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can someone tell me, why videos (taken in low light place) has noise (or i dont know what to call that, the pixels playing/blinking continuously) , for example:

My questions are:

1) Why that noise is added at all? why cant the image could be static, i mean, where is black color, there should be black without noise... (same for other colors...) why colors are not static and why this annoying noise is added?

2) is there any method in photocameras (mobile, CANON etc..) , to force camera to record without noise (like professional videocameras do)?

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The noise in dim-lit environments is a result of how digital cameras work. The exposure of a picture or video depends on three essential parameters: lens aperture, shutter speed and ISO. The first two are about how much light falls on the camera sensor. The larger the aperture, the more light can enter the camera. The slower the shutter speed (i.e. the longer the exposure), the more light can enter the camera. ISO/gain is a digital amplification of the digitalised sensor signal By amplifying the signal, the camera can essentially make it brighter. However, the noise that is captured is also amplified.

What's important to understand is that if you were to expose a light and a dark scene using the same aperture, shutter speed and ISO, the dark one wouldn't have more noise than the light one, it would just be darker. The noise is a result of the camera increasing the ISO/gain to achieve a well-exposed scene (which for the camera means a normally distributed histogram).

1) Why that noise is added at all? why cant the image could be static, i mean, where is black color, there should be black without noise... (same for other colors...) why colors are not static and why this annoying noise is added?

What probably happened with your example video is that the camera noticed a dim-light environment and cranked up the ISO/gain to achieve a well-exposed video. This inadvertently increases the noise of the video as well. What you can do to circumvent this is to switch to a manual exposure mode where you set the aperture, shutter speed and ISO manually. This way, you can set your camera to underexpose the image. It will turn out rather dark, but less noisy. Keep in mind though that this does not mean you should just underexpose your video and just turn up the brightness in post-editing. This will once again increase the visible noise, because it's basically the same thing as increasing the ISO, only less efficient. So there's a tradeoff between noise and exposure as well.

2) is there any method in photocameras (mobile, CANON etc..) , to force camera to record without noise (like professional videocameras do)?

High-quality lenses will usually be faster, meaning their minimum f-number (maximum aperture) will be lower. A larger aperture means more light entering the camera in the same amount of time, so with a larger aperture you will get a brighter image than with a smaller one (while shutter speed and ISO stay the same).

High-quality cameras will usually have slightly better low-light performance, meaning there will be less noise under the same circumstances with the same settings, but that difference is rather negligible in scenes as dark as the one in your video.

You can also use a tripod to steady your camera, allowing for slower shutter speed (meaning each individual frame of your video will be exposed for a longer time). However, the shutter speed can't be slower than the inverse of the framerate for obvious reasons, so that will only do so much to brighten up your scene.

What you really need to do to lower the noise is bring in more light. You can still darken the video in post-editing, but if you are able to shoot a well-exposed video with a low-ish ISO value (the meaning of low in this context depends on your camera model), the resultant video won't have much noise regardless of how you decide to edit it. Alternatively, if you want an underexposed video (if that is the style you're going for), you can just set your camera to manual and purposefully underexpose the scene as described above.

  • excellent answer... for example, 1) ....just turn up the brightness in post-editing -- did i misunderstood that? because, lets say, if raw image if complete black, if i make it brighter in video-editor, then it will make it brighter without noise... i.e. i.imgur.com/M0EHWPB.png 2) the problem is that my JVC videocamera captures without noise, but with Canon Photocamera (SX50, video-record mode) in same brightness, has about 3-4 times more noise.. – T.Todua Apr 23 '17 at 17:12
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    @T.Todua First, you are probably not capturing RAW video unless you are using a production-grade camera. But regardless of that, the video will never be completely black even in the areas that appear to be black on the screen. The noise is a result of the analog to digital conversion and influenced by a couple of variables (including sensor size, as explained in LetTheWritersWrite's answer, forgot to mention that in my own post), brightening it up will just increase it. TBC – MoritzLost Apr 23 '17 at 17:18
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    I supposed if you underexpose hard enough, the video will eventually turn out completely black, but then there's no information to recover in post ... – MoritzLost Apr 23 '17 at 17:19
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When you have a camera with a small sensor, the little photosites can't read light very well. Photosites are like little pixels that are buckets of light that build up the image. When your sensor can't read light very well, it has to kind of guess what the light is and you just get random pixels firing off, creating that noisy pattern.

And to get rid of noise, you have to adjust the dark values with a curves or levels effect. You will crush the black levels and essentially eliminate the noise in the dark regions of your video. This is the only way to film high contrast, dark shadow images. Now, if your whole image was underexposed, then it's not as salvageable because your whole image is in the noisy threshold and will get affected by your effect right along all the other noisy parts you are trying to eliminate.

Conclusion, you can avoid this in the future by using plenty of light, a bigger sensor, or a faster lens.

Here's a great article by a talented cinematographer http://www.thehurlblog.com/film-education-testing-your-cameras-emulsion/

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