Scanning techniques and proper storage of different types of originals
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It is well known that a scanner is an input device that converts an analog manuscript into a digital image. Whether it is a resource for network transmission or a requirement for enriching the content of the print, the role played by the scanner is very important. Scanners currently on the market mainly include flatbed scanners, roller scanners, and hand-held scanners. Of course, they can be further subdivided. For the operation of the scanner, not only the equipment should be selected according to different types of originals, but also the scanning mode or storage mode should be correctly selected to improve the scanning quality.
Scanning method for different originals The scanner's scanning program generally provides us with three scanning methods: black and white, grayscale and color. The "black and white" method is suitable for originals with black and white text, while "grayscale" is suitable for graphic and text files, and color is suitable for scanning color photos. The scanning method also directly affects the scanning speed and the size of the scanned file. Therefore, before scanning, we should select a suitable scanning method according to the scanned object, so as to obtain a better scanning effect.
1. Scanning of line drawings
For line drafts, select the scan color mode "Line Art", just consider the distinction between black pixels and white pixels. You should pay attention to the Threshold setting when scanning, that is, what color of the original is scanned black, what is scanned white, so that it is The brightest or darkest areas of the draft can retain enough detail. Generally, the threshold = 50% is the standard value. If the test scan is too dark, increase the threshold, which will convert more gray edges into white pixels. If the test scans If the graph is too bright, the threshold is reduced, which converts more gray edges into black pixels. Another issue to be aware of is to determine the scanning resolution. The scanning resolution of the line draft should be higher than the scanning resolution of the continuous tone image. Generally, it should be above 600dpi to make the output lines have small serrations, which are not visible to the naked eye, and the image resolution is too low, resulting in jaggedness.
2. Grayscale scanning
For some line texts, you can also use 256-level grayscale scanning. The scanned image is relatively linear. The Art mode is smooth, and the grayscale at some edges is better preserved. After scanning into Photoshop, you can adjust them to black as appropriate. The original is colored, and to obtain a grayscale image, a good level is obtained, preferably by color scanning. Because the color map has high saturation and rich layers. If 256 Shades of Gray may lose some information. After scanning in RGB mode, it will be converted to Gray in Photoshop. When converting, you can use the information of a certain channel to convert.
3. Scanning of color originals
The quality of the color original is good. When scanning the color original, you only need to set the parameters correctly. However, for defective originals, it is necessary to correct them during scanning depending on the actual situation. Special handling of special manuscripts, such as color image scanning on color newspapers. The color newspaper uses newsprint, so it has different characteristics from coated paper. The density value of the newsprint blank is about 0.15~0.2, which is equivalent to the sum of C:3%, M:4%, and Y:10% on the coated paper. Therefore, the news paper is not white. Since the newsprint has gray scale and loose paper, the ink spreads greatly, the ink absorbability is strong, and the reflectivity of the ink is low, so even if 100% K is given at the deepest point, it is still not black enough (ie, the density is insufficient). In short, the contrast of newsprint is small, only about 1.2, which determines that the high-gloss area should have a small area of C, M, Y, K, and the appropriate amount of overprint (four no less than 250) in the dark tone. To increase the contrast. The color report should not focus on the reproduction of the layer. The primary color and the intermediate color should be used more, and the basic color should be reused instead of the opposite color or complementary color to make the color bright and vivid. For the skin color part, the green version should be used less to avoid graying and darkening, and the total amount of C, M, and Y ink overprinting should also be consciously reduced.
4. Print of printed matter
Many prints have rose spots and moiré, and after scanning, the rose spots and moiré are more pronounced. Generally, the scanner has a function of going to the network, and the essence of the network is to blur the image. You can remove the moiré and get a smooth image. Therefore, when encountering a printed original, it is generally necessary to select the Descreen command. Going to the web during scanning is better than going to the web in Photoshop after scanning.
Some of the prints have very serious moiré. You can't make the image smooth after scanning. You need to continue to go to the net in Photoshop. Sometimes the image becomes too virtual after going to the net. You can also use Unsharp in Photoshop.
Mask emphasizes clarity.
5. Transmitted scanning
The transmission has two kinds of positive and negative, Positive Transparency means positive film, Negative Transparency represents negatives. Flatbed scanners generally use a transparent glass to press the backsheet. The light source illuminates the original from above the transparent glass. Usually the glass can be scanned directly without adding oil. The roll scanner is a method of wrapping the oil on both sides of the original with a transparent film, and the original frame is squeezed and evacuated. Negative film and positive film scanning have different effects. At present, the scanning effect of the positive film is better than that of the negative film. Therefore, it is better to select the ideal positive film when selecting the original. It is better than the clarity of the reflective draft, rich in layers and colorful, and Fine particles, suitable for large magnification scanning.
When scanning a transmissive original, cleaning the scanning roller and the platform can reduce the generation of Newton's rings. But if it still exists, use a duster with corn flour, keep away from the scanner, squeeze the corn flour out of the duster, let it spread out in the air, and when the large particles fall, hold the transmission. In the corner, let it pass through the dusting area, so that fine particles in the air fall on it, which can eliminate the Newton's ring.
6. Barcode scanning
Like small text, the resolution of bar code scanning is higher than that of normal printed images, and it is guaranteed to be greater than 600dpi. In addition, it is better to set the scanning color mode to Gray mode. If the binary image of the line is used, it may cause edge aliasing.
The correct choice of storage mode Image file storage format can be divided into two categories: one is a bitmap image file: the other is called a vector file, also known as a drawing class or object-oriented graphic image file. Bitmap image files describe graphic images in a dot matrix format, making them ideal for color-rich works such as photographs and oil paintings. The most representative processing software is currently very popular Photoshop.
A vector file is a graphical image of geometric elements described mathematically. The vector does not need to record the information data of each pixel in the image like a bitmap, so its disk space is generally much smaller than the bitmap. In addition, since the expression of the image is detailed, real and the resolution of the scaled image does not change any more, it has been widely used in professional-level graphic image processing. Specifically, the most commonly used TIFF, EPS, and JPEG formats are the data formats. The EPS and TIFF formats are the two basic formats that desktop publishers are most interested in; The format affects those who prefer to work on the Internet or multimedia most of the time. In addition, formats such as PDD, PNG, and SVG are also included, but they are not commonly used, and are usually converted into the above three formats when used.
TIFF file format
TIFF is Tagged Image File The abbreviation of Format (marked image file format), which is a storage format defined for storing black and white images, grayscale images and color images, has now become a publishing multimedia. An important file format in the CD-ROM. A TIFF bitmap can have any size and resolution, and in theory it can have an infinite bit depth. The TIFF format encodes grayscale, CMYK mode, indexed color mode, or RGB mode. It can be saved in both compressed and uncompressed formats. Almost all applications that involve bitmaps in their work can handle TIFF file formats—whether they are placed, printed, trimmed, or edited. In the TIFF file, no tools contain screen processing instructions. Screen processing is controlled by a program that prints TIFF format files. If you want to save the screen processing instructions while saving the bitmap, you must use the EPS file format. But the TIFF format can handle the clipping path, and both QuarkXPress and PageMaker can read the clipping path and correctly subtract the background.
EPS file format
EPS is encapsulated PostScript (Encapsulated PostScript) format is Adobe The page description language that the company designs to print files to any printer that supports the PostScript language. The EPS file format can be used for encoding of pixel images, text, and vector graphics. If the EPS is only used for pixel images, the net information and the tone copy transfer curve can be retained in the file, while TIFF does not allow such information to be included in the image file. Since the EPS file is actually a collection of PostScript language code, it can be printed in a variety of ways on a PostScript printer. Software that creates or edits EPS files can define capacity, resolution, fonts, and other formatting and printing information. This information is embedded in the EPS file and then read in and processed by the printer. There are hundreds of printers that support the PostScript language, including all image layout systems used in the desktop publishing industry. Therefore, the EPS format is a file format used by the professional publishing and printing industries.
JPEG file format
JPEG is the most common type of compressed image file. For applications where image accuracy is not high and a large number of image files need to be stored (website), JPEG is the best choice. But remember that JPEG is a lossy compressed file format. There is a compression ratio (image quality level) when saving. If you want high image quality, please select high quality (High 8 or above) image compression mode, the image capacity will be relatively high. Large; on the contrary, the file size becomes smaller, but the image quality is greatly reduced. In Format There are three options in Option: Standard, Optimization, and Progressive. The progressive method is for web page display, we can set the level of progressive display. The main shortcoming of the JPEG format is its greatest advantage. That is to say, the lossy compression algorithm limits JPEG to the display format only, and some data is lost each time the JPEG format image is saved. Therefore, it is usually only necessary to save an image in JPEG format at the final stage of creation.
PDF file format
PDF is a Portable Document The abbreviation of Format, which belongs to the electronic document format, is widely used in the transmission and storage of Internet electronic files. The PDF format has built-in compression (JPEG, TIFF LZW and CCITT fax formats), which is generally composed of four parts, that is, a line header, a file body, a cross body (cross-reference table), and a file tail. PDF files can now be generated in a variety of ways, such as Adobe's PDF Writer or Acrobat package. Use Adobe Distiller, combined with a portable printer description file of the same name, to convert the PS file into PDF files are printed directly. All data in a PDF file, such as color images, continuous tone images, monochrome images, and text and vector graphics, can be compressed using different compression methods, which means that PDF files are usually smaller than the original layout files and image files. smaller.
in conclusion
There are many other tips for using the scanner. Here are just a few notes on the precautions for scanning different types of originals. In the same way, the process of saving images is also very important. According to the purpose of the image, the correct storage format can be selected to reflect the efficiency and quality of the scanner. Only by mastering these skills can you scan real and ideal images.