Signal to noise ratio of photography

The landlord asked a very professional question, and I tried to answer it.

1, the quality of digital imaging (including still photos and dynamic videos, the principle is the same) is determined by the signal-to-noise ratio of the sensor. Signal-to-noise ratio is the ratio of effective component power to noise component power in photoelectric signal, and the unit is dB. The higher the signal-to-noise ratio index, the higher the purity of image quality and the higher the definition. On the contrary, the more invalid components (noise or noise), the worse the purity of image quality (including color, details, etc.). ), and the worse the definition;

2, pixels. Pixel, called pixel, refers to the basic primitive pigment and the basic coding of its gray level, and is the basic unit of digital image. There are two important concepts related to pixels: first, the resolution, that is, the accuracy of the screen image, refers to how many pixels the display needs to display the image perfectly; The second is clarity, which refers to the clarity of every detail shadow and its boundary on the image and the ability to decompose the details of the shooting scene;

3. In a sensor with the same size, the fewer the total number of pixels, the lower the pixels per inch, the larger the area of a single pixel, the more fully the light sensitivity of a single pixel, and the less noise it produces. The total noise generated by the sensor in the photoelectric conversion process is also less, the signal-to-noise ratio index is better, and the imaging quality is better. On the other hand, the higher the pixel per inch, the smaller the area of a single pixel and the lower the photosensitivity of a single pixel. Moreover, the more the total number of pixels, the more noise generated by synchronization and the worse the image quality. Of course, this is based on the same sensor technology. If the sensor technology is different, for example, high pixels adopt more advanced sensor technology (such as copper bonding technology instead of aluminum bonding technology, seamless chip technology, etc.). ), high pixels can make up for or reduce the side effects of signal-to-noise ratio decline to some extent.

4. In photography, there is a saying that the higher the pixel, the richer the details and the finer the picture quality. Actually, this is a misunderstanding.

First of all, exquisiteness is the actual reflection of definition, and whether the picture quality is exquisite or not is closely related to the display carrier. In the case of the same display carrier, there is no absolute basis that the higher the pixel, the finer it is. Take the picture quality difference between 8 million pixels and 2,654.38 million pixels as an example. Video taken by the landlord, resolution 1080 p (the same is true for photos). If viewed on a display with a resolution of 1920 x 1080p, the display of 1080 p has more than 2 million light-sensitive display points. Therefore, the 1080P display screen can only display more than 2 million pixels, and the extra pixels (no matter how many) are invisible to human eyes on the display screen. Under this premise, 8 million pixel video (or photo) and 265,438+10,000 pixel video (or photo) can only display more than 2 million pixels on the 1080P display (the extra pixels cannot be displayed and cannot be seen), and because the signal-to-noise ratio index is high when shooting 265,438+10,000 pixel video, there is less noise, but the image (picture) is not enough. If a 4K display (3840x2160) is used, the perfect display of 4K display needs more than 8 million pixels, and 8 million pixels of video or photos can meet the pixel value required by 4K display, while 265438+ 10,000 pixels can no longer support the pixel value required by 4K display. On this premise, no matter how high the quality of the 2 10 pixel image or picture is, without the necessary number of pixels, the fineness or clarity of the 8 million pixel image or picture will be higher.

Secondly, about the details. On the basis of the same sensor area, it is a fact that the higher the pixel, the richer the details captured. However, limited by the display carrier, 8 million pixels and 265,438+million pixels can display the same details on the 1080P display screen, so it is difficult to show the advantages of 8 million pixels with richer details. Only in two cases can the advantages of high pixel detail be realized. One is the display carrier with higher resolution, such as 4K, 6K or even 8K, 10K displays that may appear in the future. Second, in the case of screen shot viewing, once a part of an image or picture with 265438+ million pixels is cut off, the pixel value of the cut-off image part can no longer support the 2 million pixels required for 1080P display, while an image with 8 million pixels can still maintain the 2 million pixels required for 1080P display after being cut off. Therefore, only in the case of high-resolution display or screenshot viewing, high pixels have the advantage of imaging details;

4. As for the problem of the landlord, if you look at it on the 1080P monitor, the video with 265438+ megapixels will be clearer; If you watch it on a 4K monitor, the 8 megapixel video will be clearer.