什么是Photoshop中的曲线？
The Curves adjustment layer is one of the most important tools in Photoshop. It’s the best way to adjust the brightness and contrast of your images. If you want to get good with Photoshop, you’ll need to master Curves.
曲线调整层是Photoshop中最重要的工具之一。 这是调整图像亮度和对比度的最佳方法。 如果您想与Photoshop结合使用，则需要掌握Curves。
If you aren’t familiar with adjustment layers, you’ll want to learn about them before reading this article. So check out our guides to layers and adjustment layers before continuing–and if you’re new to Photoshop, you should also check out our 8-part beginner’s guide before continuing.
如果您不熟悉调整层，那么在阅读本文之前，您需要了解它们。 因此，在继续之前，请查看有关图层和调整图层的 指南 -如果您不熟悉Photoshop，还应在继续之前查看我们的8部分入门指南 。
一切都始于直方图 (It All Starts with the Histogram)
A histogram is a graph of all the tones in your image. Every pixel in a digital photograph has a Luminosity value (that’s how bright it is) of somewhere between 0 (pure black) and 255 (pure white).
直方图是图像中所有色调的图形。 数码照片中的每个像素的亮度值(即亮度)在0(纯黑色)到255(纯白色)之间。
The histogram graphs how many pixels of each luminosity there are in the image. In the histogram in the image below, you can see there are a lot more pixels with low luminosities (darker colors) than pixels with high luminosities (brighter colors). A quick glance at the actual image confirms it.
直方图绘制图像中每个亮度的像素数。 在下图中的直方图中，您可以看到亮度较低(较暗的颜色)的像素比亮度较高(较亮的颜色)的像素更多。 快速浏览一下实际图像即可确认。
Histograms are really useful tools for photographers, and anyone else working in Photoshop, because they show you information that’s hard to see directly with your eyes. From a printer’s perspective, there’s a big difference between something that’s almost black and something that’s actually black, but it’s really difficult to tell the difference just by eyeballing it.
直方图对于摄影师和其他在Photoshop中工作的人来说确实是非常有用的工具，因为直方图会向您显示难以直接用眼睛看到的信息。 从打印机的角度看，几乎是黑色的东西和实际上是黑色的东西之间有很大的区别，但是仅通过目视辨别是很难的。
For a more detailed take on histograms and how you can make them better, check out our guide on the subject.
有关直方图的更多详细信息以及如何使直方图更好的方法，请查看有关此主题的指南 。
曲线调整层 (The Curves Adjustment Layer)
The Curves adjustment layer is a tool for directly manipulating the histogram. Rather than let Photoshop’s algorithms determine how different areas of your image get brightened, you can go in and do everything yourself. Curves are a little trickier to use than a simple slider, but the extra control is worth the complexity.
曲线调整层是直接处理直方图的工具。 您可以自己进行所有操作，而不必让Photoshop的算法确定图像的不同区域如何变亮。 曲线比简单的滑块要难一些，但是额外的控制值得复杂性。
Let’s take a close look at a Curves adjustment layer. You’ve got the histogram, but on top of that you’ve got a line sloped at 45 degrees. This is another kind of graph: an Input/Output chart.
让我们仔细看一下“曲线”调整层。 您已经有了直方图，但最重要的是，您有一条倾斜45度的线。 这是另一种图形：输入/输出图表。
The line in a Curves adjustment shows the relationship between the Input and Output for every luminosity value. Input is on the X-axis and Output is on the Y-axis.
曲线调整中的线显示每个亮度值的输入和输出之间的关系。 输入在X轴上，输出在Y轴上。
While the line is at 45 degrees, every Input value is mapped to the exact same Output value. All the pixels with a luminosity of 100 stay at 100 after you’ve applied the Curves layer.
直线处于45度时，每个输入值都映射到完全相同的输出值。 应用“曲线”图层后，所有亮度为100的像素均保持为100。
When you change the slope of the line, you change the relationship between the Input and Output values. If you add a point at an Input of 100 and drag it down to an Output of 80, all the pixels that had a luminosity of 100 will now have a luminosity of 80. If you compare the image below to the one above, you’ll see it’s darker.
更改直线的斜率时，将更改输入和输出值之间的关系。 如果您在输入100处添加一个点并将其向下拖动到输出80，则所有亮度为100的像素现在的亮度将为80。如果将下面的图像与上面的图像进行比较，您将会看到它更暗。
Photoshop’s Curves aren’t a blunt tool, though. If you just changed the luminosity of all the pixels with a value of 100 while ignoring the pixels with a value of 99 or 101, your image would look ridiculous. Instead, the Curves tool changes the Input/Output ratio of all the nearby pixels changes as well. Pixels with a value of 99 will probably be mapped to 79, while pixels with a value of 101 will get mapped to 81. Pixels with a value of 110, will get mapped to around 87 and so on until the curve of the slope smooths out. That’s why the image still looks natural.
不过，Photoshop的“曲线”并不是一个钝器。 如果您只是更改了所有值为100的像素的亮度，而忽略了值为99或101的像素，则图像将看起来很可笑。 取而代之的是，“曲线”工具也会更改所有附近像素的输入/输出比率。 值99的像素可能会映射到79，而值101的像素将映射到81。值110的像素将映射到87左右，依此类推，直到斜率曲线平滑为止。 这就是为什么图像看起来仍然很自然的原因。
使用曲线层 (Using a Curves Layer)
Now that you have some idea of how Curves work in theory, let’s look at it in action. We’ll take the same image, and apply eight different curves to show you how it affects the photo.
现在您已经知道了Curves在理论上是如何工作的，让我们看看它在实际中的作用。 我们将拍摄同一张图片，并应用8条不同的曲线，向您展示它如何影响照片。
This Curve brightens the pixels with middle luminosity values.
该曲线使亮度值中等的像素变亮。
This Curve darkens the pixels with middle luminosity values.
该曲线使具有中等亮度值的像素变暗。
This Curve brightens the pixels with dark luminosity values.
此曲线使用暗亮度值加亮像素。
This Curve darkens the pixels with dark luminosity values.
该曲线使具有暗亮度值的像素变暗。
This Curve brightens the pixels with bright luminosity values.
该曲线以明亮的亮度值使像素变亮。
This Curve darkens the pixels with bright luminosity values.
该曲线使亮度值明亮的像素变暗。
This Curve darkens the dark pixels and brightens the light pixels to add contrast.
该曲线使暗像素变暗，使亮像素变亮以增加对比度。
This Curve adds contrast, just a lot more of it.
该曲线增加了对比度，但对比度却高得多。
As you can see with all the examples above, Curves layers give you a huge amount of flexibility in how you adjust the brightness of all the different pixels in your image.
正如您在上面的所有示例中看到的那样，“曲线”图层为您提供了极大的灵活性，可用于调整图像中所有不同像素的亮度。
颜色和曲线 (Colors and Curves)
As well as a luminosity value, every pixel in a color image has a Red, a Blue, and a Green value that lies somewhere between 0 and 255. These values determine its color.
除了亮度值外，彩色图像中的每个像素都具有介于0到255之间的红色，蓝色和绿色值。这些值确定其颜色。
Each color has its own histogram that represents the number of pixels with that specific color value. Like with the luminosity histogram, a Curves layer can be used to manipulate it.
每种颜色都有其自己的直方图，该直方图代表具有该特定颜色值的像素数。 像发光度直方图一样，可以使用“曲线”层对其进行操作。
To use a Curves layer to modify the color in an image, add one and click on the dropdown where it says RGB.
要使用“曲线”层修改图像中的颜色，请添加一个，然后单击显示为RGB的下拉菜单。
Select the color you want to edit and you’ll see the relevant histogram.
选择要编辑的颜色，您将看到相关的直方图。
When you edit a color using a Curves layer, you affect every pixel with that color in it. Dragging up on the Red Curve increases the intensity of the reds in the image.
使用“曲线”图层编辑颜色时，会影响其中包含该颜色的每个像素。 在红色曲线上向上拖动可增加图像中红色的强度。
Dragging down on the Red Curve decreases the intensity of the reds and thus increases the apparent intensity of its complimentary color, cyan.
在红色曲线上向下拖动会降低红色的强度，因此会增加其互补色青色的表观强度。
(Green’s complimentary color is magenta, and blue’s is yellow.)
(绿色的互补色是洋红色，蓝色的是黄色。)
You can combine all four Curves in a single adjustment layer to create different effects. Below you can see an image where I’ve increased the Blue Curve, decreased the Green and Red Curves, and brightened everything with the RGB Curve.
您可以将所有四个曲线合并在一个调整层中以创建不同的效果。 在下面，您可以看到图像，其中我增加了蓝色曲线，减少了绿色和红色曲线，并使用RGB曲线使所有内容变亮。
Color curves are an advanced technique and probably not something you need to focus on when you’re just starting out. As you get more skilled with Photoshop, you’ll start to encounter situations where being able to manipulate each color histogram individually becomes important. They can be used to do everything from fix color problems to creatively color tone your images.
颜色曲线是一种高级技术，刚入门时可能不需要关注。 随着您对Photoshop的熟练掌握，您将开始遇到以下情况：能够分别操纵每个颜色直方图变得很重要。 它们可以用于解决所有问题，从解决颜色问题到创造性地为图像设置色调。
The Curves adjustment layer is the most powerful way to adjust the brightness and contrast of your images. It gives you total control over how every tone is rendered. Knowing how to use Curves is crucial for anyone who wants to use get the most out of Photoshop.
曲线调整层是调整图像亮度和对比度的最强大方法。 它使您可以完全控制每种音调的呈现方式。 对于想使用曲线的人来说，充分利用Photoshop至关重要。
翻译自: https://www.howtogeek.com/276247/what-are-curves-in-photoshop/