Why do digital cameras have good ccd sensitivity, while some SLR (such as EOS550D) use coms photosensitive elements?

It can be seen from the working principles of the two photosensitive devices that the advantage of CCD lies in its good imaging quality. However, due to the complex manufacturing process, only a few manufacturers can master it, so the manufacturing cost remains high, especially the large CCD, which is very expensive.

At the same resolution, CMOS is cheaper than CCD, but the image quality produced by CMOS devices is lower than CCD. So far, most consumer-grade and high-end digital cameras on the market use CCD as sensors; CMOS sensors are used as low-end products in some cameras. If any camera manufacturer uses CCD sensor, the manufacturer will spare no effort to promote it as a selling point, and even call it "digital camera". For a time, whether there is a CCD sensor has become one of the standards for people to judge the grade of digital cameras. The main advantage of CMOS used in CCD is very power saving. Unlike CCD composed of diodes, CMOS circuits have almost no static power consumption, only when the circuit is on. This makes the power consumption of CMOS only about 1/3 of that of ordinary CCD, which is helpful to improve people's bad impression of digital camera "electric tiger". The main problem of CMOS is that it is overheated due to too frequent current changes when dealing with rapidly changing images. If the dark current is well suppressed, it is not a big problem, and if it is not well suppressed, it is very easy to get messy. In addition, the image data scanning methods of CMOS and CCD are very different. For example, if the resolution is 3 million pixels, the CCD sensor can scan 3 million charges continuously. The scanning method is very simple, just like passing a bucket from one person to another, and the signal can not be amplified until the last data scanning is completed. Each pixel of CMOS sensor has an amplifier, which converts the charge into an electrical signal. Therefore, CMOS sensor can amplify the signal pixel by pixel, and can save any invalid transmission operation, so it can scan data quickly with little energy consumption and reduce noise. This is Canon's intra-pixel charge transfer technology. Concept and working principle of photosensitive device

Charge coupled device (CCD) is an image sensor of CCD, which is made of highly sensitive semiconductor materials. It can convert light into charge, and the charge is converted into a digital signal through an analog-to-digital conversion chip. The compressed digital signal is saved by the flash memory or the built-in hard disk card in the camera, so the data can be easily transmitted to the computer, and the image can be modified as needed and imagined with the help of computer processing means. CCD is composed of many photosensitive units, usually in millions of pixels. When the CCD surface is illuminated by light, each photosensitive unit will reflect the charge on the module, and the signals generated by all photosensitive units will be superimposed to form a complete picture.

Charge coupled device

Compared with traditional negatives, CCD is closer to the working mode of human eyes visually. The retina of human eye is composed of rod cells responsible for light intensity perception and cone cells responsible for color perception, which work together to form visual perception. After 35 years of development, the general shape and working mode of CCD have been finalized. CCD is mainly composed of a mosaic grid, a condenser lens and an electronic circuit matrix at the bottom. At present, companies capable of producing CCD are Sony, Philips, Kodak, Panasonic, Fuji and Sharp, most of which are Japanese manufacturers.

At present, there are mainly two kinds of CCD photosensitive elements, namely linear CCD and area CCD. High-resolution still camera uses linear CCD, which only takes one line of images at a time, which is the same as the method of scanning photos with flat scanner. This kind of CCD has high precision and slow speed, so it can't be used to shoot moving objects or flash.

Matrix CCD, in which each photosensitive element represents a pixel in the image, when the shutter is opened, the whole image is exposed at the same time. Generally, there are two methods to process colors by area CCD. One is to embed color filters in CCD matrix and use different color filters for similar pixels. There are two typical arrangements, G-R-G-B and C-Y-G-M, and the imaging principles of these two arrangements are the same. In the process of recording photos, the microprocessor inside the camera obtains signals from each pixel and synthesizes four adjacent points into one pixel. This method allows instant exposure and the microprocessor can run very fast. This is the imaging principle of CCD in most digital cameras. Because it is not synthesized at the same point, which involves mathematical calculation, the biggest defect of this CCD is that the image it produces can never be as sharp as a knife.

Complementary metal oxide semiconductor

Complementary metal-oxide semiconductor (CMOS), like CCD, is a semiconductor that can record light changes in digital cameras. The manufacturing technology of CMOS is no different from that of general computer chips, mainly using semiconductors made of silicon and germanium, so that semiconductors with N (charged) and P (charged) energy levels are stored on CMOS, and the currents generated by these two complementary effects can be recorded and interpreted as images by processing chips. However, the disadvantage of CMOS is that it is too prone to clutter, mainly because the early design makes CMOS overheat when dealing with rapidly changing images, because the current changes too frequently.

In addition to CCD and CMOS, there is also a super CCD exclusively launched by Fuji Company. Super CCD uses octagonal diodes instead of conventional square diodes, and the pixels are arranged in a honeycomb shape, and the area of each pixel is larger than that of traditional CCD. The result of pixel rotation of 45 degrees can reduce the unnecessary space for image shooting, and the condensing efficiency is relatively high. After the efficiency is improved, the sensitivity, signal-to-noise ratio and dynamic range are all improved.

Each pixel in a traditional CCD consists of a diode, a control signal path and an electric quantity transmission path. Supercode uses honeycomb octagonal diode, which cancels the original control signal path and only needs one direction of power transmission path, so the photodiode has more space. The arrangement structure of super CCD is more compact than that of ordinary CCD, and the pixel utilization rate is higher. That is to say, under the same size, the photodiode of super CCD absorbs more light, which improves the sensitivity, signal-to-noise ratio and dynamic range.

Then why is the output pixel of super CCD higher than the effective pixel? We know that CCD is not sensitive to green, so we use G-B-R-G to synthesize. In fact, some of the synthesized pixels are * * *, so there is a certain gap between the imaging quality and the ideal state, which is why some high-end professional digital cameras feel RGB tricolor light with 3CCD respectively. Super CCD realizes the equivalence of R, G and B pixels by changing the arrangement relationship between pixels, and it also takes three pixels as a group when synthesizing pixels. So the traditional CCD synthesizes four pixels. In fact, only three pixels are needed, which wastes one. But the super CCD found this, and only three pixels can be used to synthesize a pixel. In other words, CCD synthesizes a pixel every 4 points, and each point is calculated 4 times; Supercode synthesizes a pixel every three points, and each point is calculated four times, so the utilization rate of supercode pixels is higher than that of traditional CCD, and more pixels are produced.

SLR digital camera SLR digital camera refers to a single-lens reflex digital camera, that is, digital, single lens, lens and reflex. At present, the common SLR digital camera brands on the market are Nikon, Canon, Pentax, Fuji and so on.

Working principle:

In the working system of SLR digital camera, after the light reaches the reflector through the lens, it is refracted to the focusing screen above to form an image. Through the eyepiece and pentaprism, we can see the scenery outside in the observation window. In contrast, ordinary digital cameras can only see the captured images through the LCD screen or electronic viewfinder (EVF). Obviously, the directly seen image is more conducive to shooting than the processed image.

When shooting in DSLR, press the shutter button, the reflector will pop up, and the shutter curtain in front of the photosensitive element (CCD or CMOS) will be opened at the same time, and the light passing through the lens will be projected onto the photosensitive original, and then the rear reflector will be restored immediately, and the image can be seen in the viewfinder. This structure of the single-lens reflex camera ensures that it is shot through the lens, so that the image seen in the viewfinder is always consistent with the image on the film, and its framing range is basically consistent with the actual shooting range, which is very conducive to intuitive framing and composition.

Main features:

A major feature of SLR digital cameras is that they can change lenses of different specifications, which is an inherent advantage of SLR cameras and incomparable to ordinary digital cameras.

In addition, the SLR digital camera is now positioned in the high-end products of digital cameras, so in terms of the area of photosensitive elements (CCD or CMOS) related to the photographic quality of digital cameras, the area of SLR digital cameras is much larger than that of ordinary digital cameras, which makes the photosensitive area of each pixel of SLR digital cameras much larger than that of ordinary digital cameras, so each pixel can show more detailed brightness and color range, which makes the photographic quality of SLR digital cameras significantly higher than that of ordinary digital cameras.