Prepress Technology 30 Questions (15-18)

15. Why does the image need to have an image file format? There are several image file formats that are commonly involved in prepress. What are their natures?

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, the format of the image should be determined based on the use of the image.
The commonly used image file formats in the design are:

TIFF format: TIFF is a tagged image file used to save the image composed of color channels. Its biggest advantage is that the image is not limited by the operating platform. It can be used universally regardless of PC, MAC or UNIX. It can save alpha channels and can store separation data in a file.

EPS Format: The EPS format is used for printing and printing. Duotone information can be saved, Alpha channels can be stored, and path and screen information can be stored.

GIF is an 8-bit format that can only express 256 colors. It is a common format for network communication images.

PSD is mainly used as an intermediate transition of image files to save the channels and layers of images for later modification. The format is so poor that only Photoshop can use it, and few other applications support it.

JPE is not only a file format, but also a compression method. This compression is lossy, loss of size is not equal, and some are small enough to be discerned by the human eye.

16. What is the number of printed image screens? What is the relationship between it and the resolution of the image, the resolution of the scan, and the output resolution of the imagesetter?

A: Since the printed matter is composed of dots, the number of printed image lines refers to the number of screen lines per inch in the horizontal or vertical direction of the printed matter, that is, the number of screen network lines. The number of screen lines is called because the earliest print outlets are wired. The unit of the number of hanging lines is Line/Inch, or LPI for short. For example, 150 Lpi means that there are 150 network cables per inch. To screen images, the larger the number of linked screens, the greater the number of screens, the denser the network points, and the richer the level of expression.

Because the computer image is a lattice, it is composed of pixels (the smallest unit of the image is called a pixel). The image resolution can be visually understood as the number of pixels in a line per unit length in the horizontal or vertical direction. The more pixels are used to describe this line, the higher the resolution will be. The unit of image resolution is generally Pixels Per Inch, which is usually expressed in English as PPI. For example, an image with a resolution of 300 PPI means that it has 300 pixels per inch in the horizontal or vertical direction; an image with a resolution of 720 I means that it has 72 pixels per inch in the horizontal or vertical direction.

Some devices have similar resolution and image resolution, but they are represented by dots, so they are represented as Dot Per Inch, abbreviated as DPI. For example, an image scanner with a resolution of 1200 DPI has an image input accuracy of 1200 points per inch, or pixels. The 3600DPI laser imagesetter has an image output accuracy of 3600 laser spots per inch.

Image resolution PPI and print resolution LPI (screen plus line number) are related and different: the image resolution is higher than the print resolution, generally 2 × 2 pixels or more to generate a network, that is LPI is DPI About one-half.

17. What are the types of scanners?

Answer: 1 drum scanner: sub-grade drum scanner and small desktop drum scanner.

2 flatbed scanners: high, medium and low grades, as high and mid-range scanners should be used as a print design.

3 hand-held scanners for offices, etc.

4 film and transparent media scanners. Used for digitizing 35mm positive and negative films.

18. What are the commonly used output devices? What are the areas of application?

A: The designed page electronic file can be output by the following devices:

1. Black and white laser printer: used to print black and white proofs or final black and white official drafts.

2. Color laser printers: used to print color effect drafts or final color official drafts.

3. Color inkjet printer: used to print color effects.

4. Color large-format inkjet printer: used to print large-scale color effects or final color official drafts.

5. Digital proofer: used to check the content of the page, the effect of color.

6. Laser Phototypesetting Machine: Used to output the film used for printing.

7. Direct platemaker: Used to output printing plates.

8. Digital presses: Output directly from electronic pages. No film or plate is required.

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