In prepress image processing, the originals that we can currently reach are mostly originals based on traditional media, such as reversal films, photos, and printed manuscripts. For many reasons, there are also a large number of manuscripts used by the prepress production department in China, which are mostly printed manuscripts. We also call them manuscripts. When using this type of manuscript as an image acquisition source, the first problem to be solved is to remove the moiré.
As we all know, the reproduction of color images of printed materials is to rely on dot-nets to reproduce. There are four major characteristics in the printing of Internet sites. Among them, the number of dot lines added is one of them. It refers to the number of dots per inch. If you look through a magnifying glass, you will find that the dots are regularly arranged on the print.
Using Photoshop software, in the scanning of the second manuscript, there is an option to remove the moire in most of the scanning software. We only need to make a corresponding selection of the scanned manuscript. This article uses ScanWizan to scan the document. For example, to illustrate how to remove the texture in the second manuscript.
In the ScanWizan scanning software, open the scanning software, the dialog box of the scanning operation interface appears, as shown in Figure 1. In Figure 1, there is a de-networking option. All de-networking options are in the pull-down menu of the function. Click on the pull-down menu. There are several options in the popup box: "None, Newspaper, Magazine , exquisite magazines, custom." Among them, “None†means not to be reticulated. Which of the remaining four options will be selected depends on the dot size of the original image. If the scanned original image is a newspaper, that is, the image on the news paper. Then, the “newspaper†mode is selected. If the original image is a finer dot, that is, the image on the offset paper, when it is removed, the “heteroguide†mode is selected, if the scanned image is close to the quality of the photo, such as the image on the coated paper , then choose "exquisite magazine" mode when going to the reticulate, this processing is because newsprint, offset paper, coated paper three kinds of paper have different surface smoothness and whiteness, so the three in the printing process plus The number of screen lines is also different. After being arranged in the above order, the number of screens for the three lines is also increasing.
If after the removal process is performed by the above method, there is a certain moiré on the display of the scanned image, this indicates that the method of descreening is not thorough, and other types can be used, such as selecting the “custom†mode, and clicking This mode will pop up the dialog box shown in Figure 2, then we only need to enter the relevant value in the dialog box, the output parameter in the dialog box is the line value of the second original in the screen. As for what this value is, it requires you to know something about printing.
In the printing process, the most commonly used papers are newsprint, offset, and coated paper. Since the three types of paper each have their own printability, the number of screens used for printing using these three types of paper is also different. Under the paper, the smoother the paper, the higher the number of lines added to the screen. The higher the number of lines added, the stronger the detail of the image and the more exquisite the printed matter. In the specific printing process, the number of three kinds of paper screens is usually as follows: Newsprint is 80-85 lpi, offset paper is 100-133 lpi, and coated paper is between 150-200 lpi. From the actual production point of view, the hydrogen newsprint paper is set to 85 lpi, the offset paper is set to 120 lpi or 133 lpi or 100 lpi, and the coated paper is set to 150 lpi or 175 lpi.
After understanding this knowledge, you can analyze the secondary manuscript that needs to be scanned to estimate the number of screen lines for the first time the manuscript is printed. For example, if the secondary manuscript is a coated paper, the number of screens is 175 lpi. At this point, you can enter 175 lpi in the dialog box. After the above method is used, the print on the print can be generally removed, but after this treatment, sometimes the image will appear moire, then you have to make full use of Photoshop software in the relevant filter processing.
One way is to use Photoshop's "Filter / Blur / Gaussian Blur" option, then a dialog box will pop up, as shown in Figure 3. Enter the value in the value box. The experience value is “1â€. This principle is to blur the image to achieve the purpose of descreening, which can further weaken the texture. But pay attention to the value of fuzzy parameters, and then the image will become very virtual.
Another method is to use a single channel to remove moiré. The Y channel in the four channels of CMYK is the heaviest channel in the moire, so sometimes we can perform separate processing in the yellow channel to achieve further moire. As shown in Figure 5. Because any manipulation of the moire will make the picture virtual, in order to avoid this problem, to do the blur processing alone in the yellow channel, the clarity of the CMK three channels will not be affected.
Another method is threading, which involves scanning with a large number of lines while scanning, and then drawing lines in the "Image Size" option in Photoshop. For example, if a picture was originally scanned with 300dpi, it would be sufficient to scan it with 600dpi. After scanning, enter the "Image Size" option and change the resolution to 450dpi without changing the picture height. This means the picture is Withdrawing 150 lines and then drawing 150 lines, the resolution of the picture is returned to 300 dpi, as shown in Figure 6. In the process of drawing two lines, it is possible to remove the moiré.
In addition, using Photoshop in the "filter / noise / despeckle" can also achieve the purpose of the moiré, but the degree is weak, generally only applies to grayscale, there is a focus is to adjust the virtual, but generally only the drum scan The instrument has a focus adjustment function, so it does not apply to flatbed scanners.