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This tutorial shares the knowledge of noise, which is a disturbing element that should not have appeared in a photo. Too much noise is likely to destroy a photo. The noise of a digital camera is mainly the rough part of the image produced by the photosensitive element when processing the light signal, and it also refers to the foreign pixels that should not appear in the image, which are often caused by electronic interference, so that the image looks like it is covered with small rough particles or color dots.

Although all the noises are noises, they can also be divided into several categories. Their causes are different and the appearance of the noises is also different. Only by understanding these, can we take better pictures and have evidence to rely on when reducing noise.

The reason for the formation of noise is that the imaging principle of the digital camera inevitably leads to noise in the photograph. when the light is sufficient, the effective light signal accounts for a higher proportion, and the noise is almost invisible. in the dark light environment, the signal-to-noise ratio decreases and the noise appears.

In general, the sensitivity of the camera is a fixed value, increasing the camera's iso is actually forcibly magnifying the original electronic signal, and the high sensitivity noise will also be amplified, resulting in a decrease in signal-to-noise ratio and an increase in noise.

In slow-door photography, when the shutter time is as long as dozens of seconds, the camera CMOS temperature increases, and long exposure will also produce noise, but the position of this noise is often fixed.

From the point of view of position, the classification of noise can be divided into random noise and fixed noise, random noise will appear in any position, fixed noise is generally produced by long exposure, and the position is also fixed.

From the color point of view, it can be divided into lightness noise and color noise, lightness noise is gray particles, color noise is often red and green small dots. Two kinds of noise will reduce the clarity of the photo and interfere with the color purity.

The first common noise reduction method is in-machine noise reduction, turn on the camera's "high iso noise reduction" and "long exposure noise reduction" switch, after taking a picture, the camera will take a certain amount of time to deal with noise reduction, which is more time-consuming, so few photographers use these two functions.

The second is ps noise reduction, such as the "details" panel in ACR / LR, which provides noise reduction function for brightness noise and color noise respectively; the "noise reduction" function in ps filter is also very similar, which can reduce noise for brightness noise and color noise respectively. Details can also be restored when noise is reduced.

The third is the plug-in noise reduction, some plug-in photography plug-ins, can be installed in the ps plug-in filter, use them to reduce noise. Nik Dfine, Noiseware and Topaz Denoise are all good noise reduction plug-ins, and the interface provides more elaborate manual options.

The fourth is dark field noise reduction, which is commonly used in starry photography with long exposure and fixed noise. Keep the parameters unchanged, cover the lens cap and take a picture, you will get a pure black picture with only noise, and then use the "subtract" mixed mode.

The fifth is stack noise reduction, in which multiple photos are taken in the early stage, and lossless noise reduction is carried out in the later stage, which is only suitable for random noise. You can read this article on the official account: too much noise? Ps stack noise reduction tutorials and principles, photographers are using lossless noise reduction skills!

Sharpening and softening noise reduction and sharpening complement each other, noise reduction and noise reduction is bound to lose details. Sharpening can deepen the details of the photo.

In ps's noise reduction tools, there are often options to preserve details. For example, in the ACR details panel, the "details" slider is used to recover details lost by noise reduction, and swiping to the right can restore more details. "contrast" can retain the contrast of the photo, when the value is 0, as long as there is a light and shade change between two pixels, ACR will regard this as noise and noise reduction. When the slider is 100, the contrast between the two pixels is not considered noise, so there is no noise reduction at all.

This article is from the official account of Wechat: photography Research Society (ID:shoujiPhotography), by Zhang Xiaozhang.

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