I remember that when the mobile phone first had a camera, I was very excited because at that time, I never thought about the fact that the mobile phone could take pictures. Until now, the pixels of the mobile phone camera are getting higher and higher, and the image quality is getting better and better. Some even added optical anti shake and optical zoom like SLR cameras, What are the structures of that small camera?

Camera sensor

As we all know, the most important part of determining the imaging quality of mobile phones or cameras belongs to the photosensitive elements. There are two kinds of photosensitive elements, one is CCD sensor, the other is CMOS sensor.

Among them, CCD imaging quality is good, but the manufacturing process is complex, the number of manufacturers that can produce is relatively small, the price is relatively high (thin materials are expensive), and the power consumption is also high, so it is not suitable for use on mobile devices.

The CMOS sensor consumes less power, but its image quality is not as good as that of CCD. However, with the improvement of technology, the image quality of COMS has gradually caught up with that of CCD. In addition, under the same resolution, the price of CMOS is cheaper than that of CCD. Therefore, the current mobile phone cameras in the market use CMOS sensors.

Generally, CMOS sensors can be divided into backlight CMOS sensors and stack CMOS sensors.

The so-called back illuminated CMOS sensor is actually opposite to the traditional positive illuminated CMOS sensor. Simply put, the photodiode and the wiring layer are exchanged (as shown in the figure above), so that the light first enters the photodiode, thus increasing the sensitivity and significantly improving the shooting effect under low light conditions. The iPhone 4/4S, Xiaomi 2S, Meizu MX2, and Sony LT26i are all equipped with such sensors.

The stack type CMOS sensor is a derivative of the backlight type CMOS sensor. It is the most widely used and advanced type of mobile phone camera, and belongs to Sony's exclusive technology.

The stacked CMOS sensor uses a chip with a signal processing circuit to replace the original supporting substrate of the back lit CMOS image sensor, and forms the pixel part of the back lit CMOS element on the chip by overlapping (the above figure: ①+②=③), thus realizing the process of forming a large number of pixel points on a small 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, I want to say that the photosensitive element is only an integral part of the mobile phone camera, but not a decisive factor in the imaging quality of a mobile phone, which also includes the manufacturer's optimization and adjustment of hardware through software to make it feel the best (this involves different people's feelings, which depends on the manufacturer's positioning of the product), This is also one of the decisive factors for the biggest difference in the effect of mobile phone camera quality among manufacturers,

The following are some common questions about mobile phone cameras.

Why is the camera lens round? The light sensor inside is square.

On the one hand, the circle can achieve the maximum imaging area; On the other hand, it has many optical advantages, for example, the round side can reduce the reflection of light; Moreover, the round lens is easy to grind, the assembly can be more accurate, and it is also easy to make various fine adjustments.

The most important thing is also in the mechanical structure: including the fine adjustment of focusing and zoom, it is naturally the most convenient to use spiral propulsion, and the rotation of the circular lens will not lead to the loss of imaging (if it is a rectangular lens, then turn it 90 °, and the 3 * 2 rectangular photos will be cut into 2 * 2 squares), which facilitates the setting of various adjustment mechanisms.

Lenses with medium and large frames need to be matched with films/light-sensitive elements of different sizes. It is also the most economical way to maximize the nature and materials as far as possible (special-shaped lenses, such as eyeglasses, are actually cut from round lenses. For lenses, cutting out is not helpful for imaging, but changing a negative may not be enough for the imaging range, which is typical thankless) 。

What is the principle of the application of putting your finger in front of the camera and flash of your mobile phone to detect your heart rate?

Highlight (LED flash light beside the camera, or other light sources that are bright enough) to illuminate the subcutaneous capillaries at the fingertips. When the heart presses fresh blood into the capillaries, the brightness (red depth) will change slightly. The heartbeat can be calculated by monitoring this regularly changing interval through the camera.