Mentioned digital cameras, digital cameras have to say is the heart - the photosensitive element . Compared with a conventional camera, a conventional camera using the "film" as the vector information is recorded, and a digital camera "film" which is the image forming photosensitive member , and is integral with a camera, digital camera heart. Photoreceptors is at the heart of digital cameras, is the most critical technology. Digital camera path of development, it can be said that the development path of the photoreceptor. Core of the current imaging member a digital camera, there are two: one is the CCD (charge-coupled) devices are widely used; the other is a CMOS (Complementary Metal Oxide Semiconductor) device.
Photosensitive member works
charge coupled device image sensor CCD (Charge Coupled Device), which uses a high sensitivity semiconductor material made of light into electric charge can, through analog to digital converter chip into a digital signal, a digital signal after compressed by the inside of the camera after the flash memory storage cards or internal hard disk, it is possible to easily transfer the data to the computer, and the computer by means of processing means, according to need to modify the image and imagination. CCD by a number of sensitive units, usually in megapixels units. When the CCD surface exposed to light, the charge of each photosensitive unit will be reflected in the assembly, all of the signals generated by the photosensitive units together, constitute a complete picture.
Compared to traditional film and CCD, CCD is closer to the human eye's visual work. But, the human eye's retina is responsible for the light intensity of the induced stem cells and cone cells of the color sensing, visual sensing composition division of labor. CCD After more than 35 years of development, roughly the shape and mode of operation have been finalized. CCD composed mainly by a similar mosaic grid, concentratingLenses and pads on the bottom of most of the electronic circuit matrix components. CCD is currently capable of producing companies are: SONY, Philps, Kodak, Matsushita , Fuji and Sharp, most of the Japanese manufacturers.
Complementary metal oxide semiconductor CMOS (Complementary Metal-Oxide Semiconductor) and CCD may be the same as a semiconductor light changes recorded in the digital camera. CMOS manufacturing technology and general computer chips no difference, mainly using both silicon and germanium semiconductor elements made so on coexist with a CMOS N (with - e) and P (+ electrical tape) stage the semiconductor, which current is generated by two complementary effects can be interpreted as chip records and images. However, CMOS drawback is too prone to miscellaneous point, mainly because of early design of the CMOS in dealing with rapidly changing images, due to the current change too frequently and produce overheating.
Difference between the two photosensitive elements
can be seen by the working principles of the two photosensitive elements, CCD has the advantage of image quality is good, but due to the complex manufacturing process, only a handful of companies able to master, thus resulting in high manufacturing costs, especially large CCD, the price is very high. At the same time, the past few years, CCD 300,000 pixels from the beginning, has been developed to 600 million and increase the pixel has reached a limit.
In the same resolution, CMOS cheaper price than CCD, but CMOS devices resulting image quality is lower compared to CCD is. So far, the vast majority of the market and high-end consumer-level digital cameras use CCD as sensors; CMOS sensor is used in some low-end products as the camera head, if Which camera manufacturers use CCD camera asking for too much sensors, manufacturers will spare no effort to its hype as a selling point, even as a "digital camera" in the name. For a time, whether the CCD sensor into one of the people to determine the grade of standard digital camera.
CMOS image sensorOne advantage is that the power consumption is lower than the CCD, CCD to provide excellent image quality, i.e., pay higher power consumption, as the charge transport smooth, noise reduction, the need to improve the effect of the pressure differential transmission. But CMOS image sensors of each pixel charge into a voltage, amplifies put before reading, can be driven by a 3.3V supply, power consumption is lower than the CCD. CMOS image sensor further advantage is integrated with the peripheral circuit is high, the ADC may be integrated signal processor, so that the volume significantly reduced, e.g., CMOS image sensor, only one set of power, but the CCD need three or four set of power due to the different processes and the CCD signal processor and the ADC, to reduce the volume of the CCD package is difficult. But the problem CMOS image sensor primary solution is to reduce noise generation, whether future CMOS image sensor can be changed long been repressed CCD fate, the future development of technology is the key.
Factors affecting the sensor
for digital cameras, image sensor imaging element has two main aspects: First, the area of the photosensitive member; the second is the photosensitive element of color depth .
The larger the area of the photosensitive member, a larger image, under the same conditions, to record an image more detail, the interference between pixels is small, the better the image quality. But with the stylish compact digital camera to develop in the direction of an area sensor can only be getting smaller and smaller.
In addition to the area, there is an important indicator of the photosensitive element, that is, the color depth , which is a bit of color, that is, the number of bits with binary digits to record the three primary colors. Non-professional digital cameras are typically photosensitive member 24, the high point of sampling was 30, while the recording is still 24, professional digital camera imaging device is at least 36, is said to have 48 the CCD. For 24-bit device, the luminance value of the light sensing unit can record a maximum of 256 = 2 ^ 8, each of the primary colors with a 8-bitBinary digits to represent up to record 256x256x256 colors is about 16,77 million. For device 36, the luminance value of the light sensing unit can record a maximum of 2 ^ 12 = 4096, each of the primary colors with a 12-bit binary number to represent color is to record up to approximately 6.87 billion kinds 4096x4096x4096 . For example, if a subject is, the luminance of the brightest portion is 400 times the darkest luminance portion with the photosensitive member 24 using a digital camera to shoot, and if parts at low light exposure, than all luminance 256 parts of the preparation, are overexposed, the level of loss, a bright spot is formed, if the press highlight portion is exposed, the entire portions of the certain luminance underexposed, if used professional digital camera 36 of the photosensitive element, will not there is such a problem.
Development of photosensitive element
CCD 1969 by the US Bell developed out of the lab. In the 1980s, although the CCD image sensor is defective, due to the ongoing research has finally overcome the difficulties, but after half of the 1980s to create a high-resolution and high-quality CCD. In the 1990s produced megapixels of high-resolution CCD, CCD development at this time is leaps and bounds, calculate CCD development so far there are more than twenty years. Into the mid-1990s, CCD technology has been rapid development, at the same time, CCD unit area is also getting smaller and smaller. However, while CCD area to improve the image quality of the reduced image, SONY 1989 developed SUPER HAD CCD, the new photosensitive member is reduced in a case where CCD area, relying magnification CCD internal amplifier assembly enhance image quality. After have appeared NEW STRUCTURE CCD, EXVIEW HAD CCD, four-color filter technology (applied specifically for SONY F828). Fuji digital camera is using the Super CCD (Super CCD), Super CCD SR.
For CMOS, it has the ease of mass production, and fast, low cost, will be the key to the development direction of digital camera devices. Currently, under CANON, and other company's continuous efforts, the new CMOS devices continues to introduce new, high dynamic range CMOS devices has emerged, this technology eliminates the need for shutter, aperture, automatic gain control and gamma correction, bringing them closer to the the CCD image quality. In addition, as CMOS inherent plasticity, you can make a high-pixel CMOS sensor and large costs do not rise much. Relative stagnation compared to CCD, CMOS as a new thing and demonstrated vigorous vitality. As a core component of a digital camera, CMOS photoreceptors to gradually replace the trend has been the CCD sensor, and hopefully become the mainstream of photoreceptors in the near future.
