Why not print in RGB?

RGB is additive color and CMYK is subtractive color. Simply put, RGB means that the three colors add up to white, and CMYK is black ~

Their principles are different. Since the landlord says he knows something, he must know that the display generally uses RGB, because the display is a light source that directly shoots colored light into our eyes. CMYK is used for printing, because printing is that the object absorbs some colored light, and the rest is reflected to our eyes, which is the color we see.

Plain paper is white at first, which means that any color of light is reflected. When we look at the screen of a computer monitor or TV set with a magnifying glass, we will see a large number of dots divided into three colors: red, green and blue. All the colors on the screen, that is, all the image contents we see, are fused by them.

All the colors on the computer screen are composed of red, green and blue light in different proportions. A group of red, green and blue is the smallest display unit.

Any color on the screen can be recorded and expressed by a set of RGB values.

Red, green and blue are also called the three primary colors of light, which are R (red), G (green) and B (blue) respectively in English.

Think of RGB as sugar, salt and monosodium glutamate in Chinese food, and any dish is a mixture of these three seasonings.

When cooking different dishes, the proportion of the three is different, and may even be very different.

So in different images, the composition of RGB is different. Some images may have more R (red) components, while others have more B (blue) components.

When cooking, the menu will prompt something like "3 grams of sugar, 65438+ 0 grams of salt" to indicate the amount of seasoning.

In the computer, the so-called "how much" of RGB refers to brightness, which is expressed as an integer.

Under normal circumstances, RGB has 256 levels of brightness, represented by the number 0, 1, 2 ... to 255.

Note that although the highest number is 255, 0 is also one of the values, so it is ***256. Just as from 2000 to 20 10 * * is 1 1 year.

According to calculation, 256 RGB colors can be combined into about16.78 million colors, that is, 256× 256× 256 =16777216.

That is commonly known as160,000 colors or10,000,000 colors. Also known as 24-bit color (2 to the 24th power).

24-bit color also has a strange name: 8-bit channel color. Why?

The so-called channel here actually refers to the respective brightness ranges of three colors of light. We know that its range is 256, and 256 is the eighth power of 2, which is called 8-bit channel color.

Why is it always expressed as a power of 2? Because the computer is binary, the power of 2 is used to represent the equal number of colors.

The color channel here is not a concrete thing in concept.

We can compare the three primary colors of light to three dimmable desk lamps with different colors, and then the channel is equivalent to the dimming button.

For viewers, what they feel is only the image itself, and they don't think about how the three colors are mixed.

Just like in the movie, you only care about the performance of the actors and don't consider the process of the director when shooting.

Therefore, the function of the channel is "control" rather than "display".

You can use the letters R, G and B plus their respective numerical values to represent colors, such as R32, G 157, B95 or r32g 157b95.

Sometimes, in order to save trouble, the letters 32, 157, 95 are omitted (separated symbols cannot be marked wrong). Then the order of representation is RGB.

There is also an expression of 16, which will be mentioned later. That is not important.

So how do these numbers correspond to colors, or how can we tell what colors they are from a set of numbers?

In fact, it is difficult for beginners and even veterans to judge colors directly from numerical values.

Because we have to consider the mixing of three colors of light, which requires some experience.

But this ability is not necessary. Even if it can't be done, it won't hinder the future.

For a single r or g or b, when the value is 0, it means that the color does not emit light; If it is 255, the color is the brightest.

It's like dimming a desk lamp. The number 0 is equivalent to turning off the lights, and the number 255 is equivalent to turning the dimming knob to the maximum.

RGB mode is the physical color mode of the display. This means:

No matter what color mode is used in the software, the image will eventually appear in RGB mode as long as it is displayed on the display.

Therefore, the operation in RGB mode is the fastest, because the computer does not need to handle additional color conversion work. Of course, this speed difference is hard to detect, just theoretical.

As long as the image is displayed on the computer screen, it must be in RGB mode. Because the physical structure of the display follows RGB.

CMYK, also known as printing color mode, is used for printing as its name implies.

Compared with RGB, it has a big difference:

RGB mode is a luminous color mode, and you can still see the contents on the screen in a dark room.

CMYK is a color mode that depends on reflection. How do we read the contents of the newspaper? It is sunlight or light that shines on the newspaper and then reflects into our eyes to see the content. It needs an external light source. If you are in a dark room, you can't read the newspaper.

As mentioned above, as long as the image displayed on the screen is expressed in RGB mode. Now add: As long as the images you see in printed matter, they are all expressed in CMYK mode. Such as periodicals, magazines, newspapers, posters, etc. They are all printed, so they are in CMYK mode. Similar to RGB, CMY is the initials of three printing inks: cyan, magenta and yellow.

K takes the last letter of black, and the reason why it doesn't take the first letter is to avoid confusion with blue.

Theoretically speaking, only three kinds of CMY inks are enough, and these three kinds together should turn black.

However, due to the current manufacturing process can not produce high-purity ink, the result of CMY addition is actually a dark red. So you need to add special black ink to neutralize it.

The grayscale image of CMYK channel is similar to RGB, which is the expression form of content. RGB gray scale indicates color brightness, and CMYK gray scale indicates ink concentration. But they have different definitions of light and shade in gray-scale images:

In RGB channel grayscale images, whiter means higher brightness, and blacker means lower brightness. Pure white indicates the highest brightness, and pure black indicates zero brightness.

In the grayscale image of CMYK channel, whiter means lower ink content, blacker means higher ink content, and pure white means no ink at all. Pure black indicates the highest ink concentration.

When the images are delivered for printing, it is generally necessary to make the gray-scale images of these four channels into film (called film), and then make sulfuric acid paper. , and then print it on the printer. The traditional printing machine has four printing cylinders (figuratively speaking, the actual situation is different), which are responsible for printing cyan, magenta, yellow and black respectively. A piece of white paper is printed four times after entering the printing machine, first the cyan part of the image, then the magenta, yellow and black parts.

From the above sequence, you can clearly feel the effect of adding various inks.

In the printing process, the paper is transported between rollers, and may be displaced due to thermal expansion and contraction or other reasons, so that the place where the color should be printed cannot be printed. In order to check the quality of printed matter, when printing various colors, a+symbol will be printed in the blank space of the paper. If each color overprint is correct, you will only see a+symbol on the final product. If there are two or three, it means that there is a misregister, which will cause waste products.

Printing materials with different uses have different waste standards due to overprinter errors. Low-quality printed materials such as newspapers are allowed to have an error of 0.5 mm or even+0/mm. For picture books, exquisite magazines, especially maps and other waste products, the standards are much stricter.

So what color mode is the inkjet printer used by our ordinary family? Will there be overprint error?

As mentioned earlier, as long as the printed matter is in CMYK mode, so is the inkjet printer, which at least contains four-color ink cartridges of CMYK (individual models will be more), similar to the printer.

However, inkjet printers will not produce overprint errors. Why?

We say that the paper of the printing machine has to go in and out of four rollers, and there is a misregister between this entry and exit. While inkjet printers print at one time. So there is no overprint error.

So how does the inkjet printer realize one-time printing? In an inkjet printer, a plurality of nozzles are arranged one after the other.

When printing in this way, the first line of paper is sprayed with C, and then the paper moves forward by one line. The original first line stops under the M nozzle and sprays M color, while the new blank second line sprays C color.

Then the paper moves forward again, and the lines that have been sprayed with C and M now stop under the Y nozzle and are sprayed with Y color. The second line is sprayed with m. The new blank line is sprayed with c. And so on.

Since the principle of inkjet printer is not complicated, why don't large printers use this printing method?

Because this printing method is very slow, the nozzle needs to have a moving process in each line, which takes time, and it takes longer if the large format paper is used. However, a large number of printed materials such as newspapers need to be completed in a short time, and this printing method is powerless. And the accuracy is not as good as that of a printing machine.

So there is a big difference between printing and printing. Generally, the printing volume is very small, and the requirements for quality and speed are not high. Commonly used in individuals and small offices. Printing is the opposite. With the progress of printing technology, many small and medium-sized printing plants now adopt four-color printing, which reduces the rejection rate.