting function;
5, with the function of self-timer, in order to make a selfie or in the absence of a shutter line in the case of prolonged exposure, so that the shutter open.
Technical parameter of digital camera VI, display
The biggest difference between a digital camera and a traditional camera is that almost all digital cameras have an LCD LCD screen. The LCD's English is all called Liquid Crystal Display. Its role is mainly to browse pictures and framing. Some ultra-thin digital cameras now almost omit the optical viewfinder, leaving only the LCD screen.
The main technical parameters of the LCD screen are the size of the display and the dimensions of the pixel. Dimensions are measured in inches, such as 1.8-inch, 2.0-inch, 2.5-inch, and so on. There are individual digital cameras that can reach up to 3.5 inches. The larger the area of the LCD screen, the more convenient framing. But it can also cause a steady decline in power.
Also, we can't just look at the size of the LCD screen, its number of pixels is also important. The higher the pixel, the more clearly the image details and colors you can display will appear. Now many large-screen DC, although they all have a 2.5-inch LCD screen, but the relative number of pixels is very low, the image is very grainy, this is not what we want to see.
Technical parameters of digital camera seven, Scene mode
On some auto-exposure digital cameras, there are often many special scene modes. They are based on the manufacturer's settings, in the selected scene automatically adjust the aperture, shutter, focal length, metering method and so on parameters. It is perfectly guaranteed that users who do not understand photography will also be able to take very good photos. The general digital camera needs to have at least four or five kinds of scene mode, the maximum can reach 100 kinds of around. Here are some of the most commonly used patterns
Landscape mode: Use this mode to shoot scenery photos, the camera itself will automatically adjust the aperture to the minimum to achieve maximum depth of field. At the same time the focus distance will also become infinity, so that the photos taken out, all the objects in the picture will become clear.
Portrait mode: If you use it to shoot characters, the camera itself automatically puts the aperture to its maximum for a shallow depth of field effect. A more advanced type of digital camera will also be able to adjust the human skin tone and the overall sharpness of the picture. Even the ability to focus automatically on the face.
Night view mode: We use night-view mode when shooting in the evening. The camera automatically extends the shutter exposure time, which can typically take up to several seconds. To ensure that the photo has enough brightness and contrast. This mode also places the aperture value in a relatively small position, and the flash will automatically close.
Motion Mode: This mode is mainly used to shoot high-speed moving objects, such as athletes, cars and so on. If you use this mode, the camera will automatically adjust the shutter speed to a faster value, usually in 1/500 seconds, or even faster. If the light is low, it also increases the ISO sensitivity accordingly.
IPC Network HD Camera Basics 6 (CCD and CMOS sensors)
