You might have heard that light is a kind of wave and that the color of an object is related to the frequency of light waves it reflects. High-frequency light waves look violet, low-frequency light waves look red, and in-between frequencies look yellow, green, orange, and so on. You might call this idea physical color because it says that color is a physical property of light itself. It's not dependent on human perception. And, while this isn't wrong, it isn't quite the whole story either. For instance, you might have seen this picture before. As you can see, the region where the red and green lights overlap is yellow. When you think about it, this is pretty weird. Because light is a wave, two different frequencies shouldn't interact with each other at all, they should just co-exist like singers singing in harmony. So, in this yellow looking region, two different kinds of light waves are present: one with a red frequency, and one with a green frequency. There is no yellow light present at all. So, how come this region, where the red and green lights mix, looks yellow to us? To understand this, you have to understand a little bit about biology, in particular, about how humans see color. Light perception happens in a paper-thin layer of cells, called the retina, that covers the back of your eyeball. In the retina, there are two different types of light-detecting cells: rods and cones. The rods are used for seeing in low-light conditions, and there is only one kind of those. The cones, however, are a different story. There three kinds of cone cells that roughly correspond to the colors red, green, and blue. When you see a color, each cone sends its own distinct signal to your brain. For example, suppose that yellow light, that is real yellow light, with a yellow frequency, is shining on your eye. You don't have a cone specifically for detecting yellow, but yellow is kind of close to green and also kind of close to red, so both the red and green cones get activated, and each sends a signal to your brain saying so. Of course, there is another way to activate the red cones and the green cones simultaneously: if both red light and green light are present at the same time. The point is, your brain receives the same signal, regardless of whether you see light that has the yellow frequency or light that is a mixture of the green and red frequencies. That's why, for light, red plus green equals yellow. And, how come you can't detect colors when it's dark? Well, the rod cells in your retina take over in low-light conditions. You only have one kind of rod cell, and so there is one type of signal that can get sent to your brain: light or no light. Having only one kind of light detector doesn't leave any room for seeing color. There are infinitely many different physical colors, but, because we only have three kinds of cones, the brain can be tricked into thinking it's seeing any color by carefully adding together the right combination of just three colors: red, green, and blue. This property of human vision is really useful in the real world. For example, TV manufacturing. Instead of having to put infinitely many colors in your TV set to simulate the real world, TV manufacturers only have to put three: red, green, and blue, which is lucky for them, really.
你可能听过光具有波动性, 而物体的颜色取决于 该物体反射出光线的频率 高频率的光波看起来是紫色, 低频率的光波看起来是红色, 而且两者中间的频率看起来可能是黄色、 绿色、 橘色 等颜色 你可以说这是物理性的颜色, 因为它表示光的颜色源自于本身属性 和人类解读能力没有关系 虽然这并非错误, 但是不能完全解释人如何辨别颜色 举例而言,你可能看过这张图 如你所见,红色和绿色光叠加看起来是黄色 但如果你仔细思考,就会觉得怪怪的 因为光具波动性,两种不同频率的光波 不应该会有交互作用, 它们应该像是合唱演出般 共同存在 所以,在你看起来是黄色的区域 有两种光波存在: 一种是红光光波 另一种是绿光光波 但这里并无黄光光波的存在 那为什么这个 红色和绿色迭加的区域 看起来会是黄色呢? 要了解这个现象,必须先了解生物学 尤其是关于人如何看到颜色的部份 光由人类眼球底部 薄薄一层 被称为视网膜的细胞所接收 在视网膜上有两种感光细胞 杆状细胞和锥状细胞, 其中杆状细胞在低亮度时 负责接收, 而且只有一种 而锥状细胞就有所不同了! 我们有三种锥状细胞, 他们分别对应红色、 绿色、 和蓝色 当你看到颜色时, 不同的锥状细胞会将不同的讯息送向脑部 举例而言, 当有一道真正具有黄色频率的光线 射入你眼睛时, 你并没有专门负责接收黄光的锥状细胞 但是因为黄色和绿色 及红色相近, 所以负责红色和绿色的锥状细胞会被活化, 分别传送讯息到你的脑部 当然,有另一种方式可以达到相同效果: 红色和绿色光同时抵达, 造成负责红色和绿色的锥状细胞同时被启动 这时候脑部会收到相同的讯号, 不论是接受一束黄光 或是由红光和绿光所混成的光线都是一样 所以对光线来说,红色加绿色就成了黄色 那为何你无法在黑暗中辨别色彩呢? 这是因为在低亮度的状况下 是由视网膜上的杆状细胞接手感光 但是你只有一种杆状细胞, 所以它只能送出一种讯号 告诉你的大脑 是亮还是暗 因为只有一种侦测器, 所以没办法侦测看到的颜色 物理颜色近乎无限多种, 而我们只有三种锥状细胞, 大脑则藉由运算 红、绿、蓝 这讯号强弱相加的结果 让我们看到不同色彩 人类视觉原理在真实世界中十分有用 例如:电视机的制造 与其要放进无限种颜色的光源 以仿真真实世界的色彩 电视制造商只需要用到三种光源: 红、绿、蓝 这对他们来说真是太幸运了!