Pre-print scan eight tips

1. The best scanning area for the platform scanner

Place the image in the best scanning area of ​​the scanner for the best, most faithful image.

Method: Set all scanner controls to automatic or default, select all areas, scan a blank, white, or opaque block sample at low resolution. Open Photoshop, and use the Image → Adjust → Homo mean command (Equalize menu item) to process it to see where there are cracks, streaks, or dark spots on the scanner. Print this file and cut out the best area (ie, the most stable area) to place the image.

2. Scan of line drawings

For the line draft, choose to scan the color mode "Line Art", only need to consider the distinction between the black pixels and white pixels of the dividing line, scanning should pay attention to the threshold (Threshold) setting, that is, what color tones on the original document is swept into black, Sweep what is white so that it retains enough detail in the brightest or darkest areas of the artwork. Normally, the threshold value = 50% is used as the standard value. If the test scan pattern is too dark, the threshold value is increased so that more gray edges can be converted to 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 linework should be higher than the scanning resolution of continuous tone images. Should be generally more than 600dpi to make the output line sawtooth is very small, the naked eye can not see clearly, the image resolution is too low, will produce jagged.

3 grayscale scan

Scans gray originals and selects 256 Shades of Gray for scanning color mode.

The main problem of scanning a gray manuscript is to pay attention to the level of the image, neither loss nor compression, so pay attention to the middle tone, high tone and dark tone. The high-profile of the image should pay special attention, because it has only one channel, unlike a color image, if there is a loss of one channel, there is still a certain level.

For some line text, you can also use 256 grayscale scans, the scanned image is smoother than the Line Art mode, and it is better to save the grayscale on some edges. After scanning in Photoshop, you can adjust them according to the situation. School to black.

The original is color, and to obtain a grayscale image, to obtain a good level, it is best to use color scanning. Because the color map is highly saturated, the layers are rich. If you use 256 Shadesof Gray, you may lose some information. After scanning in RGB mode and then in Grays in Photoshop, you can use the information of one channel to convert.

4. Scanning of color originals

The color originals are of good quality, and it is only necessary to set correct parameters for scanning color originals. However, for a defective manuscript, the actual situation should be corrected during scanning. Special processing is required for some special originals, such as color pictures on color newspapers. The newsletter uses newsprint, so it has different characteristics than offset printing. The density of newsprint blanks is about 0.15-0.2, which is equivalent to the sum of C: 3%, M: 4%, and Y: 10% of dots on coated paper, so newsprint is not white. Because newsprint is grayscale and paper is loose, ink is diffused, ink absorption is strong, and the reflectance of ink is low, even at a depth of 100% K, it is still not black (ie, the density is not enough). In short, the contrast of newsprint is only 1.2 or so, which determines that high-light areas should have small areas of C, M, Y, and K colors, and that the appropriate total overprint should be applied at the dark areas (not less than 250). To increase the contrast. In color newspapers, the level should not be reproduced as a key point. Primary colors and inter-colors should be used more frequently, and basic colors should be reused instead of using opposite colors or complementary colors to make the colors bright and lively. For the skin color part, the cyan plate should be used less in order to avoid graying and darkening, and the total amount of the three-color inks of C, M, and Y should also be reduced consciously.

5. Scanning of transmitted documents

There are two kinds of transparencies: positive and negative. Positive Transparency is positive, and Negative Transparency is negative. Flatbed scanners generally use transparent glass to hold the film in place. The light source illuminates the original from above the transparent glass. Normally, the glass can be scanned directly without refueling. The roller scanner is a method of wrapping oil on both sides of a document with a transparent film, and a document holder is used for squeezing out. The effect of negative and positive scanning is different. At present, the scanning effect of the scanner on the positive film is better than that of the negative film. Therefore, when selecting the original document, it is better to select the ideal positive film. It is better than the resolution of the reflection draft, rich in layers, and colorful. Fine particles, suitable for large magnification scans.

When scanning a transmissive original, cleaning the scanning roller and the stage can reduce the generation of Newton rings. But if it still exists, use a duster equipped with corn flour, away from the scanner, and squeeze the corn flour out of the duster so that it spreads out in the air. When the large particles fall, hold the translucent film. The corner of it, let it through the dusting area, so that the fine particles of the air fall on it, you can achieve the purpose of eliminating the Newton ring.

6. Scanning of prints

Many prints have rose spots and mottles, and after scanning, rose spots and moiré are more pronounced. In general, scanners have a de-networking function. The purpose of de-screening is to blur the image. You can remove the moiré and get a smooth image. Therefore, when encountering a printed document, the Descreen command is generally selected. Scanning to the Internet is better than scanning in Photoshop.

It should be noted that since the print density range is small and needs to be blurred, it is very suitable for flatbed scanners. In addition, some prints have very serious moiré patterns. Scanning to the net still does not make the image smooth. You need to continue to go to the Internet in Photoshop. Sometimes the image becomes too virtual after you go to the Internet. You can also use the Unsharp mask to emphasize the sharpness in Photoshop. .

7. Barcode scanning

Like fine text, the bar code scanning resolution is higher than that of normal printed images, and must be guaranteed to be greater than 600 dpi. In addition, it is better to set the scanning color mode to Gray mode. If you use a line art binary image, it may cause edge jaggies.

8. Get a rotating effect

Performing the rotation process while scanning requires a lot of memory and takes more time, and depending on the size of the rotation angle, the image quality (sharpness) is reduced. If you know in advance how the image is placed on the page, using the protractor and the bottom edge of the original to place the original at a precise angle on the platen and platform will result in the highest quality image without having to rotate it in the image processing software.


Li Yuanyuan Tang Qinghui Yan Yong Source: Digital Printing January 2003 No. 1