Scanning skills and correct storage of different types of originals

Selection of scanning methods for different manuscripts

Scanner scanning procedures generally provide us with three scanning methods: black and white, grayscale and color. Among them, the "black and white" method is suitable for originals with black characters on white paper, while the "grayscale" is suitable for mixed text and image files, and the color is suitable for scanning color photos. The scanning method also directly affects the scanning speed and the file size after scanning. Therefore, before scanning, we should first select a suitable scanning method according to the scanned object, so as to obtain a better scanning effect.

1. Line scan

For line drafts, select the scanning color mode "Line Art", only need to consider the dividing line that distinguishes black pixels and white pixels, you should pay attention to the setting of Threshold when scanning, that is, what tone content on the original is scanned into black, What content is white, so that it can retain enough detail in the brightest or darkest areas of the draft. Generally, the threshold value = 50% is taken as the standard value. If the test scan image is too dark, increase the threshold value, so that more gray edges can be converted into white pixels. If the test scan is too bright, reduce the threshold so that more gray edges can be converted to black pixels. Another issue to pay attention to is to determine the scanning resolution. The scanning resolution of the line draft should be higher than the scanning resolution of the continuously adjusted image. Generally, it should be above 600dpi to make the output line jagged very small, unclear to the naked eye, the image resolution is too low, will produce jagged.

2. Grayscale scanning

For some line text, you can also use 256-level grayscale scanning. The scanned image is relatively smooth compared to the Line Art mode, and the grayscale at some edges is better preserved. After scanning into Photoshop, you can adjust them as appropriate. Corrected to black. The original is in color, and to get a grayscale image and get a good level, it is best to use color scanning. Because the color image is highly saturated and rich in layers. If 256 Shades of Gray is used, some information may be lost. After scanning in RGB mode, and then converted to Gray in Photoshop, you can choose a certain channel information for conversion.

3. Scanning of color originals

The quality of color manuscripts is better. All parameters need to be set correctly when scanning color manuscripts. But for the defective manuscript, it should be corrected when scanning according to the actual situation. Some special manuscripts need special processing, such as color picture scanning on color newspapers. The color newsletter uses newsprint, so it has different characteristics from that of coated paper. The density value of the blank space of newsprint is about 0.15 to 0.2, which is equivalent to the sum of C: 3%, M: 4%, and Y: 10% of the dots on the coated paper, so the news paper is not white. Because newsprint has grayscale and loose paper, the ink spreads large, the ink absorption 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 (that is, the density is not enough). In short, the contrast of newsprint is small, only about 1.2, which determines that the four colors of C, M, Y, and K should be screened in a small area in the highlight, and the appropriate total amount of overprinting (not less than 250) should be applied in the dark colors. To increase the contrast. Color posters should not focus on gradation reproduction, more primary colors and intermediate colors should be used, basic colors should be reused instead of opposite colors or complementary colors, so that the colors are bright and bright. For the skin color part, the blue 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 relatively reduced.

4. Scanning of printed matter

Many prints have rose spots and moire. After scanning, the rose spots and moire are more obvious. Generally, the scanner has the function of removing the net. The essence of removing the net is to blur the image. The moire can be removed to obtain a smooth image. Therefore, when encountering printed manuscripts, generally choose the Descreen command. Going to the net when scanning is better than going to the net in Photoshop after scanning. The moire of some prints is very serious, and removing the screen during scanning will not make the image smooth. You need to continue to remove the screen in Photoshop; sometimes the image becomes too virtual after removing the screen. You can also use Unsharp mask in Photoshop to emphasize the clarity.

5. Scanning of transmission manuscripts

There are two types of transmissive manuscripts, positive and negative. Positive Transparency means positive and Negative Transparency means negative. Flatbed scanners generally use transparent glass to hold the negative film, and the light source illuminates the original from above the transparent glass. Usually the glass can be scanned directly without adding oil. The roller scanner is a method of covering the oil on both sides of the original with a transparent film, and the original frame is squeezed and evacuated. The scanning effect of negative film and positive film is different. At present, the scanning effect of the scanner on the positive film is better than that of the negative film, so it is best to choose the ideal positive film when selecting the original. It has better definition, rich layers and bright colors than the reflective film. Fine particles, suitable for large magnification scanning.

When scanning transmissive originals, cleaning the scanning roller and platform can reduce the generation of Newton rings. But if it still exists, you can use a duster equipped with corn flour, away from the scanner, squeeze the corn flour out of the duster and let it spread out in the air. Let it pass through the powder spraying area, so that the fine powder particles in the air fall on it, which can achieve the purpose of eliminating Newton's ring.

6. Barcode scanning

Like small text, the resolution of barcode scanning is higher than the resolution of general printed images, and it must be greater than 600dpi. In addition, it is better to set the scanning color mode to Gray mode. If you use a line draft binary image, it may cause edge aliasing.

The correct choice of storage method The storage format of image files can be generally divided into two categories: one is bitmap image files: the other is called vector graphics files, also known as drawing or object-oriented graphics image files. Bitmap image files describe graphic images in the form of a dot matrix, which is very suitable for expressing colorful works such as photos and oil paintings. The most representative processing software is currently very popular Photoshop. A vector file is a graphical image composed of geometric elements described by mathematical methods. Vector graphics do not need to record the information data of each pixel in the image like a bitmap, so it generally takes up much less disk space than bitmaps. In addition, because the expression of the image is detailed and true, and the resolution of the graphic image does not change after scaling, it has been widely used in professional-level graphic image processing. Specifically, in the image storage process, the most commonly used data formats are TIFF, EPS, and JPEG. The EPS and TIFF formats are the two most basic formats that desktop publishers are most interested in. The JPEG format affects those People who work on the Internet or multimedia most of the time like to use it. In addition, it also includes formats such as PDD, PNG, SVG, etc., but they are not commonly used, and they are usually converted into the above three formats when used. [next]

TIFF file format

TIFF is an abbreviation of Tagged Image File Format, which is a storage format defined for storing black and white images, grayscale images, and color images. It has now become an important file format in publishing multimedia CD-ROMs . The TIFF bitmap can have any size and resolution, and in theory it can have an infinite bit depth. TIFF format can encode grayscale, CMYK mode, indexed color mode or RGB mode. It can be saved in compressed and uncompressed formats. Almost all applications that involve bitmaps in their work can handle the TIFF file format—whether it is placing, printing, trimming, or editing bitmaps.

In TIFF files, no tool contains 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. However, the TIFF format can handle the clipping path, whether it is QuarkXPress or PageMaker, can read the clipping path, and can correctly reduce the background.

EPS file format

EPS is Encapsulated PostScript (Encapsulated PostScript) format, which is a page description language designed by Adobe to print files to any printer that supports PostScript language. The EPS file format can be used to encode pixel images, text, and vector graphics. If EPS is only used for pixel images, the information on the screen and the tone transfer curve can be retained in the file, while TIFF does not allow such information to be included in the image file. Because the EPS file is actually a collection of PostScript language codes, it can be printed in a variety of ways on a PostScript printer. The 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 and processed by the printer. There are hundreds of printers that support the PostScript language, including all image typesetting 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 compressed image file format. For occasions 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 will be a choice of compression ratio (image quality level) when saving, if you need high image quality, please choose high quality (High8 or higher) image compression method, the image capacity will be relatively Large; otherwise the file capacity becomes smaller, but the image quality will also be greatly reduced. There are 3 options in Format Option: Standard, Optimized and Progressive. The progressive method is for web page display, we can set the level of progressive display. The main disadvantage of the JPEG format is its biggest advantage. In other words, the lossy compression algorithm restricts JPEG to the display format, and some data is lost each time the JPEG format image is saved. Therefore, it is usually only necessary to save the image once in the JPEG format at the final stage of creation.

PDF file format

PDF is the abbreviation of Portable Document Format, which is an electronic document format, and is widely used in the transmission and preservation of Internet electronic files. The PDF format has built-in compression (JPEG, TIFF, LZW, and CCITT fax formats), and is generally composed of 4 parts, that is, a file header, file body, cross body (cross-reference table) composed of a line of characters, and a file end. At present, PDF files can be generated in various ways, such as Adobe's PDF Writer or Acrobat software package. Using Adobe Distiller, combined with the portable printer description file of the same name, you can convert the PS file into a PDF file and print it directly. All data in PDF files, such as color images, continuous tone images, monochrome images, and text and vector graphics, can be compressed using different compression methods, which also means that PDF files are usually better than original layout files and image files. smaller.

in conclusion

There are many other techniques for using the scanner. Here are just a few explanations about the precautions for scanning different kinds of originals. In the same way, the process of saving images is also very important. The correct saving format can be selected according to the purpose of the image, so as to reflect the efficiency and quality of the scanner. Only by truly mastering these skills can we scan real and ideal images.

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