Traditional Culture Encyclopedia - Photography and portraiture - Why is the dynamic range of human eyes much larger than that of cameras?
Why is the dynamic range of human eyes much larger than that of cameras?
The difference between harsh sunlight and starlight is 10 8, which is 100 million times. Calculate log2 10 8 = 26.6.
In the language of photography, the dynamic range of light should be in the order of 27Ev. In fact, because of the reflection and superposition of light, the dynamic range should far exceed this value.
This is the actual lighting situation.
Let me talk about the dynamic range of the camera first.
At present, there are two kinds of photosensitive elements in cameras, ccd and cmos. It can be understood that the photosensitive element is actually composed of pixels with a small area (actually called photosensitive element, its size is related to the resolution of photosensitive element, and pixels are directly used for convenience of understanding). The process of exposure is actually the process of storing light information into these pixels. The pixel's ability to store photons is limited. When it exceeds a certain value, just as a bucket will overflow when it is full, no amount of water can be wasted. At the same time, due to noise (thermal noise and statistical noise), the recorded optical information will have a lower limit.
The dynamic range of the camera is the ratio of the upper and lower limits of the recording light intensity (proportional to the stored photon quantity).
Ps, the larger the pixel area, the more photon information can be stored, and the better the anti-noise ability. Therefore, large size or low pixel will have better dynamic range or better image quality, which also explains why the image quality of 500w iphone4 is better than that of most Android 800W (of course, this is also related to software algorithms), and also explains why the image quality of Quan Huafu is better than APS-C.
Ps Say it again, in fact, I really want to buy a medium format, and I burst into tears when I mention it. .
Dynamic range of human eyes
I can't see how many cells there are in this picture. The soul is fragile! )
Take a look at our awesome human eyes. There are about 7 million pyramidal cells and 65.438+0.20 billion rod cells in human retina. Pyramid cells are responsible for strong light perception and color discrimination, while rod cells are responsible for weak light perception and can only distinguish between light and dark. Each retina can send nearly 654.38+00 megabytes of signals in one second. From this1200,000 rod cells, you should know how powerful the dynamic range of the human eye should be.
Let's make a comparison.
In fact, the photosensitive element of a camera can record a wide dynamic range, but it is called bit depth in numbers because it needs to convert photoelectric information. The higher the recording depth, the larger the recordable dynamic range. Download the relationship diagram between bit depth and dynamic range from the Internet;
Most RAW files of SLR digital cameras can record the bit depth from 10 to 14, so the theoretical dynamic range is 10- 14ev. The actual dynamic range of most digital cameras can be 5-9EV.
So dear children's shoes, the camera can shoot Raw, so be sure to shoot raw!
The dynamic range of the camera is a function of the ISO value. The higher the ISO value, the more serious the noise and the lower the dynamic range.
The human eye, on the other hand, is not static, and its function is more like a camera than a static camera. People's eyes rotate repeatedly, constantly receiving external light signals, and "updating" the image details in the brain at any time. At the same time, the brain can combine different signals obtained by both eyes, which can also increase the resolution of the image. In addition, we often turn our eyes or necks to receive more information. Therefore, the organic combination of eyeball and brain makes the resolution of human eyes not only determined by photoreceptors on iris.
Moreover, the dynamic range of human eyes can be changed because of the change of sensitivity, but the ability of human eyes to adjust sensitivity is a bit slow, and it takes time to change, which is why it feels dark when going out at night, but it will be fine after a while.
However, the sensitivity of the human eye is not afraid of the influence of noise (some studies say that the human eye also produces noise, so I didn't see it, haha), and the human eye also has a powerful post-tool, that is, the brain. What you usually see are brain-filled images, so what do you say? If the camera is late, it will have to be dragged into the ps.
PS: Reprint the answer on Zhihu.
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