Analysis of basic knowledge of mobile phone camera

December 30, 2023

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Pixel: What is usually called "XXX million pixels" actually refers to the resolution of the camera. Its numerical value is mainly determined by the number of pixels (i.e., the smallest photosensitive unit) in the camera sensor. For example, 5 million pixels means that there are 500 pixels in the sensor. Ten thousand pixels are the same as the number of pixels in a mobile phone screen that determines whether the screen has a resolution of 720p or 1080p.


Pixels determine photo quality?


It is generally thought that the higher the pixels of the camera, the clearer the photos taken, in fact. The only thing that the camera's pixels can determine is the resolution of the pictures it takes. The higher the resolution of the picture, it only means that the size of the picture is larger, but it does not mean that the picture is clearer.


However, the current mainstream mobile phone screens are 1080p level (1920×1080 pixels). Whether it is a 4208×3120 pixel photo taken by a 13-megapixel camera or a 3200×2400 pixel photo taken by an 8-megapixel camera, it is beyond the interpretation range of a 1080p screen. , will eventually be displayed with 1920×1080 pixels, so there is no difference in the clarity seen by the naked eye.

So what are the advantages of high pixels?


The size of the picture taken by a camera with higher pixels is larger. If we want to print the sample, based on the conventional printing standard of 300 pixels/inch, the 4208×3120 pixel sample taken by the 13-megapixel camera can print 17 inch photos, while the 3200×2400 pixel sample from an 8-megapixel camera starts to blur when printed over 13 inches. Obviously, the 13-megapixel camera sample can be printed in a larger size.


Since pixels are not the key factor in determining picture quality, who is? The answer is sensors.


There are two main types of camera sensors: CCD and CMOS. Although CCD sensors have good image quality, they are expensive and are not suitable for mobile phones. CMOS sensors are the most widely used in the field of mobile phones due to their lower power consumption, price and excellent image quality.

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CMOS sensors are divided into two types: back-illuminated and stacked. They come from the same family. The technology was first developed by Sony. Sony's back-illuminated sensor is branded "Exmor R" and the stacked sensor is "Exmor RS".


Relatively speaking, the larger the sensor size, the better the photosensitive performance, the more photons (graphic signals) it captures, the lower the signal-to-noise ratio, and the better the imaging effect. However, a larger sensor will increase the size and weight of the mobile phone. ,Increased costs.

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The emergence of the back-illuminated sensor effectively solves this problem. Under the same size, it increases the sensor's photosensitivity by 100%, effectively improving the imaging quality in low-light environments.


In August 2012, Sony released a new stacked sensor (Exmor RS CMOS). It should be noted that it is not an evolutionary relationship with the back-illuminated sensor, but a parallel relationship. The main advantage of the stacked sensor is that the number of pixels remains the same. As the situation changes, making the sensor size smaller can also be understood as, when the number of pixels is the same as that of the back-illuminated sensor, the size of the stacked sensor will be smaller, thereby saving space and making the phone thinner. , lighter.