图像降噪与图像增强

“Beautygate,” the latest iPhone -gate that can make images of people seem too smoothed out, is a result of two things: the . But what is digital noise reduction and why is it so important? Let’s find out.

最新的iPhone门“ Beautygate”可以使人的图像看起来过于平滑，这是两方面的结果： 。 但是什么是数字降噪，为什么如此重要呢？ 让我们找出答案。

相机传感器如何工作 (How Camera Sensors Work)

The digital sensor in your phone or camera is made from millions of small photosites. Each photosite corresponds to one pixel in the final image. When light hits a photosite, it creates an electric charge. The more light that hits the photosite, the stronger the charge created, and the brighter the pixel in the final image.

手机或相机中的数字传感器是由数百万个小的photosites制成的。 每个光点对应于最终图像中的一个像素。 当光线照射到光敏石上时，会产生电荷。 入射到光敏部位的光越多，产生的电荷越强，最终图像中的像素越亮。

As well as the charge created by light hitting the sensor, there is also a small amount of random background current that creates digital noise. This is where the problems start.

除了光线撞击传感器而产生的电荷外，还有少量的随机背景电流会产生数字噪声。 这是问题开始的地方。

Since the charge created at each photosite is , the maths works out that the brighter areas of the image have significantly more data than the shadow areas. This means the signal to noise ratio is lower in the dark areas of the image, which is why the shadow areas of an image are more prone to visible noise.

由于在每个处产生的电荷 ，数学计算得出，图像的较亮区域比阴影区域具有更多的数据。 这意味着在图像的暗区中信噪比较低，这就是为什么图像的阴影区更容易出现可见噪声的原因。

Another factor is . Larger sensors collect more light simply because they’re bigger. As a result, they’re less prone to digital noise because the signal to noise ratio is higher. Smartphone cameras—since they have such small sensors—are particularly prone to noise.

另一个因素是 。 更大的传感器会因为更大而收集更多的光。 结果，它们不易产生数字噪声，因为信噪比更高。 由于智能手机相机的传感器这么小，它们特别容易产生噪音。

将数据转换为图像 (Converting Data to Images)

When you take a photo, , your camera converts the image data into a JPG image file. It does this with some pretty complex mathematical operations that end up throwing away a lot of data to get a usable file.

拍摄照片时， ， 相机会将图像数据转换为JPG图像文件。 它通过一些非常复杂的数学运算来完成此操作，最终会丢弃大量数据以获取可用文件。

Most cameras also process the resulting image a little bit to make it look better. They do things like increase the contrast and saturation, but they also run some noise reduction algorithms. In the image below, you can see a side-by-side view of a JPEG and an unprocessed RAW file captured at the same time with my iPhone 7 Plus. Check out how much more noise is in the RAW image.

大多数相机还会对所得图像进行一点处理，以使其看起来更好。 它们执行诸如增加对比度和饱和度之类的操作，但是它们还运行一些降噪算法。 在下图中，您可以同时看到JPEG和我的iPhone 7 Plus捕获的未处理RAW文件的并排视图。 检查RAW图像中还有多少噪点。

In general, this is a good thing. Digital noise is ugly, and noise reduction algorithms are pretty well understood; they work by averaging out small variations between pixels. You can see that, especially in the highlights, in the close-ups from the images above.

总的来说，这是一件好事。 数字噪声很丑陋，并且降低噪声的算法也很容易理解。 它们通过平均像素之间的细微变化来工作。 您可以在上图的特写镜头中看到这一点，尤其是在高光部分。

For the most part, your images will look better after noise reduction is applied. It’s an important part of post-processing any digital image. The JPEG shot is undeniably a nicer image than the rough RAW. It only becomes a problem when the algorithms are too aggressive for the subject, as is the case with beautygate. When this happens, natural variations like skin tones get smoothed out as well as any digital noise. I’ve taken things way too far in the image below.

在大多数情况下，应用降噪后，图像会看起来更好。 这是对任何数字图像进行后处理的重要部分。 毫无疑问，与粗糙的RAW相比，JPEG拍摄的图像更好。 仅当算法对受试者过于激进时才成为问题，例如beautygate就是这种情况。 发生这种情况时，诸如肤色之类的自然变化以及任何数字噪声都会被消除。 我在下面的图片中做的太过分了。

And since the original data is thrown away, there’s not much you can do after the fact.

而且由于原始数据已被丢弃，因此事后您无能为力。

防止手机噪音过大 (Preventing Aggressive Noise Reduction On Your Phone)

The simplest way to prevent your phone or camera from applying overly aggressive noise reduction algorithms is to prevent them from applying any automatic noise reduction at all. To do this, you simply have to shoot in RAW.

防止手机或相机应用过分主动的降噪算法的最简单方法是完全避免自动降噪。 为此，您只需要以RAW拍摄即可。

With RAW images, all the image data—noise and everything—is stored in the file. It gives you more leeway when it comes to post-production and lets you control how much noise reduction is applied.

对于RAW图像，所有图像数据(包括噪声和所有内容)都存储在文件中。 在后期制作方面，它给了您更多的回旋余地，并让您控制应用了多少种降噪方法。

On an iPhone, you’ll . I’m . On Android, the camera app on your phone may allow you to shoot RAW; if not, . By default, your DSLR or mirrorless camera should shoot RAW images. If it’s not the default on your camera, there’ll be a setting in the menu to change the format to which images are saved.

在iPhone上，您 。 我是 。 在Android上，手机上的相机应用可能允许您拍摄RAW。 如果不是， 。 默认情况下，您的DSLR或无反光镜相机应拍摄RAW图像。 如果这不是您相机的默认设置，则菜单中会有一个设置可以更改保存图像的格式。

Noise reduction isn’t a bad thing but, when your camera or smartphone automatically applies too much, things can look weird. The best thing to do is shoot RAW and take control.

降噪并不是一件坏事，但是，当您的相机或智能手机自动应用过多时，看起来会很奇怪。 最好的办法是拍摄RAW并进行控制。

翻译自:

图像降噪与图像增强