What is a color gamut

https://epxx.co/artigos/gamut_en.html

COLOR GAMUT IS THE COLOR PALLETE THAT A GIVEN TECHNOLOGY OR PROCESS IS CAPABLE OF REPRODUCING. A fact unknown by the layman is that every technology (color TV, color printer, etc.) has severe limitations in color reproduction.

色域是一种特定的技术或者过程有能力重现的颜色版。外行不知道的一个事实是,每种技术(彩色电视,彩色打印机等)在色彩再现方面都有严重的局限性。

That’s why we can discriminate between natural and artificial images at a glance — e.g. what you see through an open window versus a picture or a TV screen mounted in the window’s frame. And we can tell apart an analog TV, a digital TV, a printed picture, etc. because every media has a different ‘look’ regardless of resolution.

这就是为什么我们可以一目了然地区分自然和人工图像 —— 例如,你通过一个打开的窗户看到的景象和挂在窗户上的电视屏幕或者一幅画。同时,我们可以区分模拟电视,数字电视,一张打印图片,等等,因为每种媒体都有不同的“look”,无论分辨率是多少。

In order to understand gamut, it is important to understand the CIE diagram (Figure 1). It is the result of extensive research about human vision. It is also known as the “horseshoe diagram”, and its funny shape will be explained soon.

为了理解色域,理解 CIE 图很重要(图 1)。这是对人类视觉广泛研究的结果。它也被称为“马蹄图”,它有趣的形状将很快被解释。

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Figure 1: CIE diagram (Source: Wikipedia)

The upper curve delimiting the shape, that resembles a horseshoe, is related to pure colors — the ones we can see in a rainbow. The colors spot-on this curve are the only ones that actually exist in nature. The blue numbers are the wavelengths of each color. For example, red has a wavelength of 620nm or 0.000620mm. For comparision, a microwave radio signal has wavelengths between 30cm and 3mm.

限定这个形状的上曲线,类似马蹄的那条,和纯色相关 —— 我们可以在彩虹中看到的那些。这条曲线上面的颜色,是自然界中实际存在的仅有的颜色。蓝色的数字是每种颜色的波长。例如,红色有 620ns 或者 0.000620mm 的波长。作为对比,微波无线电有 30cm 到 3mm 之间的波长。

Only lasers can generate the pure colors at the borders of the diagram. Mundane technologies always add small amounts of other colors. This limitation has important consequences, as we will see. In particular the violets (bottom left corner) are very difficult to generate in the purest form.

只有激光可以生成这张图边界上的纯色。平常的技术总是添加少量的其他颜色。这个限制有严重的后果,我们稍后将会看到。特别是紫罗兰色(左下角)非常难以生成纯净的样子。

The bottom edge of the diagram, a straight line, is called the “magenta line”. These colors between violet and red are not rainbow colors. When our eyes are stimulated by a mixture of blue and red, or violet and red, then we “see” colors like purple, magenta or pink.

图的底部边缘,是一条直线,被称作“品红线”。这些介于紫罗兰色和红色之间的颜色不是彩虹色。当我们的眼睛被混合的蓝色和红色,或者紫罗兰色和红色刺激到,我们会“看到”像紫色,品红或者粉红的颜色。

The colors in the bulk of CIE diagram are “less pure” than colors at the edges. Near the center, the colors are very pastel. The white color has its spot in the center, since white is a perfectly balanced mix of all rainbow colors.

CIE 图主体的颜色比边缘的颜色 “less pure”。靠近中间的地方,颜色非常淡。白色在中间的位置,因为白色是所有彩虹色完美平衡的混合。

The white color is the limit case. Mixtures that are almost but not quite balanced will look like pastel colors, but still have a discernible shade (e.g. pastel red).

白色是极端的情况。几乎但不是完全平衡的混合将看起来像淡的颜色,但仍然后可辨别的色度(例如,淡红色)。

Now, a demonstration of how the CIE diagram format aids the “calculation” of a color mix. Figure 2 illustrates a mix of red and green.

现在,展示一下 CIE 图的格式如何帮助颜色混合的 “calculation” 。图 2 展示了红色和绿色的混合。

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Figure 2: Mix of red and green, seen as yellow

In Figure 2, we draw a line between the two exact tones involved in the mix (a shade of red and a shade of green). When these two colors reach the eyes, we cannot see them individually: we see the middleway color, a shade of yellow.

在图 2 中,我们在两个用来混合的特定的颜色之间绘制了一条线(一个红色的色度和一个绿色的色度)。当这两种颜色抵达眼睛,我们不能分别看到它们:我们看到中间的颜色,一种黄色的色度。

If we mix these colors in different proportions, the apparent color still belongs to this line, but the share will be nearer to the stronger color. For example, a mix with 75% red would render a shade of orange (a quarter way between red and green).

如果我们以不同的比例混合这些颜色,表现出来的颜色仍然属于这条线,但是分布将更接近更强的颜色。例如,一个 75% 红色的混合将渲染出一种橘黄色的色度(在红色和绿色的四分之一处)。

We can even determine the result of three-color or n-color mixes. If three colors are involved, draw a triangle and find the center of it. The mix will look like the color on this center point.

我们甚至可以确认三色或者 n 色混合的结果。如果涉及三种颜色,画一个三角形并找到它的中心点。混合色将看起来像这个中心点的颜色。

This is the strength of the CIE diagram: it allows to determine any color mix with a simple interpolation. The strange shape format and the color distribuition within the shape serve to this purpose: calculate mixes using simple straight lines.

这就是 CIE 图的力量:它允许使用简单的插值来确定任何颜色混合。它奇怪的形状和形状内的颜色分布服务于此目的:使用简单的直线计算混合。

Two details must be observed. First, the CIE diagram is valid only for human vision. For example, birds have four color receptors, and their subjective sensations to color mixes are certainly different, implying a very different CIE curve.

两个细节必须被遵守。首先,CIE 图仅对人类视觉有效。比如,鸟类有四种颜色受体,它们对颜色混合的主观感觉肯定不同,意味着非常不同的 CIE 曲线。

Second, the CIE diagram assumes additive mix, that is, combination of colored lights, not a mix of pigments. If you mix red and green paints, you won’t get yellow; you get a murky brown-violet color, because red paint is not red; it is a substance that absorbs non-red colors. Mixing paints is mixing two color filters, and the result is an even more restrictive color filter.

其次,CIE 图假设使用加法混合,即,有色光的混合,而不是颜料的混合。如果你混合红色和绿色颜料,你不会得到黄色;你得到的是一种阴暗的棕紫罗兰色,因为红色颜料不是红色;它是一种吸收非红色的物质。混合颜料是混合了两种颜色过滤器,结果是一个更严格的颜色过滤器。

Color standards for the mass market 大众市场的颜色标准

Since the human vision has three color receptors, and the CIE diagram format is roughly triangular, the most popular color reproduction methods also employ three primary colors. Two colors is too little (even though the first color movies actually used two colors, with interesting results). Four colors or more is expensive and would not yield major gains.

由于人类视觉具有三种颜色受体,并且 CIE 图的形式大概是三角形,最流行的颜色再现方法也采用了三原色。两种颜色太少(尽管第一部有色电影实际上使用了两种颜色,造成有趣的效果)。四种或更多颜色是昂贵的,也不会产生重大的收益。

Figure 3 shows the gamut of sRGB standard. It is employed in most computer monitors, digital TVs, movie and still cameras, etc. The triangle inside the diagram shows the colors that sRGB can reproduce; the arc curve represents color temperatures, a subject that we won’t discuss here.

图 3 展示了 sRGB 标准的色域。它用于大多数计算机显示器,数字电视,电影和静态照相机,等等。图中的三角形展示了 sRGB 可以重现的颜色;弧线表示色温,我们在这里不会讨论这个主题。

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Figure 3: sRGB gamut. Source: Wikipedia

First thing that we note in Figure 3 is, the triangle vertices (tips) that represent the purest colors employed in an sRGB monitor, are not in the edge of the CIE diagram, so they are not 100% pure as one would expect. This choice of impure primary colors shrinks the gamut area. In particular, the green tip is very distant from the edge, so sRGB primary green is very impure. Why’s that?

我们在图 3 中注意到的第一件事情是,表示 sRGB 显示器采用的最纯色的三角形的顶点(尖端),不在 CIE 图的边缘,所以它们不是期望中 100% 的纯色。这种不纯的原色选择缩小了色域的面积。特别地,绿色尖端离边缘非常远,所以 sRGB 的原生绿色是非常不纯的。为什么呢?

The reason is: generating pure colors is expensive . The screen “phosphors” cannot produce 100% pure reds, greens or blues. Green is the most problematic color. As we can see, the gamut of any given technology involves many decisions, including cost and mass production viability.

原因是:生成纯色是昂贵的。屏幕的“发光材料”不能生成 100% 纯的红,绿或者蓝。绿色是最有难度的颜色。如我们所见,任何给定技术的色域都涉及很多决定,包括成本和大规模生产的可行性。

In practice, the sRGB gamut is not such a crippling limitation. Even though the blue vertex in gamut does not reach violet, an sRGB screen still can show shades of violet. The only thing is, violets on the screen won’t look as saturated as e.g. violet flowers found in nature. (I have mentioned violet because it is a difficult color; lots of cameras get the colors wrong when taking pictures of violet flowers.)

在实践中, sRGB 色域没有如此严重的限制。尽管色域中的蓝色顶点没有抵达紫色,一个 sRGB 显示器仍然可以显示紫罗兰色的色度。唯一的问题是,屏幕上的紫罗兰色看起来不像自然中找到的,比如紫罗兰花,一样饱和。(我已经因为它是一种困难的颜色而提到过紫罗兰色;许多照相机拍摄紫罗兰花的照片时都得到了错误的颜色)。

The same happens with other colors not covered by the sRGB gamut. It can show shades of yellow, cyan, aquamarine, etc. The only issue is, these sRGB colors won’t be as vibrant as real-world ones. On the other hand, the gamut’s red and blue vertices are near the CIE edge, so the shades of red and blue do look pretty good on screen.

sRGB 色域中没有涵盖的其它颜色也会发生同样的情况。它可以展示黄,青,海蓝宝石等色调。唯一的问题是,这些 sRGB 颜色不像现实世界中的那样鲜艳。另一方面,色域的红色和蓝色顶点接近 CIE 边缘,所以红色和蓝色的色调在屏幕上看起来相当好。

Not that other technologies don’t try to cover more colors. Figure 4 shows the gamut of many of them.

这不是说其它技术不试图覆盖更多的颜色。图 4 展示了它们中许多的色域。

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Figure 4: Gamut of several technologies. Source: Wikipedia

Photography entusiasts are divided between sRGB and Adobe RGB, more or less like Democrats and Republicans. Good digital cameras can do Adobe RGB, but then the photographer also needs to have a screen capable of Adobe RGB gamut, otherwise edits will throw colors off-beam.

摄影支持者被分为 sRGB 和 Adobe RGB,或多或少像民主党和共和党。好的数码相机支持 Adobe RGB,但是摄影师还需要拥有一个支持 Adobe RGB 色域的显示器,否则编辑会把颜色改错。

Of course, the idea of Adobe RGB is to get a better gamut at the last step: printing. Amateur photographers need to check if the print service “understands” Adobe RGB (not always the case). Naturally, big-time book and magazine publishers have the necessary equipment to use Adobe RGB end-to-end.

当然,Adobe RGB 的想法是在最后一步获得更好的色域:打印。业余摄影师需要检查打印服务是否“理解” Adobe sRGB (并不总是这样)。自然地,大型图书和杂志出版社有使用 Adobe RBG 必要的端到端设备。

Figure 5 shows a cyan-green sRGB gradient. Clicking or touching the image toggles between Adobe RGB and sRGB versions. Both images are exactly the same, only the color profile is different.

图 5 展示了一个青绿色的梯度。点击或者触摸图片会在 Adobe RGB 和 sRGB 版本间切换。两个图片完全相同,只有 color profile 不同。

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Figure 5: sRGB and Adobe RGB gradients. Click or touch the image to toggle between them.

You will only see a difference if the screen and the browser and the operating system support Adobe RGB. For example, I could see a difference in Safari for Mac, but not in Chrome for Mac. You can try to download both images and compare them using other software. Still talking about Macs, Preview and iPhoto show differences, but not Gimp. I was actually surprised to see any differences in my monitor since it is not a “pro” model.

只有在显示器和浏览器和操作系统支持 Adobe RGB 时你会看到差别。例如,我可以在 Safari for Mac 上看到差别,但是在 Chrome for Mac 上看到不。你可以试着下载这两张图片,使用其它软件比较它们。继续讨论 Macs ,Preview 和 iPhoto 展示出了差异,但是 Gimp 没有。我真的很惊讶在我的显示器上看到任何差异,因为它不是一个 “pro” 模型。

On the other hand, the sRGB image on Chrome shows the same vibrant green of the Adobe RGB image in Safari. While Safari obeys the strict limits of sRGB, Chrome (and most other software, as well as all mobile devices) shows the most vibrant colors available. An explicit conversion from Adobe RGB to sRGB could generate bland images on the end user’s screen.

另一方面, Chrome 上的 sRGB 图像展示了和 Adobe RGB 同样鲜艳的绿色。Safari 遵循了 sRGB 的严格限制,而 Chrome(以及大多其它晚间,以及所有的移动设备)展示了可用的最鲜艳的颜色。从 Adobe RGB 到 sRGB 的显式转换会在用户终端显示器上生成乏味的图像。

In order to stress the point, there goes another example: a yellow furniture. Saturated yellow is another color that Adobe RGB can show, and sRGB cannot. I took two pictures of the same object, one with Adobe RGB configured in-camera, another one sRGB. The following images are the original camera files:

为了强调这一点,还有另外一个例子:一个黄色的家具。饱和的黄色是 Adobe RGB 可以展示而 sRGB 不能展示的另外一个颜色。我拍了同一个物体的两张图片,一个使用相机中配置的 Adobe RGB,另一次使用 sRGB。以下的图像是原始的相机文件:

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Figure 6: Yellow furniture, Adobe RGB

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Figure 7: Yellow furniture, sRGB

In Safari or Preview, Figure 7 shows a dull yellow that does not make justice to the actual object. This is expected due to sRGB limitations. But in Chrome and iPhone 5, Figure 6 shows a greenish yellow, while Figure 7 looks ok.

在 Safari 或者 Preview 中,图 7 显示了一种和实际对象不符的暗淡的黄色。由于 sRGB 的限制这是符合预期的。但是在 Chrome 和 iPhone 5 中,图 6 显示了一种仓黄色,而图 7 是好的。

Then, I took a number of screenshots, to try to illustrate how these pictures can look different according to color profile and viewing software. Since a screenshot captures the “native” pixel values post-monitor calibration, Figures 8 and 9 may present weird colors in your screen.

然后,我取了一些截图,试图说明依赖不同的 color profile 和查看软件,这些图片看起来是多么不同。由于屏幕截图软件捕获了后监视器校准后的“原始”像素值,图 8 和 9 可能会在屏幕上显示奇怪的颜色。

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Figure 8: Screenshot of Adobe RGB image in Preview

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Figure 9: Screenshot of sRGB image in Preview

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Figure 10: Screenshot of Adobe RGB image in Chrome

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Figure 11: Screenshot of sRGB image in Chrome

On my monitor, Figure 8 looks best. This is expected since everything conjures up for this result. But Figure 11 looks pretty good, too. In iPhone 5, Figure 11 is definitively the best. In a Galaxy Nexus, Figure 9 looks most faithful.

在我的显示器上,图 8 看起来最好。这是符合预期的,因为一切都在促成这个结果。但是图 11 看起来也相当好。在 iPhone 5 上,图11 是最好的。在 Galaxy Nexus 上,图 9 看起来最正确。

These technology blunders justify the pragmatic advice of using only sRGB when the destination of your pictures is the Web or a screen.

这些技术偏差,证明了当你的图片的目的是 Web 或者显示器时,只使用 sRGB 的务实的建议。

Even more colors! 甚至更多颜色!

It is also worth of mention the Wide Gamut RGB system , also created by Adobe. This system specifies pure primary colors, creating an enormous gamut. As we said before, pure colors are difficult to generate, but the techological evolution will solve this problem in time. For example, OLED screens already have wider gamut than LCDs. (By now, the biggest issue with OLEDs is being too expensive for big screens.)

还值得一提的是 Wide Gamut RGB 系统,同样由 Adobe 创建。该系统规范了纯原色,创造了一个巨大的色域。如我们此前所说,纯色难以生成,但是技术演变会及时解决这个问题。例如,OLED 屏幕已经有比 LCDs 更宽的色域。(目前为止,OLEDs 最大的问题是对于大屏幕来说太贵了)。

Due to the CIE diagram format, that just reflects how the human vision works, even using four, five or more primary colors is not enough to cover 100% of color spectra, since the gamut is always a polygon, and a polygon can’t fill a curved shape. Of course, using more colors does increase the gamut and new technologies try this way from time to time.

由于只反映了人类视觉工作原理的的 CIE 图的形式,即使使用四个,五个或者更多原色也不足以覆盖 100% 的色谱,因为色域总是一个多边形,而一个多边形不能够填充一个弯曲的形状。当然,使用更多颜色确实增加了色域,新技术也在不断尝试这种方式。

Impossible colors 不可能的颜色

The ProPhoto gamut, also present in Figure 4, adopts a funny strategy to increase gamut: only three primary colors, but two of them are “imaginary colors”, that a normal human being cannot see. It employs a super-blue and a super-green.

ProPhoto 色域,也出现在图 4 中,采用一种有趣的策略来增加色域:只有三种原色,但其中两种是正常人不能看到的 “假想色”。它采用了一种超级蓝和一种超级绿。

What are those “imaginary colors”? They are colors with saturation higher than we can normally perceive.

这些 “假想色” 是什么?它们是饱和度高于我们通常可以感知到的原色。

The color receptors in our eyes are not perfect either, and they are a bit stimulated by the opposite colors as well. For example, the green receptors are slightly sensitive to violet, they register some light even if we look to a violet monochromatic laser. So, we perceive that pure violet with 99.9% of purity, but never 100%.

我们眼睛中的颜色受体也不是完美的,它们也会被相反的颜色刺激到一点。比如,绿色受体对紫罗兰色略微敏感,即使我们看到紫色单色激光它们也会暂存一些光。所以,我们感知到的纯紫罗兰色有 99.9% 的纯度,但从未到 100%。

But an artificial sensor, like a camera, can see colors better than a human, so it can define its own gamut based on the most pure primary colors that it can distinguish.

但是一个人工传感器,如相机,可以比人类更好地看到颜色,所以它能够基于它可以分辨的最纯的原色,定义它自己的色域。

The only problem is, the reproduction of these “imaginary colors” wouldn’t be seen by anybody. A printed super-blue looks just like ordinary blue. But that’s ok. The idea of using super-primary-colors is to cover more of those saturated secondary colors that are visible, like saturated cyans and yellows.

唯一的问题是,这些“假想色”的再现不会被任何人看到。一个打印的超蓝色看起来就像普通蓝色。但是没关系。使用超原色的想法就是覆盖更多那些可见的饱和二级色,如饱和的青紫和黄色。

There is a trick to see a “super color”. For example, to see a super-green, cover your entire screen with magenta (using any means, like Paint or Photoshop) and make another full-screen image that is green. Keep looking at the magenta image for two minutes, then switch fast to the green image. Since the red and blue receptors were “worn off” by the magenta, they will black out and you will see a green that is more saturated (pure) than usual.

有一个看到“超级颜色”的窍门。例如,为了看到超绿色,用洋红色覆盖你的整个屏幕(使用任何方法,如 Paint 或 Photoshop),同时准备另一张全屏的绿色图像。持续观察洋红色的图像两分钟,然后快速切换到绿色图像。由于红色和蓝色受体被洋红色致“疲劳”,它们会昏厥然后你讲看到比平常更饱和(纯)的绿色。

The same trick can be employed to see saturated shades of yellow and cyan that normally cannot be reproduced by an sRGB monitor.

可以使用同样的技巧来观察通常不能由 sRGB 显示器再现的黄色和青色的饱和色度。

The big problem: color printing 大问题:彩色打印

The CMYK printing technology, present in books, magazines, printers, etc. has the best cost-benefit relationship. But CMYK is very limited in gamut. It surpasses sRGB only in saturated cyan and yellow, since these are primary CMYK colors. Reds, greens and blues look somewhat dull in CMYK.

CMYK 印刷技术,存在于书、杂志、打印机等等,有最好的成本收益关系。但是 CMYK 在色域上非常有限。它尽在饱和的青色和黄色上超过了 sRGB,因为这是主要的 CMYK 颜色。红色、绿色和蓝色在 CMYK 上看起来有些暗淡。

Subtrative color mix is, by itself, a problem for gamut. Likewise the primary sRGB colors, CMYK pigments are not perfect. The purest and more exact a pigment, the more expensive it is. Just look at the price of a typical inkjet printer cartridge.

减色混合本身就有色域上的问题。和主要的 sRGB 颜色类似,CMYK 颜料不是完美的。一种颜料越纯越精确,就越昂贵,只要去看一个典型的喷墨打印机墨盒的价格。

To achieve a wider print gamut, the solution is to use more primary pigments. The Hexachrome system adds green and orange to CMYK. The Pantone color pallete, widely used as authoritative color reference for everything, including national flags, employs no less than 14 different pigments.

为了获得更广泛的打印色域,解决方案是使用更多原颜料。Hexachrome 系统在 CMYK 中添加了绿色和橘黄色。Pantone 调色板——广泛用户所有东西的权威颜色参考,包括过期,至少采用了 14 种不同的颜料。

Photographic film (now obsolete) and paper have the reputation of delivering wider gamut than current digital technologies. In particular, the slide film has great saturated colors.

摄影胶片(现已废弃)和纸张有比当前的数字技术提供更广泛色域的名声。特别地,滑动胶片有很好的饱和色。

It is interesting to note that films also employ subtractive mix of three colors. Probably, two details of the processing compensate this limitation. First, a film is “read” by transparency, while in a print the light must cross the pigments twice and be reflected by the paper. Second detail is that every batch of film or photographic paper is tested and compensated for color correction, so any small deviation in pigments is compensated for.

有趣的是,胶片也采用了三种颜色的减法混合。可能,处理中的两个细节补偿了这个限制。首先,胶片是被透明“阅读”的,而在打印中光线必须两次穿过颜料被纸张反射。第二个细节是每一批胶片或者相纸都要经过颜色矫正的测试和补偿,补偿了颜料中小的偏差。

A residual problem in photographic film is the loss of gamut space when they are scanned, since the scanner will have its own gamut limitations (it can be sRGB-only). This will rob some of the original colors.

摄影胶片残留的一个问题是当它们被扫描时色域空间的损失,因为扫描仪有它自己的色域限制(它可能仅支持 sRGB)。这会夺走一些原始的色彩。

Violet 紫罗兰色

I have mentioned that violet is a “difficult” color. Many digital cameras, at least the older ones, struggle with reproduction of certain tones of “purple”. You probably had taken a picture of a purple flower and it looks blue on-screen.

我已经提到过紫罗兰色是一种“困难”的颜色。许多数码相机,至少老的数码相机,努力重现某些“紫色”的色调。你可能拍了一幅紫色花朵的照片,它在屏幕上看起来像蓝色的。

First thing is, we tend to name “purple” a range of colors that are spectrally very different, like violet, purple, pink, magenta, rose, lavender, etc. Violet is a true color, it lies between blue and ultraviolet. The other colors are mixtures of violet and red, or blue and red, that our brain recognizes as sui generis colors.

首先,我们倾向于把一些列光谱非常不同的颜色命名为“紫色”,像紫罗兰色、紫色、粉红色、洋红色、玫红色、薰衣草色等。紫罗兰色是一个真正的颜色,它位于蓝色和紫外线之间。其它颜色是紫罗兰色和红色,或者蓝色和红色的混合,我们的大脑把它们识别成独特的颜色。

To make things more complicated, our eyes can be “fooled” by a mix of dark blue and a little bit of red. This mix looks violet, though less saturated than the spectral violet. So, when we see a violet-like object, it is impossible to tell whether it is really violet or blue+red. (We can know for sure by using a red light; if the object is truly violet, it will look almost black under red light.)

让事情更复杂的是,我们的眼睛会被暗蓝色和一点红色的混合“愚弄”。这个混合物看起来像紫罗兰色,尽管比光谱中的紫罗兰色欠饱和一点。所以,当我们看到一个像紫罗兰色的物体,不可能分辨出它是真是的紫罗兰色还是蓝色+红色。(我们可以通过使用一个红色的等确定;如果这个物体是真正的紫罗兰色,它在红灯下将看起来几乎是黑色的。)

Every color technology reproduces magenta or pink without issues; it is just a matter of mixing red and blue in correct proportion. The same happens for non-saturated violets like lavender. The most saturated the desired violet, the more difficult is to reproduce it, at least with standard equipment.

每种颜色技术重现品红色或者粉红色都没有问题,它仅是红色和蓝色以正确比例的混合。对于非饱和的紫罗兰色也是如此。期望的紫罗兰色越饱和,就越难重现它,至少使用标准的设备是如此。

A way to extend RGB technology into violets (and increase its gamut) is to use violet as the “B” primary color. That’s what the Wide Gamut RGB does. In this system, blue is generated by a mix of violet and green. Three practical issues: violet dyes and light sources are more expensive; the human eye is poorly sensitive to violet, so more power is necessary to achieve the same apparent brightness; and intense violet light can damage the eye (not only UV, but also strong violet and blue light are bad for your eyes).

一种将 RGB 技术扩展到紫罗兰色的方法(并增加其色域)是使用紫罗兰色作为“B”原色。 Wide Gamut RGB 就是这么做的。在这个系统里,蓝色由紫罗兰色和绿色的混合生成,三个实践问题:紫罗兰色和光源更昂贵;人类眼睛对于紫罗兰色不敏感,因此需要更多的力度来获得相同的表观亮度;而且强烈的紫罗兰光会损伤眼睛(不仅 UV,强烈和紫罗兰和蓝光对你的眼睛也是有害的)。

Reproducing violet is difficult; capturing it is an even bigger challenge, because the typical Bayer sensor has red, green and blue pixels. Violet light excites only the blue pixels, and the camera “sees” violet as a very pure blue. That’s why older digital cameras confuse the two colors.

重现紫罗兰色是困难的;捕获它甚至是更大的挑战,因为典型的 Bayer 传感器有红色、绿色和蓝色像素。紫外线光只会是蓝色像素感光,相机把紫罗兰“看成“一种非常纯的蓝色。这就是为什么老的数码相机会混淆这两种颜色。

The human eye can tell violet apart from blue since the “blue” (S) receptors are actually more sensitive to violet, and the “green” (M) receptors are quite sensitive to blue, but not to violet. The brain can distinguish violet from blue by the difference of response between S and M.

人眼可以区分紫罗兰色和蓝色,因为“蓝色”(S)受体实际对紫罗兰色更敏感,而“绿色”(M)受体对蓝色很敏感,对紫罗兰色则不敏感。大脑可以根据 S 和 M 响应的差异来区分紫罗兰色和蓝色。

Moreover, in relative terms, the “red” (L) receptors are more sensitive to violet than the “green” (M) ones. (The absolute sensitivity of all 3 receptors to spectral violet is very low, so it is always perceived as a dark color.) This is the probable reason why a mix of red and blue passes off as violet or purple-like.

此外,相对而言,“红色”(L)受体对紫罗兰色比“绿色”(M)更敏感。(3种受体对光谱中紫罗兰色的敏感度都非常低,因此它总被感知为深色。)这是为什么红色和蓝色的混合会被仿冒成紫罗兰色或者类似紫色的可能的原因。

Since we have mentioned it, it is interesting to clarify that L receptors are not very sensitive to red; they are most sensitive to lemon-green! As happens with violet, the red color is perceived as a dark color because the L receptor is (poorly) sensitive to it; the M and S receptors are completely blind to red. The M receptor is most sentitive to bluish green, and S receptor is most sensitive to blue-violet.

既然我们已经提到这里,有趣的是澄清 L 受体对红色不是非常敏感;它们对柠檬绿最敏感!与紫罗兰色一样,红色被感知为一种暗色因为 L 受体对它(不足够)敏感,M 和 S 受体对红色完全是盲目的。M 受体对蓝绿色最敏感,S 受体对蓝紫罗兰色最敏感。

Current digital cameras can also distinguish violet in some fashion, even though the details are scarce (each manufacturer has its own “secret sauce”). Three major strategies are possible: 1) use violet pixels instead of blue ones; 2) consider that green pixels are a bit sensitive to blue but not to violet; 3) use red pixels with dyes that let violet pass through as well.

当前的数码相机可以以某种方式分区紫罗兰色,尽管细节很稀少(每个制造商都有自己的“秘密武器”)。三个主要的策略是有可能的:1)使用紫罗兰像素替代蓝色;2)考虑绿色像素对蓝色更敏感而不是紫罗兰色;3)使用的红色像素有让紫罗兰色也可以通过的颜料。