1. When making a plate, the original should be divided into cyan (C), magenta (M), yellow (Y), and black (K). What is the principle of color separation?
Answer: There are tens of thousands of colors on a color artwork or color photo. It is almost impossible to print these tens of thousands of colors one by one. The printing method is four-color printing. That is, the color of the original is decomposed into four color plates of cyan (C), magenta (M), yellow (Y), and black (K), and then the colors are combined during printing. The so-called "color separation" is based on the principle of the subtractive color method, using the red, green, and blue color filters to selectively absorb the color light of different wavelengths, and the original is decomposed into three primary colors of yellow, magenta, and cyan. In the color separation process, the color light absorbed by the color filter is the complementary color light of the color filter itself, so that a negative film of black and white images is formed on the photosensitive film, and then screened to form a dot negative film, and finally copied and dried into various colors Printing plate. This is the earliest principle of photographic color separation.
Due to the development of printing technology, we can now separate, sample and convert the color of the original color into digital information through the pre-press scanning equipment, that is, use the same method as the photoengraving to decompose the original color into red (R), green (G), Blue (B) three colors, and digitize, and then use the computer to mathematically decompose the digital information into cyan (C), magenta (M), yellow (Y), black (K) four-color information.
2. Why should the screen be printed before printing?
A: Because the printing process determines that printing can only use dots to reproduce the continuous level of the original. If you zoom in, you will find that it is composed of countless dots of different sizes. We see that although the dot sizes are different, they all occupy the same size of space. This is because after the original image is screened, the image is divided into countless regularly arranged dots, that is, the continuous image information is turned into discrete dots Image information. The larger the dot, the darker the color and the darker the level; the smaller the dot, the lighter the color and the brighter the level. The size of the fixed space occupied by each dot is determined by the number of screens. For example, if the mesh size is 150lpi, there are 150 dots in one inch of length or width. The location of the dot space and the dot size are two different concepts. For example, C50% represents the meaning that the dot size accounts for 50% of the dot space position, and 100% means that the dot size completely covers the dot space position, which is called in the printing. "On the ground", 0%, because there is no dot, only the spatial location of the dot, so no ink is printed on this place. Obviously, the larger the number of linked meshes, the smaller the space occupied by the dots, and the more levels of detail that can be described. In fact, the layers and colors of the original are reproduced by this method of hanging the net.
3. What is process color?
Answer: Process color is a color composed of different percentages of C, M, Y, and K, so it is more reasonable to call it a mixed color. C, M, Y, K are the four primary colors commonly used in printing. When printing primary colors, these four colors have their own color plates. The dots of this color are recorded on the color plates. These dots are generated by the halftone screen, and the four color plates are formed together. The primary colors defined. Other primary colors can be formed by adjusting the size and spacing of color dots on the Internet. In fact, the four printing colors on the paper are separated, but they are very close. Due to the limited resolution of our eyes, they cannot be distinguished. The visual impression we get is the mixed effect of various colors, so a variety of primary colors are produced.
Y, M, C can synthesize almost all colors, but black is also required, because the black produced by Y, M, C is impure, and a more pure black is required when printing, and if Y, M, C is used There will be too much local ink in black.
4. What are the equipment of the color desktop publishing system? What are the software?
Answer: The color desktop publishing system is composed of three parts: the image input part, the image processing part, and the image output part. The specific components of each part are as follows:
(1) Part of the equipment for image input: scanner, digital camera, computer. Software: device driver software, and operating system of MAC and PC.
(2) Part of the equipment for graphic processing: computer. Software: 1. Computer software: Image processing software is Photoshop and Painter. 2. Graphics software: FreeHand, CorelDraw. 3. The typesetting software is PageMaker, QuarkXpress. 3D image creation software: 3DS, Infihi-D, Strate-StudioPRO.
(3) Some graphic output devices: computers, color printers, laser printers, laser imagesetters, direct plate-making machines, plate-making machines, etc., direct digital printing machines. Software: RIP, driver software, font library.
5. Why do computer design systems need to use large-capacity memory? What are the commonly used mass storage?
Answer: Many photos or computer-generated images are used in the design. Because of the needs of print output, the resolution of the image is usually higher, about 300Dpi. Therefore, the disk space occupied by the image is very large. For example, for a 4K imposition file, generally all stored files should exceed 100M. The commonly used 3.5-inch floppy disk can not meet the requirements of storing images, so a large-capacity memory is used. Commonly used large-capacity memory are: â‘ Magneto-optical disk (MO) drive, the disc has 230M and 460M or larger. â‘¡ Active hard disk. â‘¢ZIP (100M) driver. â‘£ CD rewritable.
6. What are the workflows for prepress design or computer design?
A: The general workflow has the following basic processes:
①Clear design and printing requirements, accept customer information ② Design: including input text, images, creativity, imposition ③ Black and white or color proofs, allow customers to modify ④ Revise according to proofs ⑤ Re-publish proofs, let customers modify until Finalization ⑥ Let the customer sign out the film ⑦ Pre-press proofing ⑧ Send the printing proof to let the client see if there is a problem, if there is no problem, let the client sign. All the pre-press design work will be completed. If there are problems in the proofing, you have to modify and re-export the film.
7. What is the workflow of the computer design system to complete the design?
Answer: The workflow in the design system is as follows: â‘ First, scan the original according to the final size of the image, and adjust the image in the image software, and at the same time, you can complete some creative design work.
â‘¡ Typesetting design work in graphics or typesetting software: including entering text, drawing graphics, and placing images.
â‘¢ After the customer finalizes, send the file to the output center to output the film. The laser imagesetter works in PostScript language, and the layout is described as a dot matrix image by RIP (raster image processor), and is divided into four colors of C (cyan), M (magenta), Y (yellow), and K (black) sheet. If the final requirement of the design is not to output film, but to a large-scale color inkjet sample, it can be output by an inkjet machine.
8. What is density?
Answer: The light phenomenon of color objects generally includes transmission, reflection and selective absorption. As shown in Figure 3-20 (color), O is a color object. When the light energy of the incident light is Q, it is selectively absorbed by the object O. The light energy transmitted or reflected is Q out. Then the density of the object O is: D = lg (Q out / Q in) so the density represents the nature of the amount of light absorbed by the object. Objects that absorb a large amount of light have a high density: objects that absorb a small amount of light have a low density. Density is a commonly used physical quantity in the printing industry to measure the light transmittance of film and the color depth of printed matter. Greater China Graphic Arts Network
9. How to choose the correct output angle?
A: In order to avoid hitting the net, in theory, there should be a difference of 22.5 degrees between the colors, but practice has proved that the four angles of 15 degrees, 45 degrees, 75 degrees and 90 degrees are very effective. The yellow version stimulates vision It is relatively weak and has poor visual sensitivity, so it is generally set at 90 degrees, and vision is most sensitive to a 45-degree angle. Generally, the main color of the original document is magenta or cyan at 45 degrees. For example: for the blue sky and white clouds, the blue version should be set to 45 degrees, for the morning glow and the sunset, the magenta version should be set to 45 degrees, and the non-45 degree angle of magenta and cyan can be set. It is 15 degrees, and the black version is set at 75 degrees.
10. After the file is output, only the black version has corner lines, other versions do not have corner lines, what should I do?
Answer: The only way is to re-output, and to change the color of the corner line from 100% BK to 100% C100% M100% Y100% BK, that is, to change the monochrome black to four-color black.
11. What should I do if the color version is not correct with the original color version?
Answer: Re-output all the color versions. Although this is the most stupid way, it is the most safe way.
12. When outputting film, is it better to select the medicine film face up or down? What is the difference?
When outputting the film, whether the drug film is selected to face up or down depends on whether the film is positive or negative. When the film is taken out, choose the medicine film face up or down to get the anti-positive film. When the negative film is out, choose the medicine film face up to get the positive film. Because for the positive film, the film can be directly printed, and the film surface is just in contact with the PS version, and the effect of the printing is good. For the negative film, it must be copied into a positive film before printing. When copying, the negative film is placed on the copy table with the drug film facing up, and the copy film is stacked on top, so that the copy film also just touches the surface of the drug film. To ensure copy quality. In the process of printing and copying, the light source does not directly illuminate the surface of the drug film.
13. What is the laser value? How to adjust?
Answer: The laser value refers to the exposure of the phototypesetting laser. It not only determines the size of the film on-site density and whether the dot value of the software display matches the output dot value of the imagesetter, but also is closely related to the life of the laser. (Temperature and time) Under relatively fixed conditions, the film solid density D real ≥ 4.0, when the measured 50% dot percentage is greater than 52%, the laser value can be appropriately reduced; when the measured 50% dot percentage is less than 48%, The laser value can be increased appropriately, and the range of increasing and decreasing the laser value should make the 50% dot percentage error within ± 2%. Similarly, when D is less than 4.0, when the measured dot value at 50% is greater than 52%, the laser value should be appropriately reduced. When the dot value at 50% is less than 48%, the laser value should be appropriately increased . The laser exposure of different types of film will be different, so every time the type of film is changed, the laser value should be re-tested. When the development, fixing and film are fixed, the laser exposure is also fixed, and there are some that do not meet the requirements. The place can be adjusted by film linearization.
14. What is image resolution? Why emphasize it?
A: The resolution of the printed image has been introduced in the basic part of printing. We know that a high-resolution image contains more pixels than a low-resolution image of the same size, more image information, and clearer performance details, which is One reason to determine the image resolution considering the output factors. Since the uses of the images vary, the resolution should be determined according to the uses of the images. If an image is used for display on the screen, the resolution is 72Dpi or 96Dpi; if it is used for 600Dpi printer output, an image resolution of 150Dpi is required; for printing, a high resolution of 300Dpi is required. Row. The image resolution setting should be appropriate: if the resolution is too high, the running speed is slow and the disk space occupied is large, which does not meet the principle of high efficiency; if the resolution is too low, it will affect the expression of image details and does not meet the principle of high quality. Greater China Graphic Arts Network
15. Why do images need to have an image file format? There are several image file formats often involved in prepress, and what is their nature?
A: The image file format determines what type of information should be stored in the file, how the file is compatible with various application software, and how the file exchanges data with other files. Since there are many image formats, you should decide what format the image should be stored according to the purpose of the image.
The image file formats commonly used in design are:
TIFF format: TIFF is a labeled image file used to store images composed of color channels. Its biggest advantage is that the image is not limited by the operating platform. It can be used regardless of PC, MAC or UNIX. It can save the Alpha channel and can store color separation data in a file.
EPS format: EPS format is used for printing and printing, can save Duotone information, can store Alpha channel, can store path and screen information.
GIF is an 8-bit format that can only express 256 levels of color. It is a common format for spreading images on the Internet.
PSD is mainly used as an intermediate transition of the image file to save the channel and layer of the image for later modification. The format is poorly versatile, and only Photoshop can use it, and few other applications support it.
JPE is both a file format and a compression method. This compression is lossy, the loss size varies, and some are too small to be recognized by the human eye.
16. What is the number of printed images plus screen lines? What is the relationship between image resolution, scanning resolution, and output resolution of laser imagesetter?
Answer: Since the printed matter is composed of dots, the number of printed images plus screen lines refers to the number of screen lines per inch of the printed matter in the horizontal or vertical direction, that is, the number of hanging screen lines. It is called the number of screen lines because the earliest printed dots are wired. The unit of the number of hanging lines is Line / Inch (Line / Inch), referred to as LPI. For example, 150Lpi means that there are 150 network cables per inch. When adding images to the screen, the larger the number of meshes and the more the number of nets, the denser the dots and the richer the expressiveness of the layers.
Because the computer image is dot matrix, which is composed of pixels (the smallest unit of the image is called pixels). Image resolution can be visually understood as how many pixels describe a line in unit length in the horizontal or vertical direction. The more pixels used to describe this line, the higher the resolution. The unit of image resolution is generally Pixels
PerInch (pixels / inch), usually expressed in English as PPI. For example, the resolution of an image is 300PPI, which means that it has 300 pixels per inch in the horizontal or vertical direction; the resolution of an image is 720I, which means that it has 72 pixels per inch in the horizontal or vertical direction.
The resolution of some devices is similar to the resolution of images, except that they are expressed in points, so they are expressed as Dot Per Inch, or DPI for short. For example, the image input accuracy of an image scanner with a resolution of 1200 DPI is 1200 points or pixels per inch. The graphic output precision of the 3600DPI laser imagesetter is 3600 laser points per inch.
The image resolution PPI and the printing resolution LPI (screening line number) are both related and different: the image resolution is higher than the printing resolution, generally 2 × 2 or more pixels generate 1 dot, that is, LPI is DPI About one-half.
17. What are the types of scanners?
Answer: â‘ Roller scanner: divided into high-end drum scanner and small desktop drum scanner.
â‘¡Flatbed scanner: divided into three grades: high, medium and low. As the printing design, high and medium grade scanners should be selected.
â‘¢Handheld scanner, used in office etc.
â‘£Film and transparent media scanner. Used to digitize 35mm positive and negative films. Greater China Graphic Arts Network
18. What are the commonly used output devices? What are the fields of application?
Answer: The electronic files of the designed pages can be output using the following equipment:
1. Black and white laser printer: used to print black and white proofs or final black and white formal manuscripts.
2. Color laser printer: used to print color effect drafts or final color official drafts.
3. Color inkjet printer: used to print color effect drafts.
4. Large color inkjet printer: used to print large-scale color effects or final color official draft.
5. Digital proofer: used to check the content and color effect of the page.
6. Laser imagesetter: used to output film for printing.
7. Direct plate-making machine: used to output printing plates.
8. Digital printing press: prints are output directly from electronic pages. There is no need for film and printing plates.
19. What are the types of scanners? What's the difference?
A: There are two major types of scanners: one is the drum scanner; the other is the flatbed scanner, which can be divided into high-end professional scanners and low-end flatbed scanners. The roller scanner is developed from an electronic color separation machine, and its sensing technology is a photomultiplier tube. Figure 5-1 is a working principle diagram of the roller scanner. The flatbed scanner is scanned by the CCD device. Their different working principles determine the difference in performance between the two scanners:
(1) The highest density range is different: the highest density of the drum scanner can reach 4.0, while the general low-end flatbed scanner is only about 3.0. Therefore, the roller scanner can scan out more details in dark places and improve the contrast of the image.
(2) The image clarity is different: the drum scanner has four photomultiplier tubes: three are used for color separation (red, green, and blue), and the other is used for the virtual light mask. It can make unclear objects clearer and improve the clarity of the image, but the CCD does not have the function of this main surface.
(3) The degree of fineness of the image is different: after the image scanned by the photomultiplier tube is output and printed, its details are clear, the dots are delicate, and the texture is small, and the quality of the photo scanned by the flatbed scanner is relatively poor in terms of the fineness of the image some.
20. What is Pantone color? Why use Pantone color to set the color?
A: Pantone is a well-known ink brand in the United States and has become a standard for printing colors. It has made all the inks produced by it into chromatograms and color scales. Pantone's color scales have therefore become a recognized language for color communication. Users need a certain color, and they just need to calibrate by color scale. Due to the widespread use of Pantone color standards, computer design software has a Pantone color library and uses it for color definition. When using the Pantone color library to set the color, select the definition method as Pantone color, but it should be noted that most Pantone colors are spot colors. If you want to reproduce it with four colors, you should set the color type to the primary color. Figure 1-13 is an interface to define Pantone color.
21. What is color separation? Is color separation so important? How to separate colors in Photoshop?
Answer: Color separation is a printing term. It refers to the decomposition of various colors on the manuscript into four primary colors of yellow, magenta, cyan, and black; in computer printing design or graphic design image software, color separation works It is to convert the color mode of the scanned image or other source images to CMYK mode.
Generally, the scanned image is in RGB mode, and the image taken with a digital camera is also in RGB mode. Most of the pictures downloaded from the Internet are also in RGB color mode. If you want to print, it must be separated into four colors: yellow, magenta, cyan, and black. This is the requirement of printing. If the image color mode is RGB or Lab, there may be only dots on the K version when outputting, that is, the RIP interpretation only interprets the color information of the image as gray.
In Photoshop, the color separation operation is actually very simple: just change the image color mode from RGB mode or Lab mode to CMYK mode. The specific operation is to execute Image / Mode / CMYK. In this way, the color of the image is represented by the color material (ink), with 4 color channels. When outputting the film, the image will generate dots according to the color channel data, and be divided into four color separation film pieces of yellow, magenta, cyan, and black.
22. During color separation, when the image changes from RGB to CMYK, the naked eye can see that some colors on the screen will have obvious changes. What is the reason? What effect does it have on the color of the image?
Answer: When the image is changed from RGB color mode to CMYK color mode, some bright colors on some images will have obvious changes. Such changes can sometimes be clearly observed, and generally change from bright colors to darker. Some colors. This is because the color gamut of RGB is larger than that of CMYK, which means that some colors that can be expressed in RGB color mode are beyond the range of colors that CMYK can express after being converted to CMYK. These colors can only be Use similar colors instead. So these colors have produced more obvious changes. In fact, if any color in the RGB color mode image exceeds the color gamut, it can be previewed with Gamut Warning.
23. What is the color gamut space? What's the point of figuring out the color gamut space?
We edit images in RGB, CMYK and Lab. The essential difference is that they work in different color gamut spaces. Color gamut refers to the range of colors that can be expressed by a certain color expression mode, and also refers to the color range that can be expressed by specific media such as screen display, printer output, and printing and copying. The colors of the visible spectrum in nature constitute the largest color gamut space, which contains all the colors that the human eye can see. In the color mode, Lab color gamut space is the largest, it contains all the colors in RGB, CMYK.
24. Which mode is better for the color mode of the design image?
A: In Photoshop, the color modes of the image are RGB mode, CMYK mode, GrayScale mode, and other color modes. Whichever mode is adopted for the design image mode depends on the final use of the design image. If the designed image is to be printed or printed on printing paper, it is best to use CMYK color mode for color, so that the color seen on the screen is close to the output print color or printed color. If the design is used for electronic media display (such as web pages, computer projection, video, etc.), the RGB color mode of the image is best, because the RGB mode color is more vivid and richer, and the picture is better. And there are only three channels of images, the data volume is smaller, and it takes up less disk space. If the image is gray, it is better to use GrayScale mode, because even if the image is expressed in RGB or 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, such as the CMYK mode, there are 4 versions when printing out the film and printing. The cost is not to mention, and it may also cause the color shift problem when the gray balance is not well controlled during printing. When the amount of ink is too large, the gray image will have a color cast.
25. How are gold and silver printed? What are the requirements for prepress design?
Answer: In the design, customers often require the use of gold and silver printing. Since gold and silver cannot be realized by four-color printing, their printing and technology have special requirements. When printing, gold and silver are processed according to spot colors, that is, they are printed with gold ink and silver ink, so the film should also be a spot color film, and a film is produced separately and printed separately.
In computer design, a color should be defined to represent gold and silver, and the color type should be defined as a spot color to meet the design requirements. Since gold, silver and silver are opaque, the design of gold and silver can be set to Overpint.
26. What is spot color and spot color printing?
Answer: Spot color refers to the printing of this color instead of synthesizing this color by printing four colors of C, M, Y, and K, but by printing the color with a specific ink. Spot inks are pre-mixed by printing plants or produced by ink plants. For each spot color of the printed matter, there is a special color version corresponding to it when printing. Use spot colors to make colors more accurate. Although the color cannot be accurately represented on the computer, you can see the exact color of the color on the paper through the pre-printed color sample card of the standard color matching system. For example, the Pantone color matching system creates a very detailed color sample card .
For the non-standard spot colors set in the design, the printing house may not be accurately allocated, and the accurate colors cannot be seen on the screen, so if it is not special needs, do not easily use the spot colors you define.
27. What are the commonly used color expression methods in computer performances? In general, what method is better to define color?
A: Whether it is on a computer or when printing, you need a way to describe different colors. In chromology, the method of expressing colors is also called color model or color mode. There are many types of color models, each of which can describe colors from different angles, but different color modes are suitable for different occasions, and the accuracy is different.
Computer color mode
1. RGB mode: also known as RGB color space. It is a colored light table color mode, it is widely used in our lives, such as televisions, computer displays, slides, etc. are all using light to express color. Scanning images is often required in printing and publishing. The first thing the scanner extracts when scanning is the RGB color information on the original image. The RGB mode is an additive color mode, and any color can be described by the radiation of R, G, and B. When the computer defines colors, the values ​​of the three components R, G, and B are in the range of 0-255. 0 means no stimulation, and 255 means the stimulation reaches the maximum value. When R, G, and B are all 255, white light is synthesized, and when R, G, and B are all 0, black is formed. This mode is often used when displaying color definitions on the display. If the image is used for TV, slide, network, multimedia, RGB mode is generally used.
2. CMYK mode: also known as CMYK color space. For those engaged in the printing industry, CMYK is the most familiar. This mode is a subtractive color model, following the subtractive color mixing law. The CMYK mode essentially refers to the size of C, M, Y, and K dots printed when reproducing colors, so the value range of C, M, Y, and K is 0% -100%. CO% MO% YO% KO% means white, C100% M100% Y100% K100% means black.
3. HSB mode: HUE, Saturation, Brightness mode.
28. Since RGB images display better than CMYK images and have more beautiful colors, can RGB images be output directly? What are the consequences of doing this?
A: Because the color gamut of RGB is larger than CMYK, some colors are displayed on the screen, but the four-color inks are not printed as expected. To know the consequences, just give it a try. Due to the difference in RIP, the RGB image may only have the image on the black version on the color separation film, and no image on the other color versions, or it may be that the information (dots) of the picture on the four-color film is exactly the same, that is, the equivalent grayscale image Although some development software or RIP can convert RGB to CMYK, it is best to use scanning software or Photoshop for mode conversion.
29. Save the color image in DCS format, there are images when printing black and white, but there is no image on the output film. Why is that?
Answer: storing the picture in the second half of the DCS format will produce five files,
30. What is RIP? Why do you like to use software RIP now?
Answer: RIP is the abbreviation of RasterProcessing, which refers to the software or hardware card in the phototypesetting system that interprets PostScript encoding as a dot matrix image, which is generally called a raster image processor. It plays an important role in the color publishing system. Its function is to quickly interpret the finished page as a command that can control the dot matrix output of the laser recorder. It can automatically convert text, graphics, images and other elements on the page. Into digital dot matrix information, and then use the information to control the output device to record, so that its work is "off" or "on".
The replacement of hardware RIP requires complex technology and a long time, and it cannot adapt to the rapid development of software technology; while software RIP is widely used for its advantages of fast update, high processing quality, high speed, and display of processed results. And a software RIP can drive multiple imagesetter at the same time, the network function is strong.
31. Why not set the resolution in typesetting and graphics software?
Answer: The typesetting graphics software is object-oriented software. The representation of text and graphics is expressed in algorithmic language. The objects produced are not related to resolution. They are output at the resolution of the output device when they are output. Yes, if the output device has a high resolution, the graphic output resolution of the page will be high. Therefore, graphics software and typesetting software do not need to set the resolution. When importing images in layout and graphics software, it is necessary to read the dot matrix information of the original image, which is related to the resolution of the original image.
32. How many types of text in CorelDraw?
A: CorelDraw divides text into two different types, one is artistic text and the other is paragraph text. Although these two types of text are created using text tools, they have different characteristics. With the characteristics of more graphic objects, more special effects can be applied to artistic text; paragraph text can use more text format. Based on the different characteristics of these two types of text, they can be used for different purposes. If you only need to use a small amount of text or apply more formatting to the text, such as short titles and descriptions, you can use artistic text; if Need to deal with a large amount of text and apply more formatting, such as newspapers, brochures, etc., you can use paragraph text.
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