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Home Blogs & News Blogs Customer Case Story Learn More About CMYK & RGB In Packaging

Learn More About CMYK & RGB In Packaging

  • October 30, 2020
As people have a new understanding of color itself and more applications, color slowly in different media presents a variety of changes. But in fact, the color displayed on the electronic screen can not be fully rendered on paper printing, because the two color modes are essentially different, RGB (color light -- as many as tens of thousands of colors on the screen) and CMYK (color ink -- as ink -- as printing four colors) .

Do you want to know how the colorful colors appear on the paper?

CMYK is the most widely used color mode in printing, and is also the overlapping printing system used in four-color division. It refers to the use of cyan, magenta, yellow and black four-color ink overprint to render color. When the completion of a work of design, do a good pre-press preparation and understand the principles of CMYK printing is crucial. Next Small Series will take you to experience CMYK colorful printing world!


Introduction to four-color printing

What’s CMYK?

Through the visible spectrum (as shown above) and the study of color, the theory of pure black is completely absorb light, and pure white is completely reflective. When sunlight strikes an object, the object will absorb some of the light and reflect the rest of the light. The color of the reflected light is the color of the object we see, that is, filtering out unwanted color from the white light, leave the desired color, which is a subtractive color pattern. Subtractive mode is used not only for the color of visible objects, but also for the color rendering of paper printing.

According to this model, modern printing on the evolution of the CMYK color model, as shown in the picture above. Because CMYK can present the color of this world to the maximum extent, it is also called printing color mode. It uses the principle of three primary colors of pigments, plus black ink, a total of four colors mixed and superimposed, forming the so-called “full-color printing” , which is currently the most widely used in the printing industry a color display.

CMYK stands for:

C (Cyan) = Teal

Magenta = Carmine

Y (Yellow) = Yellow

K (Black) = Black

In practical application, C, M, y three printing primary colors can not be superimposed to blend out of true black, dark brown is the limit of their harmony. But in the printed matter, the use of black is very high frequency, so that the introduction of black (K) . In addition to being used alone, it can be mixed with other primary colors to enhance the dark tone and deepen the dark part of the color level.

If the printing effect of single black K100 is not black enough, consider combination of K100 and C30 or combination of K100, C50 and M50, these two color combinations can get more black printing effect.

It shows a four-color printer schematic, a four-color printer photo, and a four-channel printing photo.

According to Information, in 1906, CMYK color model by The Eagle Printing Ink Company was first invented, has more than 100 years of history. They found that four colors, cyan, magenta, yellow and black, can be combined to produce most of the colors that the human eye can recognize, and the colors are bright and rich. When printing, the substrate in turn through the printing press four nano-imprint lithography drum, each drum use CMYK in a color of ink.

As a result of the printing plate is a dot, so when the ink is transferred to the substrate, the four colors overprinter together, can form a rich color graphics and text.

What is RGB? Why not print in RGB color mode?

Red, green and blue can be seen from different angles when water drops are on a computer or mobile phone screen. RGB namely color light three primary colors, mainly used in computers, projectors, smart phones and other display equipment. RGB belongs to add color mode, its color order range is 0 ~ 255, the larger the color is brighter, the smaller the color is darker. As a result, when the color value of red, green and blue is 255, it is white, and when the color value is 0, it is black.

Different from RGB, CMYK belongs to subtractive color mode, color value range is 0 ~ 100% . The larger the percentage, the darker the color; the smaller the percentage, the lighter the color. When all four colors are 100% Black, when all are 0 is white.

The essential difference between the two is that RGB is color light (screen) , and CMYK is color (ink) . Printing, and can not be displayed on the screen true color reproduction, so printing does not use RGB color mode, but use CMYK color mode.

Need to pay special attention to is: the print version of the design document, in the beginning should be set to CMYK color mode. If the design is designed in RGB mode, the document will be converted to CMYK mode after completion, the image will produce color difference, resulting in unsatisfactory printing results.

Color separation and plate making

In four-color printing, the printing document image or text color decomposition into C, M, y, k four-color plate, with the corresponding C, M, y, K four printing machine channel printing.

In the process of color separation, the color light absorbed by the filter is the complementary color light of the filter itself, so that the negative film of the black-and-white image is formed on the photographic film, and then screened to form dot negative, and finally copied and insolated into various color printing plates. This is the first photographic color separation principle.

In the process of color separation, plate-making for the perfect display of printing color is very important, especially in the drying of various color plates, plate-making will directly determine the type of screening used and dot size, shape, density and other parameters.

Before printing, color separation of the design document, according to Cyan, magenta, yellow and black produced four corresponding color plate. The earliest use of photographic color separation principle, the use of film plate, the final copy, drying of a variety of color plates.

With the development of printing technology, CTP (Computer to plate) imaging technology (Computer to plate) , which was developed gradually from the 1990s, has become more and more important, prepress scanning equipment can be used to color separation of the original, sampling and conversion into digital data. CTP plate-making automation makes plate-making fast and convenient, high efficiency, can directly output design documents into a printing plate, and dot reduction rate is high, computer-based plate-making precision, printing quality is also higher.


Am Dot and FM Dot

Am Dot
In the process of printing, the image must be changed into halftone image by screening in order to finish printing. In accordance with the screening method, Dot can be divided into AM DOT and FM Dot. Amplitude modulation dot is the most widely used dot, the size of the dot can be adjusted to display the image of light, dark and shallow levels, so as to achieve the color transition. The use of amplitude modulation Dot Seihan, you need to consider the size of the dot, shape, Angle, wire accuracy and other factors.

Fm Dot
As a new technology, the screening method with fixed dot size is used to control the density of Dot to show the depth of color and the light and dark levels. As the dot of the bright adjustment part is sparse, the DOT of the dark adjustment part is dense, and the dot of the FM dot does not have the problem of dot angle, therefore, when using the FM Dot to print, more than four-color printing plates can be made, and the original manuscript can be printed with a high degree of reduction, and does not need to consider in the printing process each color plate registration question. But FM DOT also exists the following shortcomings: Because DOT is small, in print,

printing is easy to lose the dot, resulting in the loss of image hierarchy, printing machine precision requirements, ink balance control is not easy to grasp, resulting in poor image quality.


Dot Factor
Dot shape
Dot shape refers to the geometry of a single dot, that is, the outline shape of the DOT. In addition to their own performance characteristics, different shapes of mesh points have different changes in the process of image reproduction, which will produce different reproduction results and affect the final printing quality.

Dot shapes are divided into square, round, diamond, oval, double-point type, etc. . In modern digital screening technology, more dot can be selected. In the case of 50% ink, the dot is shown by the shape of the main square, round and Diamond Three.

Dot size
Dot size is determined by the dot coverage, also known as the ink rate. The coverage rate of 0% of the network is called “off-grid” , the coverage rate of 100% of the network is called “Field” .

In the process of printing plate-making, there are two methods to identify the percentage of net coverage: one is to measure with densitometer, and then convert to the percentage of Dot area The other is to use a magnifying glass eyepiece dot area and blank area ratio, more intuitive, convenient, but also need experience. The percentage of identified nodes with coverage of less than 50% can be identified by the number of equivalent nodes that can be accommodated in the gap between the two opposite nodes.

Dot Angle

Dot Angle refers to the four-color mesh point of contact between the angle. In printing, it is important to use the correct dot angle. The Wrong Dot Angle can cause the print to produce a water-like moire, which can affect the image color rendering, resulting in poor visual effect. In four-color printing, four-color overlap after the maximum angle must be within 90 degrees.

So how do you arrange the angles between the four colors? Yellow is the lightest of the four colors and is therefore placed at the most visible angle, 0 or 90 degrees; Black is the darkest, at 45 degrees; Cyan and magenta are placed between yellow and black, cyan at 15 or 105 degrees and magenta at 75 degrees.

Number of screening lines
The number of screening lines is similar to the resolution, and the number of lines determines the fineness of the image. Generally, the more lines, the more exquisite printed products, but also with paper, ink and other materials have a greater relationship. A bitmap with a resolution of 300 pixels per inch is an image made up of 300 square pixels per inch. When the image is enlarged, it will be found to be composed of numerous dot. The printed image is made up of dots, so the number of dots in a printed image is the number of dots per Inch in the horizontal or vertical direction, in Line/Inch, or LPI. For example, 150 LPI means 150 lines per inch.

Common line count applications are as follows:

10 ~ 120 lines: suitable for low-quality printing, such as long-distance viewing of posters, advertisements, etc. .

150 lines: this precision is commonly used in ordinary four-colour printing.

175 ~ 200 lines: Used for fine picture books, pictorial newspapers, books and other printing.

250 ~ 300 lines: for the printing of picture books and books with high requirements.

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