Why must I convert the RGB mode to the CMYK mode before printing?

Source: Internet
Author: User
Tags color gamut

Turn: http://nyza.blog.163.com/blog/static/44463822200781284712853/

1. What is image resolution? Why emphasize it?
A: A high-resolution image contains more pixels than a low-resolution image of the same size. The image information is also large, and the presentation details are clearer, this is one reason to consider the output factor to determine the image resolution. If an image is used for display on the screen, the resolution is 72 pixels/inch. If the image is used for output by a 600dpi printer, the resolution is 150 pixels/inch; to print the image, it must be 300 pixels/inch in high resolution. The image resolution setting should be appropriate: if the resolution is too high, the operation speed is slow and the disk space is occupied is large. If the resolution is too low, the image details are expressed, cannot meet the corresponding quality requirements.

2. Why image file formats are required for images? There are several formats of pre-printing image files. What are their respective properties?
A: image file formats determine how files are compatible with various application software and how files exchange data with other files. Because there are many image formats, you should decide the format of the Image Based on the purpose of the image.
Commonly used image file formats include:
Tiff format: tiff is a Tagged Image File used to store images composed of color channels. Its biggest advantage is that images are not restricted by operating platforms, it can be used on PCs, Mac machines, and Unix machines. It can save Alpha channels and store color separation data in a file. It is the most common image format for printed files.
EPS format: the EPS format is used for printing and printing. It can save duotone information, store Alpha channels, store paths, and add network information.
GIF is an 8-bit format that can only express 256-level colors. It is a common format for images transmitted over the Internet and is generally not used for printing.
PSD is used as an intermediate transition of an image file to save the channel and layer of the image for later modification. This format has poor connectivity. Only Photoshop can use it. Few other applications support it and cannot directly use it for printed output.
Jpe is not only a file format, but also a compression method. This compression is lossy and may vary in the size of the loss. Some small files cannot be identified by the human eye and cannot be directly used for printed output.

3. What is printing color?
A: The printing color is composed of different percentages of C (green), m (red), y (yellow), and K (black). Therefore, the color mixing is more reasonable. C, M, y, and K are the four primary colors used for printing. During printing, these four colors all have their own color editions, which record the outlets of these colors, the four colors are combined to form the defined primary colors. In fact, the four printing color outlets on the paper are separated, but the distance is very close. Due to our limited ability to distinguish eyes, we cannot distinguish them. The visual impression we get is the mixed effect of various colors, which produces different primary colors.
Y, M, C can synthesize almost all colors, but still need black, because the Black produced by Y, M, C is not pure, in the printing should be more pure black.
The electronic files used for printing must be four-color files (C, M, Y, k). Files in RGB color mode cannot be used for printing and output. Remember !!

4. What is color separation? Is color separation so important? How to separate colors in Photoshop?
A: color separation is a term used for printing. It refers to the four primary colors of the original article, namely, yellow, magenta, blue, and black; in computer printing design or graphic design image software, color separation is to convert the color mode of scanned images or images from other sources to CMYK mode.
Generally, scanned images are in RGB mode, and images taken by digital cameras are in RGB mode. Most images downloaded from the Internet are in RGB color mode. If you want to print, you must divide the color into four colors: yellow, red, blue, and black. This is the requirement of printing. If the image color mode is RGB or lab, the output may only have outlets on the K version, that is, when rip is interpreted, only the color information of the image is interpreted as gray.
In Photoshop, the color separation operation is actually very simple: you only need to convert the image color mode from RGB mode or lab mode to CMYK mode. In this way, the color of the image is represented by the color material (ink), with four channels of color. When the image is output, the dot is generated based on the color channel data and divided into porn, magenta, blue, and black.

5. During color separation, when the image is switched from RGB to CMYK, some colors on the screen will change significantly. Why? What is the impact on image color?
A: When the image is converted from the RGB color mode to the CMYK color mode, some bright colors on the image will change significantly. This change can be observed obviously sometimes, it usually changes from bright colors To Darker colors. This is because the color gamut of RGB is larger than that of CMYK, that is, some colors that can be expressed in RGB color mode are beyond the color range that CMYK can express after being converted to CMYK, these colors can only be replaced by similar colors. As a result, these colors have changed significantly. When creating an electronic file for printing, we recommend that you set the initial file to the CMYK mode to avoid the use of RGB color mode, so as to avoid Color Deviation during the color separation conversion.

6. What is the better color pattern of the image?
A: In Photoshop, the color modes of images include RGB, CMYK, grayscale, and other color modes. The final purpose of the image design depends on the pattern used to design the image. If the design image is to be printed or printed, the best color uses the CMYK color mode, so that the color displayed on the screen is close to the output color or printed color. If the image is gray, the grayscale mode is better, because even if the image is expressed in CMYK color mode, it still looks Neutral gray color, but its disk space is much larger. In addition, if the gray image is to be printed, for example, in CMYK mode, there are four versions for printing and printing. if the cost is not high, it may also cause the problem of partial color when the gray balance is not properly controlled, when the amount of printing ink is too large, the gray image will produce a color bias. If it is designed for electronic media display (such as web pages, computer projections, video recordings, etc.), it is best to use the RGB mode for the color mode of the image, because the RGB mode is more colorful and richer, the screen looks better. In addition, there are only three image channels, with a smaller data volume and less disk space.

7. What is special color and special color printing?
A: special colors refer to the four-color synthesis of C, M, y, and K during printing. Instead, special ink is used to print the color. The special color ink is pre-mixed by the printing factory or manufactured by the Ink factory. For each special color of a print, a special color version is available during printing. Use special colors to make colors more accurate. Although the color cannot be accurately expressed on the computer, the accurate color of the color on the paper can be seen through the pre-printed color card of the Standard Color Matching System, for example, the Pantone color matching system creates a detailed color sample card.
For the non-standard special colors set in the design, the printing factory may not be able to accurately allocate them, and the accurate colors cannot be seen on the screen, therefore, do not use the custom colors unless otherwise required.

8. How are gold and silver printed? What are the requirements of the pre-press design?
A: In the design, customers often require the use of gold and silver printing. Because gold and silver cannot be achieved by four colors, their printing and technology have special requirements. When printing, gold and silver are processed by special colors, that is, the use of Gold ink and silver ink to print, so the film should also be a special color, a separate film, and a separate print.
In computer design, a color should be defined to indicate gold or silver, and its color type should be defined as special color to meet the design requirements. Because silver and silver are not transparent, you can set them to overpint during design ).

9. What is bleeding? Why do we need bleeding?
For any image that exceeds the cropping line, a certain margin (generally 3mm) must be set aside outside the cropping line so that there can be a trace of inaccurate versions during trimming and cutting, this margin is called bleeding.

10. What is the printing process?
Work in the early stage of printing generally refers to photography, design, production, layout, and film publishing;
Work in the middle of printing, printing finished products through the printing press.
Film (philin) cannot be directly used for printing. The color Edition used for printing is usually called the PS edition. It is an aluminum metal edition with a medicated film on one side. Film is used to determine the film in the color when exposed. The specific operation is as follows: cover the film with a medicated film on the Color board, expose it under the purple light, and make the film completely transparent. The color board will be completely illuminated by the purple light, the pharmaceutical film is completely decomposed, and the film contains images or text. Because it is not transparent or not completely transparent, the pharmaceutical film on the color version will not be decomposed or not completely decomposed, the decomposed pharmaceutical films will be cleaned, so that the images on the films will be completely transferred to the color version.
In the printing, the color of the film where there will be adsorption ink, with the pharmaceutical film density, the amount of adsorption ink is not the same, so there is a different color depth.
The paper is colored in four colors, C, M, y, and K, and various colors are displayed.
Post-printing work generally refers to post-processing of printed matter, including cutting, film, die-cutting, binding, mounting, etc. It is mostly used for propaganda and packaging printed matter.

11. What fonts should I use when making printed electronic files?
If the file is formatted using strorar or CorelDraw, the font is not involved. Because all the text in the file must be converted to a vector graph (that is, a contour is created) and must be converted to a vector graph. Otherwise, the output will cause the text to run.

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