Why is a surveillance camera with 3 million pixels better than a mobile phone with tens of millions of pixels?

1. The core hardware of digital imaging is three items, one is lens, the other is sensor, and the third is image processor. Among them, the sensor is related to the pixel;

2. The sensor is the most important core component of digital imaging, and its function is to convert different light intensities obtained by the lens into corresponding charge signals, and then the image processor converts the charge signals into electronic documents visible to human eyes. Pixels (also called photodiodes) are the components of the sensor responsible for photoelectric conversion, and many pixels are evenly distributed on the plane (also curved) of the sensor;

3. the quality of converting light intensity into charge signal by pixels involves two technologies, one is ADC (analog-to-digital conversion) technology, and the other is SNR (signal-to-noise ratio) technology. Among them, ADC involves pixel array, lead material, amplifier technology, data refresh process and so on. The ADC of the same sensor in the same era is basically the same. Assuming the ADC technology is the same, it is SNR； that determines the imaging quality;

4. SNR is the ratio of effective signal to ineffective noise. The higher the signal-to-noise ratio, the less noise, the higher the quality of the charge signal converted by the amplifier, and the better the image quality converted by the same technology processor. When the ADC is the same, it is pixels per inch who determines the SNR;

5. pixels per inch is the ratio of the total number of pixels to the sensor area. The lower the pixels per inch, the larger the area of a single pixel (the area of a single pixel is variable, not fixed), the greater the ability to capture light intensity, and the higher the quality of the converted charge signal. Assuming that the sensor area is the same (different sensor areas can be converted), the density of 3 million pixels is much lower than that of tens of millions of pixels, and the area of a single pixel is larger, the photosensitive performance is stronger and the image quality is higher;

6. Under the same ADC, the lower the pixels per inch, the better the imaging quality. However, the pixels per inch cannot be infinitely low, and the number of pixels must meet the demand for the total number of pixels. For example, a 18P display needs more than 2 million pixels, a 4K display needs more than 8.3 million pixels, and an 8K display needs 33 million pixels. Below the number of pixels required to use the carrier, the image quality will also decline; If the number of pixels is higher than the number of pixels required to use the carrier, it will be displayed and cannot be seen by human eyes;

7. Assuming that the lens quality is the same and the image processor technology is the same, the sensor with low pixels per inch has high charge signal quality and clearer image within the range of meeting the requirements of using carriers. The pixels per inch of a 3 megapixel camera is low, the area of a single pixel is large, the sensitivity of a single pixel is strong, and the quality of the generated charge signal is high, and the definition is higher than that of a mobile phone with tens of millions of pixels.