Photographic terminology: CMOS image sensor

Photographic terminology: CMOS image sensor

CMOS image sensor is a typical solid-state imaging sensor, which has a common historical origin with CCD. CMOS image sensor is usually composed of image sensor array, row driver, column driver, timing control logic, AD converter, data bus output interface, control interface and so on, which are usually integrated on the same silicon chip. Its working process can generally be divided into reset, photoelectric conversion, integration and reading.

Photographic terminology: CMOS image sensor

Application of CMOS image sensor

1. Digital camera

People have been using film cameras for hundreds of years. Since 1980s, people have developed filmless CCD digital cameras with high technology. The traditional film camera has undergone fundamental changes. The appearance of electrically writable and controllable cheap FLASH ROM, and the appearance of low-power and low-cost CMOS camera. It opens up a new situation for digital cameras. The functional block diagram of the digital camera is shown on the right below.

As can be seen from the figure, the internal device of a digital camera is completely different from that of a traditional camera. Under the control of electronic shutter, a color CMOS camera takes a picture and stores it in DRAM, and then in flash ROM. According to the capacity of FLASH ROM and the compression level of image data, the number of photos can be determined. If ROM is replaced by PCMCIA card, the capacity of digital camera can be expanded by changing the card. Just like changing film, the digital image information of digital camera is transferred to the hard disk of PC for storage, which greatly facilitates the storage, retrieval, processing, editing and transmission of photos.

2.CMOS digital camera

The USB camera introduced by Omni Vison Company in the United States consists of OV76 10 CMOS color digital image chip, OV51advanced camera and USB interface chip, and the resolution is as high as 640 x 480, which is suitable for video systems transmitted through universal serial bus. With the introduction of OV5 1 1 advanced camera, PC can get a lot of video information in real time, and the compression ratio of its compression chip can reach 7: 1, thus ensuring the rapid transmission of images from image sensor to PC. For CIF image format, OV5 1 1 can support the transmission rate as high as 30 frames per second, which reduces the image jitter that usually occurs in low bandwidth applications. OV5 1 1 as a controller of high-performance USB interface is flexible enough to be suitable for applications including video conferencing, video mail, computer multimedia and security monitoring.

Is the camera CCD camera or CMOS camera?

The main difference between CCD and CMOS in manufacturing is that CCD is integrated on semiconductor single crystal material, while CMOS is integrated on a semiconductor material called metal oxide, and there is no essential difference in working principle. Only a few CCD manufacturers, such as Sony and Panasonic, have mastered this technology. Moreover, the manufacturing process of CCD is complex, and the price of cameras using CCD will be relatively expensive. In fact, after technical transformation, the gap between CCD and CMOS has narrowed a lot. Moreover, the manufacturing cost and power consumption of CMOS are much lower than that of CCD, so many camera manufacturers adopt CMOS photosensitive elements.

Imaging: In the same pixel, CCD has good imaging transparency and clarity, and color reproduction and exposure can ensure basic accuracy. However, CMOS products often have general permeability, weak color reproduction ability and poor exposure. Due to its own physical characteristics, the imaging quality of CMOS is still far from that of CCD. But because of its low price and high integration, it has been widely used in the field of cameras.

What is the difference between CCD and CMOS?

Q: Since ccd and cmos are photosensitive sensors, why is the price difference so big? What's the difference between them? For ordinary novice digital cameras, should we consider their performance?

A: CCD is a mature imaging device at present, and CMOS is considered as the future imaging device.

Because the CMOS structure is relatively simple, it is the same as the existing large-scale integrated circuit production process, so the production cost can be reduced. In principle, CMOS signal is a point-based charge signal, while CCD is a line-based current signal. The former is more sensitive, faster and more energy-saving. At present, advanced CMOS is not worse than ordinary CCD, but CMOS technology is not very mature, and ordinary SMOS generally has low resolution and poor imaging.

At present, many low-end entry-level digital cameras use cheap low-end CMOS chips, and the imaging quality is relatively poor. Popular, advanced and professional digital cameras use different grades of CCD, and individual professional or quasi-professional digital cameras use advanced CMOS chips. X3 chip, which represents the future development of image technology, is actually a CMOS chip.

It is impossible to generalize which is better between CCD and CMOS, but generally speaking, the CCD chip used by mass digital cameras has better imaging quality.

Bad points and repair problems of CCD?

When shooting at night or covering the lens cover for a long time, the spots on the image are not necessarily CCD bad spots, but some are noise, which will be improved after lowering the CCD temperature, and some can also be improved by firmware upgrade.

If the CCD is really defective, it can be said that it can't be repaired, because it is a hardware problem of the CCD. It is almost impossible and uneconomical to repair the imaging unit of CCD just to replace the camera or CCD.

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