What is the magical principle that the printer can print millions of colors with only four inks?
The core lies in the print head. There are a large number of head distributed on the shower head, and each head is thinner than a hair. The head are designed to be wide at the top and narrow at the bottom, which creates a negative pressure that prevents ink from leaking. Once printing starts, the upper heating resistor will heat the temperature to 100 degrees within 0.00001 second. The high temperature evaporates the nearby ink and forms air bubbles. The air bubbles act as pistons to push the lower ink out of the ink droplets. Due to the viscosity a main drop and a trailing drop are formed. They fall at a speed of ten meters per second, and the head is one millimeter away from the paper, so it only takes one ten-thousandth of a second to reach and be absorbed by the paper in a very short time. The head is connected to the printer through a hose, the belt and pulley are driven by a stepping motor to move the head, and a shaft stepper is added to move the paper. This is the basic structure of the printer.
How to print colorful images with four inks?
You might think of using a red-green-blue mix. Let's do a small experiment first. If you add red and green flashlights together, you will get yellow when mixed, but if you mix red and green inks, you will get a very cloudy yellow. In fact, this is the difference between additive color mixing and subtractive color mixing. For self-illuminating shades, mixing two colors will increase the brightness, and the ink itself will not emit light. We can see the color of the ink because the light hits the ink first, and when it is reflected to the human eye, this process will filter out part of it. For a better understanding, we zoom in on the ink droplet to a microscopic perspective. If the green molecules in the lower layer want to reflect green light, they must penetrate the green and red molecules in the upper layer, but this process will be blocked by the red molecules, and black will be produced in this area. Likewise, the red molecules in the lower layer are blocked by the green molecules in the upper layer, and the resulting black is what causes the yellow to become cloudy.
To give another popular example, the gray hair we see with the naked eye is actually the result of mixing white and black hair, so obviously, the three primary colors of red, green and blue cannot be directly used on the printer. The solution is simple, just replace red, green and blue with complementary colors, cyan, magenta and yellow. When the nozzle releases a droplet of cyan ink, followed by a droplet of yellow ink quickly, the two mix together to create the heady green color. The diameter of the mixed ink droplet is only 0.05 mm, and various colors can be obtained in this way.
What if I want a lighter green?
In fact, as long as the spacing is increased, a lighter green can be obtained, and vice versa, it will become darker, but the spacing is always limited.
What if you want a darker green?
At this time, black ink comes in handy. Mixing black into green ink droplets will result in dark green. The more black you mix, the darker the green will be. So as long as you use 4 colors of CMYK, you can print hundreds of colors at most. Tens of thousands of colors, and an A4-sized photo can even have hundreds of millions of ink droplets. I have to admire the wisdom of human beings.
