Printing FAQ (13-17)

13, what is the laser value? How to adjust?

A: The laser value refers to the amount of exposure of a row of lasers. It not only determines the density of the film on the ground and the value of the software display screen value and the output screen value of the imagesetter, but also closely relates to the life of the laser. Therefore, the control rower should select an appropriate laser value in the development and fixing conditions ( When the temperature and time are relatively fixed, the solid density D of the film is ≥ 4.0. When the percentage of dots with 50% is greater than 52%, the laser value can be appropriately reduced; when the percentage of dots with 50% is less than 48%, The laser value can be increased appropriately, and the amplitude of the laser value should be increased and decreased so that the percentage error of the halftone dot of 50% is within ±2%. Similarly, when D is less than 4.0, the laser value should be appropriately reduced when the halftone value at 50% is greater than 52%, and the laser value should be appropriately increased when the halftone value at 50% is less than 48%. . Different types of film laser exposure will be different, so each time you change the film type, the laser value should be re-tested, in the case of fixed, fixed and fixed film, the laser exposure is relatively fixed, there is not meet the requirements Places can be adjusted by linearizing the film.

14, what is the image resolution? Why emphasize it?

A: The resolution of printed images has been introduced in the basic part of printing. We know that high-resolution images contain more pixels than images of the same size and low-resolution, and there are more image information and more detailed representations. This is One of the reasons for determining image resolution considering output factors. Because of the different uses of the image, the resolution should be determined based on the use of the image. If an image is displayed on the screen, the resolution is 72Dpi or 96Dpi; if it is used for a 600Dpi printer output, it needs an image resolution of 150Dpi; to print, 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 occupied disk space is large, which does not conform to the principle of high efficiency; if the resolution is too low, the expression of the image details is affected and does not meet the principle of high quality. Greater China Graphic Arts Network

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

PerInch (pixels/inch), 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, referred to 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.

-----Great China Graphic Arts Network