Reflection Original Copy Point Analysis - Print Copy

Although there are only a few copies in the production of manuscripts for prints, various types of reprinted manuscripts have gradually begun to increase with the development of China’s opening up and cultural undertakings. Therefore, it is necessary to be familiar with its plate making method.

Printed manuscripts, because the printed material itself has a dot structure, and then copied when the screen is added, the two patterns will produce a beautiful pattern, or even a moire. This situation is particularly serious when originals are made large or when color separations are used to make plates. Only when the reduction magnification is more than one time, the reticulation on the printed matter will not play a role. Therefore, some measures need to be taken in the platemaking process to eliminate the effect of moire.

(a) Electronic scanning

1 small aperture completely open to a high degree of ambiguity;

2 four small holes with frosted film block, blur greater than 1;

3 four holes closed, the ambiguity is less than 1.

The electric division platelet to prevent the scanning film from reproducing the original printed network dots and generate the moiré, the lens focusing intentionally evaporates to the limit of not seeing the boundary lines of the manuscript network, and the slight level of emphasis is slightly increased than the normal manuscript. Other adjustments are the same as those for normal manuscripts.

(b) Desktop System

When scanning prints, we should pay attention to several issues. We will discuss them sequentially in the order of the lightest damage to the most serious damage to the image.

1. Remove moire by rotating

First, a series of methods similar to the adjustment of the screening angle can be used to eliminate the moiré fringes. Scanning an original at an angle and placing it correctly in Photoshop can sometimes avoid the appearance of a striped pattern. This is basically due to the average effect caused by Photoshop rotating pixels. If you work with a flatbed scanner, place the artist's triangle in the image along the edge of the platform and place it in the opposite direction so that you can know exactly where the image is. There will be a series of different angles to choose from. If one is not appropriate, try another.

When you need to scan the resulting image, select Image/Rotate/Arbitrary and enter the rotation angle as required. If you do not know the image rotation angle, you can also choose to freely rotate the selected area or cut the mask. When rotating the mask, press Optiop (Mac) or Alt (pc) to drag the mask to a vertex and you can rotate the image freely.

The next core technology to eliminate moire is the amount of softening of the image. Most of the image softening, how to do it accurately is actually a problem of how the image changes and makes itself feel more reasonable. The key is how much softening can remove the moiré fringe without substantially damaging the image quality.

2. Eliminating moire by lifting

When scanning an image with a flatbed scanner, the distance between the image and the glass platform can be made slightly out of focus by slightly raising the distance. Normally the depth of field of the mid-range scanner is limited, about 1/4 in. The easiest way to lift the image away from the countertop is to make a frame. We use some thin cardboard boxes with wrinkles to cut into many different lengths of paper to make a frame. The pieces can be glued together to make different sizes. The square shape, while the square size depends on the set of frames selected, this method not only has the flexibility to accommodate different sizes of originals but does not bend the original image. We have also seen people use a penny or dime coin to support the image away from the glass countertop. When this off-focus scan is done to get the image, it can be sharpened with a soft mask.

3. Eliminating moire by softening

Although the softening method will cause some loss of the image, it is still the most reliable method to eliminate Raul stripes and has the greatest flexibility. Flexibility here refers to the possibility of user input. Its basic steps are as follows:

1 Scan the image twice as much as the desired resolution, which is usually 4 times the number of screens;

2 soften the image;

3 half the resolution;

4 can be softened again when needed, using other filters to polish;

5 Sharpen to get a vivid and pleasing image.

Here are some details of these steps. The first thing to do is double the resolution needed. This has two purposes. First, it adds more image information and reduces the damage caused by various filters. Second, Moire fringes based on these pixels are more difficult to see when half of the pixels are removed.

Although scanning at such a high resolution is time-consuming and very slow, it must be done. Despite this, a low quality factor of 1.5 is acceptable for many output devices, which means that if output on a 150 line/in device, a pixel resolution of 225 can achieve acceptable results in scanning. The addition of letters in the image to 450dpi and 300dpi is comparable to the doubling of 600dpi in a 4x5in CMYK scan image, which is the difference between 27.5MB and 15.5MB.

We use two filters to eliminate moire. Despeckle (Filte/Noise/Despceckle) and Gaussian Blur (Filter/Blur/Gaussian Blur). There are two reasons why we use Gaussian softening instead of other softening filters. First, Gaussian softening followed by an omission in the filter window means that there are more freely chosen parameters.

Another reason to use Gaussian softening is to achieve better softening. Gaussian distribution can also be seen elsewhere in Photoshop, placing filter effects along the bell curve. The bell curve is a weak curve in the middle, which will reduce the effect of the filter, but it will not completely eliminate the effect of the filter. Other Blur filters can not do this, resulting in less than ideal results.

Gaussian softening works in 1/10th of a pixel, and the softening strength chosen is determined by the strength of the moiré fringe. The key is to choose a softened image so that it is sufficient to remove moiré without causing loss of detail. In our experience we have never used a softening value exceeding 1.8 pixels, and it is usually better to approach 0.7.

Before softening the image, all channels should be quickly checked to find out where the moire is. In general, moiré fringes only affect one or two channels, and the channels where these fringes are located are easily detected. If only the channel that softens the fringes exists, the image quality will not decrease too much.

Further testing of the moiré fringes is also possible. Once the fringes are found in the channel, the fringes and surrounding areas are selected. It should be clear that these fringes occupy the spatial gradation range. Therefore, the next step is to select the determined gradation range. By selecting the color range command, the color is selected, the stripe is selected, and the softening value is increased until the pixel value of the moiré region selected in the channel is equal to the neighboring pixel value. Select Gaussian Soften or select Dust and Scratches filters, then go back and check the work. If you choose to hide edge commands, you don't need to use a mask to get a selection area. This is also a good way to store selections. Repeat these steps for other channels where moire is present. It needs to be remembered that many other steps are needed to eliminate Raul stripes. In order to obtain a high-quality image, it is worth the trouble.

Next, reduce the resolution by half. In order to do this, select Image/File Size. Make sure that the options to limit the size change are not selected. Limit the file size change This feature uses the same number of pixel grids to limit the file size by simply adjusting the size of the pixels. Unchecking this option will cause Photoshop to add pixels, but what you normally need is to reduce pixels. Let's say that when removing half the pixels, the image quality should improve. If moire is still present, choose another smaller amount of softness to eliminate. It is also possible to find a ring-shaped rose spot consisting of dots, which does not necessarily have a bad influence if it does not cause a visual sensation. You can use the Despeckle filter (Filter/Noise/Despeckle) to eliminate rose spots. The filter searches for edges in the image and then gives slight softening to all pixels outside the edges of Chen.

Source: Shandong Printing Network