Some technical points to be noticed by the plane scanner
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With the continuous improvement of the performance of flatbed scanners and their price advantages, the number of users using flatbed scanners in color desktop systems is increasing. In order to meet the needs of the majority of users, in recent years, flat scanners are divided into professional and common types according to different grades, specifications and uses. Understanding the features of the flatbed scanner allows the operator to smoothly scan for better quality images. The following is a brief overview of the main functions and operating points of the flatbed scanner.
First, the choice of scanning method
The scanning method of the flatbed scanner can be divided into automatic and manual. These two different scanning methods will have different effects on image quality.
Automatic scanning
Automatic scanning refers to the "AI" function, also known as the "fool" function. When the automatic mode is selected for scanning, the scanner will scan the image for the first time to identify the pixel distribution and the highest density and the lowest density, so that the signals output by R, G, and B are adjusted after being processed by the computer, and then performed. Formal scan. For this reason, when scanning in the selected state, it should be noted that when setting the scanning range, do not select content other than the screen to be within the scanning format. If a white border, a black border, or a cover other than the screen is also selected within the set scan range, the information content that does not belong to the original is included in the screen. The automatic scanning software will make an incorrect judgment on the original information, and the main feature of the automatic scanning software for scanning images is to automatically find the black and white fields and calculate the contrast under the premise that the neutral gray balance setting is correct, so that the image is scanned. Can achieve replication and restore. Therefore, when using the automatic scanning function, it is necessary to notice whether the original has a color cast, whether the contrast is appropriate, and the like. Otherwise, the image quality will not be as good as when scanning images with the automatic function.
2. Manual scanning
In most cases, we need to use a scan in the manual state. This method can effectively adjust the color cast, contrast and curve state of the original to better represent the level of a certain part of the original. When performing a manual status scan, a series of dialog boxes will appear, which need to be set for each scan. Common scanners generally have the following settings.
(1) Settings for highlights and shadows
The setting of highlight and dark tone is also called the setting of white field and black field. According to the scanning software set by the scanner, it can be roughly divided into the following three cases: black and white field in the C, M, Y and K states of the printing network. Calibration; black and white fields are set in the brightness level appearing in RGB form. Generally, the white field is between 170 and 255, and the black field is between 0 and 85; in the form of original density, the minimum and maximum density of the original are set. The white field and the black field are scaled, and some scanners are represented by a digital level in the form of light and dark.
In the above settings of highlight and dark tone, the printing dot RGB format is used for calibration. The color cast and contrast of the original can be adjusted to a large extent; when scanning at the maximum and minimum density, the contrast is adjusted on the basis of ensuring the tone reproduction of the original.
(2) Curve (Curve) and gamma (Camma) value settings
The state of the curve and the setting of the gamma curve will relate to the hierarchical representation of the image after scanning. Since the contrast of the density of the transmission, reflection, and print is different, all the layers on the original should be copied on the printed matter, so that the bright, middle, and dark adjustments are fully expressed on the paper, and it is necessary to respond to many different reproductions. Adjust the state of the curve. Since most of the software of the flatbed scanner can not only adjust the whole curve, but also adjust the state of individual curves in the form of scales R, G, and B, respectively. In this way, we can trim the neutral gray balance of the ink and also handle the overall color cast of the original.
Second, the scanning settings of printed originals
In the top setting, it is generally divided into eight tops of 85 lpi (newspaper), 133 lpi (magazine), 150 lpi (general), and 175 lpi (sample). Since the printed product is composed of dots, the copying is performed on the basis of the existing dots of the original dot, and an interference pattern is generated at this time. When an image having an interference pattern is printed, an irregular pattern is formed on the color tone per unit area, so that a grid pattern is formed on the printed matter, which is commonly called "clay pattern". This setting of the flatbed scanner. Actually, the scanning focal length is adjusted so that the scanner cannot distinguish the dots of the printed products. Therefore, when this setting is made, the image sharpness is affected to a certain extent, wherein the 85 lpi of the coarsest dot is the largest, and the image is correspondingly blurred, and the finest 175 lpi of the dot is the smallest. Therefore, when the printed network of the printed original cannot be determined, in order to maintain the sharpness of the image as much as possible, the scanning should be started from the selection of the thinner network setting until no "clay" appears.
Third, the setting of sharpness
It should be pointed out here that the sharpness is not equal to the sharpness. Although the sharpness is improved, the clarity is improved in visual effect. On the other hand, excessively sharpening the sharpness will make the image rough, especially when the original photo and printed matter with coarse silver salt particles are used. In a flatbed scanner. The sharpness of the image is determined by the optical resolution of the scanner; sharpness produces a white and black border in the area between high and low density. Make it visually enhance clarity. For such a computer-generated line, it will be determined by three factors: depth (Amount), range (Radius), and threshold (Threshold). Some scanning software divides the sharpness into several levels, such as slight, medium, and emphasized. In general, the reversal film can choose a slightly higher sharpness, the photo can choose medium sharpness, and the print can choose a slight sharpness. In addition, for the original expression content, such as still life, the sharpness of the landscape can be slightly higher. For people, etc., you can choose a setting with a lower tax rate.
Fourth, the image resolution settings
The resolution of the image should be determined according to the network cable of the final output film. In general, the image resolution should be set to 2 times the output network cable. Such as: output 150lpi, image resolution should be 300dpi; output 175lpi, image resolution, of course, correspondingly improved. Set the resolution higher. The corresponding level of reflection may be better, but the amount of files will increase and the speed of scanning, transferring, and producing files will be greatly reduced. On the contrary, the image with too low resolution will greatly reduce the content contained. Although the file size is reduced, the file transfer speed and the production speed are improved, but the output film will not be able to match the output precision of the film in the image portion due to the image resolution. Mosaic phenomenon.
When performing line scans, set the image resolution as normal. There will be a lot of sawtooth on the line turns and slashes. It brings a lot of trouble to post-production. When the image resolution is increased to 1200 dpi, the aliasing phenomenon will be greatly reduced. Of course, when the image resolution is increased, the scanning speed is lowered due to an increase in the amount of the file. However, after scanning, the resolution of the file can be reduced to a normal state so as not to affect the transfer speed and production speed of the file.
The operation of each flatbed scanner is different, but their basic operations are generally the same. Operators need to have a full understanding of the main operating functions, adjustment range and performance capabilities, as well as a good understanding of the printing process and knowledge, familiar with the color of C, M, Y, K. This will better achieve a satisfactory image quality.