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.
你可能聽過光具有波動性, 而物體的顏色取決於 該物體反射出光線的頻率。 高頻率的光波看起來是紫色, 低頻率的光波看起來是紅色, 而且兩者中間的頻率看起來可能是黃色、 綠色、 橘色 等顏色。 你可以說這是物理性的顏色, 因為它表示光的顏色源自於本身屬性。 和人類解讀能力沒有關係。 雖然這並非錯誤, 但是不能完全解釋人如何辨別顏色。 舉例而言,你可能看過這張圖。 如你所見,紅色和綠色光疊加看起來是黃色。 但如果你仔細思考,就會覺得怪怪的。 因為光具波動性,兩種不同頻率的光波 不應該會有交互作用, 它們應該像是合唱演出般 共同存在。 所以,在你看起來是黃色的區域 有兩種光波存在: 一種是紅光光波 另一種是綠光光波。 但這裡並無黃光光波的存在 那為什麼這個 紅色和綠色疊加的區域 看起來會是黃色呢? 要瞭解這個現象,必須先學學生物學—— 尤其是關於人如何看到顏色的部份。 光由人類眼球底部 薄薄一層 被稱為視網膜的細胞所接收。 在視網膜上有兩種感光細胞 桿狀細胞和錐狀細胞, 其中桿狀細胞在低亮度時 負責接收, 而且只有一種。 而錐狀細胞就有所不同了! 我們有三種錐狀細胞, 他們分別對應紅色、 綠色、 和藍色。 當你看到顏色時, 不同的錐狀細胞會將不同的訊息送向腦部。 舉例而言, 當有一道真正具有黃色頻率的光線 射入你眼睛時, 你並沒有專門負責接收黃光的錐狀細胞。 但是因為黃色和綠色 及紅色相近, 所以負責紅色和綠色的錐狀細胞會被活化, 分別傳送訊息到你的腦部。 當然,有另一種方式可以達到相同效果: 紅色和綠色光同時抵達, 造成負責紅色和綠色的錐狀細胞同時被啓動。 這時候腦部會收到相同的訊號, 不論是接受一束黃光 或是由紅光和綠光所混成的光線都是一樣。 所以對光線來說,紅色加綠色就成了黃色。 那為何你無法在黑暗中辨別色彩呢? 這是因為在低亮度的狀況下 是由視網膜上的桿狀細胞接手感光。 但是你只有一種桿狀細胞, 所以它只能送出一種訊號 告訴你的大腦 是亮還是暗。 因為只有一種偵測器, 所以沒辦法偵測看到的顏色。 物理顏色近乎無限多種, 而我們只有三種錐狀細胞, 大腦則藉由運算 紅、綠、藍 這訊號強弱相加的結果 讓我們看到不同色彩。 人類視覺原理在真實世界中十分有用。 例如:電視機的製造。 與其要放進無限種顏色的光源 以模擬真實世界的色彩。 電視製造商只需要用到三種光源: 紅、綠、藍。 這對他們來說真是太幸運了!