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They’re there, lurking in your image files. But have you ever wondered what are image channels are? And what do they have to do with RGB and CMYK? Here’s the answer.

它们在那里，潜伏在您的图像文件中。 但是您是否想知道图像通道是什么？ 它们与RGB和CMYK有什么关系？ 这就是答案。

The channels panel in Photoshop is one of the most disused and misunderstood parts of the program. But images have color channels with or without Photoshop. Read on to find out what color channels are, what RGB and CMYK are, and learn a little bit more about how image files work.

Photoshop中的“通道”面板是该程序中最不常用和误解的部分之一。 但是，无论是否使用Photoshop，图像都有色彩通道。 继续阅读以了解什么是色彩通道，什么是RGB和CMYK，并进一步了解图像文件的工作方式。

光和印刷的原色 (Primary Colors of Light and Print)

“Primary Colors,” at least in the sense you might have learned of them in High School art class, refer to a set of pigments that can be combined in various ratios to create every color in the visible spectrum. RGB and CMYK are combinations of a different set of primary colors: the primary colors of light, and primary colors for printing. Let’s briefly look at both of these, and contrast the two of them.

至少在高中美术课上您可能已经了解到它们的意义上，“原色”是指可以以各种比例组合以在可见光谱中产生每种颜色的一组颜料。 RGB和CMYK是不同原色集的组合：光的原色和打印的原色。 让我们简要地看一下这两个，并对比一下两个。

It’s a well documented property of light that it can be refracted into the various, slower wavelengths that make it up. Another observable property of light is that it can also be recombined from these various wavelengths (we call them colors) back into pure white light. Issac Newton documented this in Opticks, a book on his studies of light and the refraction of it.

充分记录下来的光的特性是，它可以折射成组成它的各种较慢的波长。 光的另一个可观察到的特性是，它也可以从这些各种波长(我们称为颜色)重组为纯白光。 伊萨克·牛顿(Issac Newton)在《 Opticks 》一书中对此进行了记录，该书是他对光及其折射的研究。

The RGB color model is exactly this. Combining light from Red, Green, and Blue sources, pure white light (or the illusion of it) can be achieved on computer screens or on various kinds of television monitors. The RGB model of image is simply a way for images to track the amount of Red, Green and Blue light each pixel has. More on how, later, but first, let’s compare this light-based model to how print processes work.

RGB颜色模型就是这样。 组合来自红色，绿色和蓝色光源的光，可以在计算机屏幕或各种电视监视器上获得纯白光(或其错觉)。 图像的RGB模型只是图像跟踪每个像素具有的红色，绿色和蓝色光量的简单方法。 接下来，但首先，让我们更多地将基于光的模型与打印过程的工作方式进行比较。

青色，洋红色，黄色，键线 (Cyan, Magenta, Yellow, Keyline)

You’re possibly only familiar with the colors listed above because you buy CMYK cartridges for your desktop printer. Cyan, Magenta, and Yellow are called the “process colors” of printing, and can be thought of as a primary set of inks. You can see from the illustration above, that they combine in various amounts to create a wide range of colors, including a mixed black.

您可能只熟悉上面列出的颜色，因为您购买了台式打印机的CMYK墨盒。 青色，品红色和黄色被称为印刷的“原色”，可以被认为是主要的油墨组。 您可以从上图中看到，它们以各种数量组合在一起以创建各种颜色，包括混合黑色。

Because mixing huge quantities of three inks can become expensive, printers decided to add black as a fourth color to this set. Black ink (known as key, or keyline, hence the “K” in “CMYK”) allows for less waste of the other three primary color, as well as richer prints with more color depth.

由于混合大量的三种墨水可能会变得昂贵，因此打印机决定将黑色作为第四种颜色添加。 黑色墨水(称为键或键线，因此称为“ CMYK”中的“ K”)可以减少对其他三种原色的浪费，并可以打印出更丰富的色深。

我们真的需要两者吗？ (Do We Really Need Both?)

CMYK files may be all well and good for printers, but why can’t we just pick one and use only it? As you might have guessed, RGB and CMYK files each are used to solve their own individual problems.

CMYK文件对于打印机来说可能很好，但是为什么我们不能仅选择一个文件并仅使用它呢？ 您可能已经猜到了，RGB和CMYK文件分别用于解决自己的问题。

RGB files work with a model that is based around light. Because of this, they are ideal image file formats for on-screen and web based design—formats that will only be viewed through light projecting monitors or televisions.

RGB文件可用于基于光的模型。 因此，它们是用于屏幕和基于Web的设计的理想图像文件格式，这些格式只能通过投光显示器或电视观看。

CMYK is the preferred color model when working directly for four color process print. It is possible for a designer to work in RGB files, but it doesn’t make sense to work with colors that can’t be printed. Therefore, working with CMYK can help eliminate the color shifts and various problems when translating an RGB document to a printed CMYK color gamut.

直接用于四色印刷时，CMYK是首选的颜色模型。 设计人员可以使用RGB文件，但是使用无法打印的颜色没有意义。 因此，在将RGB文档转换为打印的CMYK色域时，使用CMYK可以帮助消除色偏和各种问题。

这与图像通道有什么关系？ (What Does All This Have to Do with Image Channels?)

The illustration above shows Photoshop’s color picker tool. In a common 24 bit RGB image file, images are essentially made of three smaller 8 bit files. These smaller files are the image’s channels, and they have a range of 256 values, ranging from 0 – 255. You can see evidence of this in your color picker, with values broken down between Red, Green, and Blue on the left, and Cyan, Magenta, Yellow, and Keyline (black) on the right.

上图显示了Photoshop的颜色选择器工具。 在常见的24位RGB图像文件中，图像本质上是由三个较小的8位文件组成。 这些较小的文件是图像的通道，它们的范围是256个值，范围从0到255。您可以在颜色选择器中看到这一点的证据，其值在左侧的红色，绿色和蓝色之间分解，并且右侧为青色，品红色，黄色和关键线(黑色)。

Each channel represents the amount of light (RGB) or simulated ink (CMYK) each isolated color needs to combine to create the digital image. You’ll notice, that in the RGB file illustrated above, the brightest bulbs in the corresponding channels (marked Red, Green, and Blue) are the ones for the corresponding channel. In other words, the green bulb is the brightest in the green channel because it takes more bright green light to create an image of a glowing green bulb.

每个通道代表每种孤立的颜色需要组合以创建数字图像所需的光量(RGB)或模拟墨水(CMYK)。 您会注意到，在上述的RGB文件中，相应通道(标记为Red，Green和Blue)中最亮的灯泡就是相应通道的灯泡。 换句话说，绿色灯泡是绿色通道中最亮的灯泡，因为它需要更亮的绿色光才能创建发光的绿色灯泡的图像。

Those combinations of single color, 256 color images combine color information to create millions of color tints, hues, and shades in every garden variety RGB JPG or CMYK Photoshop file.

单色256色图像的这些组合结合了颜色信息，从而在每个花园品种RGB JPG或CMYK Photoshop文件中创建了数百万种颜色，色调和阴影。

等待，什么是Alpha通道？ (Wait, What Are Alpha Channels?)

Simply to make things one step more confusing, some image files (notably, like PNG) contain more image information in an extra channel. This channel is essentially no different than an RGB or CMYK channel, with 256 shades of gray representing the image areas. However, Alpha channels have on crucial difference: they denote transparency, not color information.

只是为了使事情变得更加混乱，某些图像文件(尤其是PNG)在一个额外的通道中包含更多图像信息。 该通道与RGB或CMYK通道基本没有区别，其中256个灰色阴影表示图像区域。 但是，Alpha通道具有至关重要的区别：它们表示透明度，而不是颜色信息。

The image illustrated above shows the composite RGB image on the left, with information from the alpha channel shown on the right. Wherever there is white, the image is opaque. Where there is black, it is perfectly clear, like a transparent PNG. The shades of gray in between allow for transparency beyond a simple “on” and “off” switch.

上图所示的图像在左侧显示了合成RGB图像，在右侧显示了来自alpha通道的信息。 无论哪里有白色，图像都是不透明的。 黑色的地方非常清晰，就像透明的PNG。 介于两者之间的灰色阴影使透明性超出了简单的“开”和“关”开关。

Nothing else changes with an Alpha channel. It is more or less identical to any other 8-bit channel in any image, and is more or less just as easy (or as hard) to understand.

Alpha通道没有其他改变。 它或多或少与任何图像中的任何其他8位通道相同，并且或多或少的易于理解(或难以理解)。

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Have questions or comments concerning Graphics, Photos, Filetypes, or Photoshop? Send your questions to

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对图形，照片，文件类型或Photoshop有疑问或意见吗？ 将您的问题发送到ericgoodnight@howtogeek.com, and they may be featured in a future How-To Geek Graphics article. ericgoodnight@howtogeek.com ，它们可能会在以后的How-To Geek Graphics文章中介绍。

Image Credits: Prism Reflections by sburke2478. Red Eyed Tree Frog by Carey James Balboa. Led 1 by Alessandro Vannucci. CMYK Process Ink by w_lebelie.

图片来源： sburke2478的棱镜反射。 凯里•詹姆斯•巴尔博亚着“红眼树蛙” 。 由亚历山德罗·范努奇( Alessandro Vannucci)领导。 w_lebelie的CMYK处理油墨。

翻译自: https://www.howtogeek.com/howto/42393/rgb-cmyk-alpha-what-are-image-channels-and-what-do-they-mean/

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