Analysis of mobile phone camera sensors
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We all know that the most important part of determining the image quality of mobile phones and cameras is the photosensitive element. There are two main types of photosensitive elements, one is the CCD sensor and the other is the CMOS sensor. Among them, CCD has good image quality, but the manufacturing process is complicated, there are relatively few manufacturers that can produce it, the price is relatively high (scarcity makes things expensive), and the power consumption is also high, so it is not suitable for use on mobile devices. CMOS sensors have low power consumption, but the image quality level is not as good as CCD. However, with the improvement of technology, the image quality of COMS has gradually caught up with CCD. In addition, at the same resolution, CMOS is cheaper than CCD, so the mobile phone cameras on the market currently use CMOS sensors. Usually CMOS sensors are divided into: back-illuminated CMOS sensors and stacked CMOS sensors. The so-called back-illuminated CMOS sensor is actually the opposite of the traditional front-illuminated CMOS sensor. Simply put, the photodiode and the wiring layer are swapped (as shown in the figure above), so that the light enters the photodiode first, thereby increasing the light sensitivity and significantly improving the shooting effect under low light conditions. As we all know, iPhone 4/4S, Xiaomi 2S, Meizu MX2, and Sony LT26i are all equipped with this type of sensor. The stacked CMOS sensor is a derivative of the back-illuminated CMOS sensor. It is the most widely used and most advanced type in mobile phone cameras and is Sony's exclusive technology. The stacked CMOS sensor uses a chip with a signal processing circuit to replace the original back-illuminated CMOS image sensor's support substrate, and overlaps the pixel part of the back-illuminated CMOS element on the chip, thereby realizing the process of forming a large number of pixels on a smaller chip size. Since the pixel part and the circuit part are independent, the pixel part can be optimized for high image quality, and the circuit part can be optimized for high performance. Finally, the editor would like to say that the photosensitive element is only an indispensable part of the composition of the mobile phone camera, but it is not the decisive factor in the imaging quality of a mobile phone. This also includes the optimization and adjustment of the hardware by the manufacturer through software to make it feel the best effect (this involves the feelings of different people, which depends on the manufacturer's product positioning group). This is also one of the most decisive factors in the difference in the image quality of mobile phone cameras among various manufacturers. Here are some common questions about mobile phone cameras: Why is the camera lens round? The light-sensing element inside is obviously square. On the one hand, the circle can achieve the largest imaging area; on the other hand, it has many optical advantages, such as the round side can reduce the reflection of light; and the round lens is easier to grind, the assembly can be done more accurately, and it is also easy to make various fine adjustments. The most important thing is still the mechanical structure: including fine adjustments such as focus and zoom, it is naturally most convenient to use a spiral push, and the rotation of the round lens will not cause the loss of imaging (if it is a rectangular lens, then, after turning 90°, the 3*2 rectangular photo will be cut into a 2*2 square), which is convenient for the setting of various adjustment mechanisms. Medium and large format lenses need to be matched with different sizes of film/photosensitive elements. Maximizing as much as possible is naturally the most material-saving approach (special-shaped lenses, such as eyeglass lenses, are actually cut from round lenses. For the lens, cutting it off does not help the imaging at all. On the contrary, changing the film may not have enough imaging range, which is a typical thankless task). What is the principle of the application of placing a finger in front of the mobile phone camera and flash to detect heart rate? Use high light (the LED flash next to the camera, or other bright enough light source) to illuminate the subcutaneous capillaries of the fingertips. When the heart pushes fresh blood into the capillaries, the brightness (depth of red) will change slightly. By monitoring this regular change interval by the camera, the heartbeat can be calculated. As a winner of Toutiao's Qingyun Plan and Baijiahao's Bai+ Plan, the 2019 Baidu Digital Author of the Year, the Baijiahao's Most Popular Author in the Technology Field, the 2019 Sogou Technology and Culture Author, and the 2021 Baijiahao Quarterly Influential Creator, he has won many awards, including the 2013 Sohu Best Industry Media Person, the 2015 China New Media Entrepreneurship Competition Beijing Third Place, the 2015 Guangmang Experience Award, the 2015 China New Media Entrepreneurship Competition Finals Third Place, and the 2018 Baidu Dynamic Annual Powerful Celebrity. |
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