Some technical points to be aware of when operating a flatbed scanner
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With the continuous improvement of the technical 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 functions 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.
1. 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 this state is selected, 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 scan
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 calibration in the C, M, Y, and K states of the printing dot; black and white in the brightness level appearing in the RGB format. Field, generally set white field between 170 ~ 255, black field between 0 ~ 85; appear in the form of original density, set the minimum and maximum density of the original white and black field calibration, some scanners釆Expressed in light and dark tones in numerical form.
In the above settings of highlight and dark tone, the printing dot is used in RGB format calibration. The color cast and contrast of the original can be adjusted greatly; when scanning at the maximum and minimum density, the contrast will be adjusted on the basis of ensuring the tone reproduction of the original.
(2) Setting of curve and gamma (Camma) values
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 density contrast of the transmissive manuscript, the reflection , and the printed matter are not the same, all the layers on the original are 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 individual curve states 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 85lpi (newspaper), 133 lpi (magazine), 150 lpi (general) and 175.Lpi (sample) four tops. 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 hue per unit area, so that a grid pattern is formed on the printed matter, which is commonly called "clay". 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, and the coarsest 85 of the dots Lpi has the largest adjustment range, and its image is also blurred accordingly.
Lpi has the smallest adjustment range. 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 the original More attention should be paid to the thicker photos and prints of silver salt particles. 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 300 dpi; output 175Lpi, the image resolution will of course increase accordingly. 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 improved to 1200 At dpi, the sawtooth 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. The operator needs to fully understand the main operating functions, adjustment range and performance capabilities. At the same time, he needs to have an understanding of the printing process and knowledge, and be familiar with the color forming laws of C, M, Y and K. This will better achieve a satisfactory image quality.