Rebirth of top photographers

Chapter 185: The Color Principle of Photography (Essential! Colorful)
"Color is actually an optical concept in physics."

Chen Pingsheng's first sentence brought everyone into thinking.Everyone tried their best to recall the knowledge taught by their high school physics professor, but found that their brains were blank.

It can only be said that the peak period of knowledge for many people is in high school, but once they go to college, they have nothing.

"What does it mean?" Chen Pingsheng explained to everyone: "The color we see is actually the light reflected into our eyes and stimulates the cones in the eyeballs. When visible light enters the retina of our eyes, The cones are activated and relay information to the brain.

"Of course, the naked eye cannot sense all light, such as infrared and ultraviolet rays, we just can't see it."

Chen Pingsheng clicked on the next page, which showed a spectrum table.

"The human eye can accept electromagnetic waves in the range of 380nm-780nm, because light is actually electromagnetic waves. This part is also called the visible spectrum."

"Then what's the use of this?" Chen Pingsheng said with a smile: "Because the opsins in our cone cells can detect electromagnetic waves of different wavelengths and then sense three colors, namely red, green and blue.

"And the bandwidth that we can feel for the three light frequencies of red, green and blue is actually the largest. You can look at this table."

Chen Pingsheng pointed to the ppt, which showed a spectrum of red, green and blue, indicating the range that the human eye can distinguish.

"As you can see, red, green, and blue have the largest ranges, while yellow has only a very narrow range. That's why we think that red, green, and blue are the three primary colors. Expressed in English, that is, red, green, Blue, did you think of something?"

Chen Pingsheng raised his finger: "Yes, it's RGB."

Some students were stunned, and some nodded. Although these knowledge were taught in their freshman year, they just didn't explain it as clearly as Chen Pingsheng, so now they can completely follow his ideas.

Then I heard Chen Pingshi raise the question again: "So what are the red, yellow and blue we have been learning from primary school? Why do we all learn in art that the three primary colors are red, yellow and blue?"

"If you want to understand this, you still have to start with RGB. Red, green, and blue can be understood as an additive color mode. What is an additive color mode? Let me give you an example.

"Suppose there are three flashlights in front of us. They can emit red light, green light, and blue light respectively. When we shine the three flashlights together, a white light will be mixed. Why white light? Everyone knows Newton Sunlight is separated into many colors using a prism, among which the most obvious ones we see are red, green and blue.

"So when we mix three colors at this time, is it equivalent to restoring sunlight? In fact, the principle here is that red, green and blue cover the entire visible spectrum, so it becomes white. And this is called the additive color mode. "

Chen Pingsheng continued to click on the next page of the ppt: "When will I use the additive color mode now, that is, TV, computer, and mobile phone screens. Because they emit light by themselves, manufacturers use RGB as the three primary colors. When they are lit together, they become white. .”

"Of course we can also do an experiment. It's very simple. Take out your mobile phone and drop a very small drop of water on the screen. Not very big, but very small. Then the screen of the mobile phone should be white. If you look carefully at this time, you will see Three colors, red, green and blue, were found in it. In fact, this drop of water acted as the prism in Newton's hand."

At this point, he paused for a while, because the students below had already taken out their mobile phones to do experiments.

Chen Dong happened to bring a bottle of water. When he heard this, he immediately clicked a drop on the screen and then lit up the screen.

"You are not white!" Li Yuanmei reminded him.

"Oh, that's right." Chen Dong immediately found a white wallpaper and added another drop.

Then he raised his phone, and sure enough he found red, green and blue colors in the water droplets.

"It really does!" Other students also completed the experiments at this time, some were successful and some failed, but everyone had no doubts about the experimental results and were convinced by Chen Pingsheng's words.

I didn’t expect that this little thing with three primary colors would be born like this.

Seeing this, Chen Pingsheng continued: "Everyone should have seen it, so red, green and blue RGB are also called the three primary colors of light and color. So what do the three primary colors in art mean? The next step may be a bit brain-burning, you can use your mobile phone to Make a note of it.”

After hearing this, everyone immediately picked up their mobile phones and started video and recording.

Chen Pingsheng smiled slightly: "We just said that when the three colors of red, green and blue are added together, white will be formed in the end. So on the other hand, what will happen if the printing pigments are added like this?"

"It will turn black!" one student replied. "That's right, no matter how you add red and blue, green and blue, you will only get a color darker than the original color. We don't care what color it is, everyone just needs to know that the paint phase It will become darker and darker until it becomes black.

"So if we want to print, we have to find colors lighter than red, green and blue, and those colors must also be able to produce red, green and blue. If we think about it this way, we understand that we cannot use red, green and blue. As a color, what color should we use?
"So someone discovered these three colors."

Chen Pingsheng pressed the remote control, and the ppt immediately displayed three new colors.

"Cyan, magenta, yellow. That's cyan and magenta."

At this point, Chen Pingsheng raised his voice and said: "Be careful, what follows will sound a bit convoluted, I will try to explain it as clearly as possible."

"Why are these three colors used? Because when printing, a yellow pigment is painted on white paper. This pigment itself does not emit light. It actually absorbs, or reduces, the white light that shines on it. Blue light reflects green and red light. There are three primary colors of red, yellow and blue in white light. No matter why it absorbs blue light, we only need to know, what does green light plus red light equal? ​​Yellow light, that is, it is in us The cause of the yellow color in vision.

"In the same way, the cyan pigment reflects the green light plus blue light in the white light, and the magenta pigment reflects the red light plus the blue light, so it appears this color."

When Chen Pingsheng finished speaking, the ppt listed several equations in a timely manner.

But the expressions of the students began to change a little, because they were thinking hard about this paragraph, and this explanation was really convoluted.

Chen Pingsheng said: "You don't need to understand the reasons for the time being, you just need to write them down, because after all, we are not engaged in research and development. These things are just to give everyone an idea."

"Anyway, this is a math problem. The most important thing is that we now know that cyan, magenta, and yellow are the three primary colors of printing. So how do we call them? Generally, we will say the three primary colors of pigments and the three primary colors of color. In English, the abbreviation is CMY, and the three of them are subtractive color modes.”

"You must be familiar with CMY, right? You can often see it in PS. When printing homework, the teacher will also emphasize the use of CMYK mode. Everyone knows that CMY is printing the three primary colors, but what about K?"

Chen Pingsheng flipped the page, and the four colors of CMYK were on the screen.

"Actually, K refers to black. Because in printing, black is the most difficult color to mix. First of all, for this color, three colors of cyan, magenta, and yellow need to be mixed, which is very wasteful. And even if we mix the three primary colors together, Because of the paper, it is difficult to mix pure black and can only get a dark brown. So the manufacturer simply lists black separately.

"As for why it's called K, not B. One theory is because it needs to be distinguished from blue, and another theory is that black is the keyboard. So instead of using B, K is used."

"So far, we have figured out CMYK and RGB. The additive color mode RGB, red, green and blue, they are self-illuminating. The subtractive color mode CMY, cyan magenta yellow, they are reflected light."

All the students nodded, and even some of the young teachers nodded slightly, indicating that two simple sentences and two nouns in the book had so many meanings.

Chen Pingsheng continued to turn the pages. Above was a PS color balance panel.

"Then, now comes our most important step. Looking at this panel, we can see that cyan, magenta, yellow, red, green, and blue exactly correspond to each other."

In the picture, there is a color line between cyan and red, with a triangular pointer in the middle, which looks like a seesaw.

"Cyan corresponds to red, magenta is also called magenta corresponds to green, and yellow corresponds to blue." Chen Pingsheng pointed them out for everyone one by one, and then said: "This is actually completely consistent with the corresponding relationship in the color wheel."

"Our human eyes are accustomed to white light. When we look at a single color for a long time, the brain will automatically supplement the missing color. This color is the complementary color of red, so what is the complementary color of red? It is on the color wheel , the color 180 degrees opposite it is cyan.”

"But some people say it's wrong, saying that the complementary color of red is obviously green. Which is the complementary color of red, cyan or green?"

Chen Pingsheng looked at the color circle and said: "Actually, they are all right, because the complementary color of green is magenta. This color is actually not much different from red in terms of senses. Many people also think of it as red. So many people who don't know what it is. People, would say the complementary color of red is green.”

"And many older textbooks also use green as the complementary color of red, especially painting textbooks. Because when an artist paints, he acts based on his feelings. He does not consider the RGB value of the color, only the RGB value of the color. Few painters are so rigorous."

"So it is passed down that the complementary color of red becomes green. And we also know that throughout the ages, there are many masters of painting at home and abroad who have used red and green as complementary colors to paint many famous paintings. This is one of the reasons why this statement is widely circulated. "

Chen Pingsheng turned around and looked at the junior students present: "Now that we understand complementary colors, I will tell you a very useful color adjustment method in post-photography."

(End of this chapter)