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Image operation -------------- A. [Exposure] Optical signals into electrical signals by discrete pixels When the incident light in the form of photons fall on the pixel array, an image. Each photon energy corresponding to the silicon absorption of the reaction (electron - hole) power group, the number of electrons each pixel can be collected depends on the light level and exposure time, linear, nonlinear depends on the wavelength. -------------- Two. The power transfer Power transfer within the CCD. Once the power was concentrated and kept in the pixel structure, must make in the physical separation and pixel detection amplifier power when a pixel power moves, while the corresponding pixel of electricity are moved. Power voltage conversion and output amplification ========================= [Digital camera CCD structure] -------------- The first layer of micro-lens] We know that the key to a digital camera imaging is its photosensitive layer, must be extended in order to expand the lighting rate of the CCD, the light-receiving area of ??a single pixel. Way to improve the lighting rate is also easy to make quality decline. This layer "micro lens" is equivalent to that in front of the photosensitive layer with a pair of glasses. Sensitive area is no longer because of the opening area of ??the sensor and decided instead to determine the surface area of ??micro-lens. -------------- Second layer of dichroic filter.] The second layer of the CCD is "dichroic filter" There are two separations way, one RGB primary color separation method, the other is CMYK fill color separation method Both methods have their advantages and disadvantages. 1 RGB or RGB color separation method Almost all human spectacles can identify the color can be red, green and blue components, the RGB three letters Red Green and Blue, indicating that the RGB color separation method is made through three channels of color adjustment . 2. CMYK This is a tie made by the four-channel color, they are green (C), magenta (M), yellow (Y) and black (K). In the printing industry, CMYK is more applicable, but its less than the RGB color adjustment out. The primary color CCD advantage of the sharp picture quality, true color, but the disadvantage is that the noise problem. Therefore, we can generally use the primary color CCD digital camera, would be unlikely to more than 400 ISO sensitivity. In contrast, the complementary color CCD more yellow color filter of a Y on the resolution of the color carefully, but at the expense of a part of the image resolution, ISO value, the complementary color CCD can tolerate a higher sensitivity, are generally can be set at more than 800 -------------- Third layer photosensitive layer] The third layer of the CCD is a "sensitive film, this layer is mainly responsible for through the color filter layer of the light into electronic signals, and transmit the signal to the image processing chip, the image restore. Traditional camera film size of 35mm, 35mm diagonal length, 35mm film of the photosensitive area of ??36 x 24mm. The larger the size of the conversion to digital cameras, the diagonal length of around 35mm, CCD / CMOS. SLR digital camera, have close to 35mm size of the CCD / CMOS, compared to consumer digital camera to be much larger. ========================= [The CCD VS COMS] CCD and CMOS sensors are currently being widely used by the two image sensors [Same] - The use of light-sensitive diode (photodiode) for photoelectric conversion, convert images to digital data [Difference] - Digital data transmission in different ways. Different ways of data transfer, performance and applications of CCD and CMOS sensors are also many differences. CCD sensors are superior in terms of sensitivity, resolution, noise control CMOS sensor The CMOS sensor has a low cost, low power, highly integrated features. However, with advances in CCD and CMOS sensor technology, the difference between the two there is a diminishing trend. -------------- (1) [sensitivity] CMOS sensor, each pixel of four transistors and a photosensitive diode, making the sensitive area of ??each pixel is much smaller than the pixel surface area, so in the case of the same pixel size, the sensitivity of the CMOS sensor to lower than the CCD sensor. -------------- (2) the cost difference] The peripheral circuits of the CMOS sensor using a semiconductor circuit is the most commonly used CMOS process, (1) can easily be integrated into the sensor chip, thus saving the cost of peripheral chips; (2) due to CCD charge transfer of the transmitted data, which a pixel can not run, it will lead to a whole row of data can not be transmitted, and therefore control the CCD sensor yield a lot more difficult than the CMOS sensor, CCD sensor the cost will be higher than the CMOS sensor. (3) CMOS standard process technology, the use of existing semiconductor devices without additional investment in equipment and quality As semiconductor technology advances. (4) At the same time, global fab CMOS production line more future production also help lower costs. (5) CMOS sensor, the biggest advantage is it has a high degree of system integration conditions. In theory, the functionality required of all image sensors, such as vertical displacement, horizontal displacement registers, timing control, CDS, ADC, ..., etc., can be placed on the integration on a chip, and even all the chips, including back-end chip (Back-end Chip), flash memory (Flash RAM) can also be integrated into a single chip (SYSTEM-ON-CHIP) in order to achieve the purpose of reducing the cost of machine production. (6) the price 1/3 cheaper than CCD -------------- (3) [resolution] CMOS sensor, each pixel than CCD sensor complex, the pixel size is difficult to achieve the level of the CCD sensor, therefore, when we compare the same size CCD and CMOS sensor, a CCD sensor resolution is usually better than CMOS the level of the sensor. -------------- (4) [noise] CMOS sensor, each light-sensitive diodes are required to be used with an amplifier, and amplifier are analog circuits, it is difficult to make the results obtained by each amplifier consistent with only one amplifier on the edge of the CCD sensor chip compared, CMOS sensors The noise will increase, affecting the image quality. -------------- (5) Power consumption] CMOS sensor, the image capture mode is active, the charge generated by the light-sensitive diode transistor amplifier output, the CCD sensor for passive acquisition required applied voltage in each pixel, the charge moves, In addition, the applied voltage is usually needed to achieve 12 to 18V; Therefore, CCD sensor, in addition to the more difficult in the power management circuit design, high driving voltage so that power consumption is much higher than the level of the CMOS sensor. CMOS sensor, small size, power consumption is less than the CCD 1/10 -------------- CMOS than CCD, with: More flexible image capture, higher sensitivity, wider dynamic range, higher resolution, lower power consumption and a more excellent system integration =========================
【Article is excerpted from: Baidu Encyclopedia】 |
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