Basic knowledge of image sensor and image processor

The photosensitive unit of a traditional film camera is a film, and the image sensor is like the photosensitive film of a digital camera. The main function of the image sensor is to feel light and shadow information. The main role of the image processor is to process data. Image sensors and image processors are the core components of digital cameras and the heart of digital cameras.

Digital cameras have two different image sensors: CCD and CMOS image sensors. These two image sensors are two completely different types of semiconductor devices. CCD is called a charge coupler. It is a silicon oxide semiconductor device. It has been widely used for a long time, and its production process is relatively mature. CMOS image sensors and CCD are completely different. They are complementary metal oxide semiconductor devices, which transfer data faster. The power consumption is smaller and the manufacturing cost is relatively low. These two different types of image sensors are used in digital cameras, and the use of CCDs in portable digital cameras is more widespread. Canon EOS digital SLR cameras, from the EOS launched in 2002 called EOS-1Ds, all adopt Canon's independent research and development of CMOS image sensors.

A unit in the image sensor, that is, a pixel, is composed of a photodiode and corresponding control circuit. If the resolution of the image sensor is 5 million pixels, this image sensor integrates more than 5 million photodiodes and related circuits. The photodiode receives the light information of the light and dark changes of the captured image, and converts it into a change in current strength. Then, the analog-to-digital conversion circuit converts the analog current signal into a digital electrical signal, thereby completing the process of converting light and shadow information into digital information. It should be noted here that although the photodiode can sense light information, the photodiode is color-blind and can only feel the change of light and dark, and cannot perceive the color of the subject. In order to obtain color images, people install color filters of different colors on each photodiode. The color filters can use three primary colors: red, green, and blue. Then divide the photodiodes into three categories, and install red, green, and blue color filters respectively. The distribution ratio of the three primary color filters: green 50%, red and blue 25% each. Because each photodiode can only be equipped with a color filter, accepting light of one color, and the result of the overall synthesis of the three primary colors, the resulting image is colored. In addition, the color filter has a type assigned according to complementary colors: yellow, magenta, and cyan.


(Figure 1, the comparison of image sensor and 135 film imaging area: full-frame and 135 film imaging area is the same (36 * 24 mm), Canon EOS-1D MarkllN CMOS image sensor 28.7 * 19.1 mm (yellow),
Canon EOS 30D CMOS image sensor 22.5 * 15.0 mm (blue), 2/3 inch image sensor 8.8
* 6.6 mm (orange), 1 / 1.8 inch image sensor 6.9 * 5.2 mm (pink). )

Pixels are only an important parameter of an image sensor. However, in the image quality setting of a digital camera, it is also allowed to set several different image resolutions, among which the setting of the highest image resolution is equal to the effective pixels of the camera image sensor. However, the level of the image resolution setting does not mean the quality of the image captured by the digital camera. As long as the shooting method is proper, various image resolution settings with different heights can get clear images. The resolution of the captured image only means the difference in the limit size of the output photo. Also, the higher the image resolution setting, the larger the size of the output photos. For example: 2048 * 1536 (3 million pixels) can output high-quality photos in A4 format, and 3072 * 2304 (7 million pixels) can output A3 format. High-quality photos. Therefore, when purchasing a digital camera, you can select the effective pixels of the image sensor of the digital camera according to the size of the photo that you often need to output. From a practical point of view, it is not necessary to excessively pursue high pixels, for example, it is generally used as a digital camera for home use, and more is to take family commemorative photos and travel commemorative photos. The purpose of taking this type of photo is usually just to output a small size photo of 5 to 7 inches, not to mention blindly pursuing a high-resolution digital camera.



(Figure 2, CMOS image sensors independently developed by Canon Digital: EOS-1D Markll (top left), EOS-1D MarkllN (top middle), EOS 5D (top right), EOS 30D (bottom left), EOS 350D (bottom right).

When choosing a digital camera, in addition to the effective pixels of the image sensor, the factor that should be more concerned is the size of the image sensor. When most people choose a digital camera, they are concerned about the effective pixel height of the image sensor of the digital camera, while ignoring the effect of the size of the image sensor on the imaging quality of the digital camera. There are many different sizes of image sensor sizes. In Canon compact digital cameras, CCD image sensors often used have different size specifications such as 2/3, 1 / 1.8, 1 / 2.5, and 1/3 inches, among which PowershotPro1 is used The 2 / 3-inch CCD image sensor is the largest, and the 1 / 3-inch CCD image sensor used by PowershotA42O is the smallest. The CMOS image sensor of Canon EOS digital SLR camera has three different specifications. The first type is Canon EOS-IDs Markll CMOS image sensor and 135 film imaging area (36 * 24 mm) are the same; EOS 5D CMOS image sensor and EOS- 1DSMarkll is similar, 35.8 * 23.9mm, both belong to the full-frame series; the second category is EOS-1DMarkllN CMOS image sensor with an imaging area of ​​less than 135 film, 28.7 * 19.1mm, belonging to the APS-H series; the third category is EOS 30D The CMOS image sensor is smaller, 22.5 * 15 mm; the CMOS image sensor of EOS 30D is similar to EOS 30D, 22.2 * 14.8 mm; both belong to the APS-C series. The difference in image sensor size, the imaging quality is There is an impact. If the effective pixels of the digital camera image sensor are the same, the larger the image sensor size, the better the imaging quality. This is because the larger the image sensor size, the larger the size of each pixel unit. The larger the size of the pixel unit, the more light and shadow information received, and the richer the information recorded in the final captured image, the image is noisy and other noise The smaller the interference, the better the image quality.



(Figure 3, the second-generation image processor independently developed by Canon: DiGiCll)

Like the image sensor, the image processor is the core component of a digital camera. The extended functions of the digital camera are very rich, and various settings, white balance, image quality parameters, etc. can be adjusted at will as needed. The realization of these functions depends on the image processor. DiGiC is an image processor dedicated to digital cameras independently developed by Canon. Not only can it process image data, but it can also control functions such as camera storage, automatic exposure, and automatic focusing. Since the launch of the compact digital camera PowerShot G3 in 2002 and the digital SLR camera EOS 10D in 2003, Canon ’s DiGiC image processor has been put into practical use. DiGiC ll is already the second generation of new image processor with better performance. Canon independently developed CMOS image sensors and DiGiC ll image processors, which have been fully used in EOS digital SLR cameras. Therefore, Canon has mastered the core technology of digital SLR cameras. Not only that, but Canon has also applied the DiGiC ll image processor to all new compact digital cameras. That is to say, Canon's digital cameras have adopted DiGiC ll's new image processor throughout.

The practical application of DiGiC ll's new image processor has greatly improved the performance of Canon digital cameras. EOS 300D is the world's first million-dollar digital SLR camera, once famous and extremely influential. EOS 350D is an updated product of EOS 300D. EOS 300D uses the old DiGiC image processor, while EOS 350D uses the new DiGiC ll image processor. As a result, the performance of the EOS 350D has been greatly improved compared to the EOS 300D: first, from the perspective of imaging quality, the photos taken by the EOS 350D are cleaner and have less noise that affects the imaging quality; In addition, the boot time and shutter lag are significantly improved over the EOS 300D. The EOS 350D takes only 0.2 seconds to start shooting, the shutter lag is only 100 milliseconds, and the capture of dynamic targets is more calm; moreover, the EOS 350D consumes less power. Although the EOS350D uses a smaller capacity NB-2LH lithium battery (720 mAh), it can still take as many photos as the EOS 300D with a larger capacity BP-511 lithium battery (1100 mAh). .

From this point of view, the application of DiGiC ll's new image processor can not only improve the imaging quality of digital cameras, but also further accelerate the processing speed of digital cameras, but also reduce the power consumption of digital cameras and extend battery life. In short, DiGiC ll's new image processor can significantly improve the overall performance of digital cameras.

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