Despite the maturity of CTP technology, laser imagesetters still maintain their strong production. In the printed publications such as commodity packaging and books and magazines, there is still a considerable portion of the process of designing, producing, outputting, and finally printing finished products. The quality of the photo-discharge film is directly related to the quality of the final printed product. This shows that there are still many fields in the traditional process that need to be studied and explored. Here I will talk about the experience of prepress quality control from the perspective of process management.
From the perspective of total quality management, the quality of the control photographs must be started from the manuscript. Since the quality of the manuscript determines the quality of the photographs, the manuscript must be carefully examined.
1. Check whether the surface of the original is scratched or dirty, whether the characters and lines are complete or not, and whether there is any missing or broken picture.
2. Check if the screen is color cast. Under natural light or a standard light source close to sunlight, observe whether the white, gray, black, and other achromats on the reflective document have other colors.
3. Check if the main color is accurate. In general, the colors of reflective drafts (such as photos) are slightly exaggerated than the actual scene colors, such as more vivid than the original colors. The reflection draft based on characters should be based on the ruddy face color.
4. Check if the contrast is moderate. The contrast of the reflection draft includes luminance difference, color contrast and contrast balance. With a moderate brightness difference, there will be a rich transitional color hierarchy between the high-profile part and the darker part; the color contrast is moderate, the reflection text color density is large, and it has a strong stereoscopic effect; the contrast balance is good, and the same color is in the high-profile part The color reproduction will be consistent with the dark tone.
Output document quality
The main inspection items for the documents that need to be output as the following:
1. Check whether the setting lines, color marks, and various printing and cutting lines are fully set. Overprinting lines should be four-color black (C100, M100, Y100, K100). If there is no overprinting line, the output of four or more color photos is equivalent to a pile of waste.
2. Check the image color mode. When the laser imagesetter outputs the color separation film, all color images are in the CMYK color mode. Therefore, before the output, check whether the color mode of the linked image is correct through the linked image table. If the color image color mode is RGB or Lab mode, the mode conversion should be performed in the image processing software. Otherwise, only the black version will have an image when the output color separation is output, or the color separation situation is not ideal or even impossible; if it is black and white For images, the image mode should be grayscale or binary.
3. Check that the resolution of the images used meets the printing requirements. Ensure that the scanned images, photos, and other bitmap images have the appropriate resolution, which is necessary to ensure the quality of the output photos.
The resolution of print images is generally set to 1.5 to 2 times the number of dot lines. The resolution of some common publications is set as follows: the scanning resolution of newspapers is 125 to 170 dpi, and the number of dot lines for newspaper printing is 85 to 133 lines/inch; journals, magazines, and promotional materials have a scanning resolution of 300 dpi, because the number of dot lines for printing is 133 lines/inch or 150 lines/inch; the high-quality album uses a scanning resolution of 350 to 400 dpi. Most of the finely printed brochures use dot line counts of 175 to 200 lines per inch. It is best not to use images downloaded on the Internet, because the resolution of these images is generally only 72dpi, and some are even lower. No matter how they are processed, the output will not be good.
4. Interpret the preview hairline results by RIP. The RIP interpretation preview is consistent with the final hair print result. By previewing the control original or proof, check whether the linked image of the file is correct, whether the image interpretation is in good condition (if the image is copied incorrectly, RIP interpretation will be wrong), and whether the image color is Consistent with the manuscript, whether the text is garbled, whether the various elements of the document are misplaced, and whether the black version is overprinted. This is the last check before the output, so be careful to avoid quality problems.
After the imagesetter is started, its working status can generally be seen in the graphical interface of the control software of the output workstation. The items that need to be checked are:
1. The settings of the laser imagesetter and the system equipment match and operate normally. In order to ensure the stability of the laser energy, the laser head should be tested and corrected regularly.
2. The liquid concentration and temperature of the punching machine are normal. According to the photo film and the performance of liquid medicine set the value of development, fixing parameters, regular test with the test strip and a ruler, while doing a good job of the washing machine's daily cleaning and maintenance work to prevent sediment to make photo film with dirty.
3. The photo-discharge film and the liquid's own performance are stable. In order to ensure the stability of the quality of photostrips, the use of raw materials should minimize the variable factors, so that the use of raw materials is relatively fixed.
4. Photographic film is easily scratched by foreign materials during the operation and transmission of the equipment. The transmission parts should be cleaned and wiped regularly. Once the components are found to be damaged, they should be promptly replaced.
Output film quality
The inspection of the output film quality, as the last process of filming, should really play a role in remedying plugging and plugging, so we should pay enough attention to it.
1. Check the fitting accuracy. In general, the coupling error of continuous output four- or multi-color film is very small, if one job needs to fill in one color or two colors, and the other color film is one day, two days or longer Output, at this time should carefully check the color film of the matching accuracy, if the fitting error is large, you should continuously output all color version of the film. Of course, this should be based on the use of the image-setter, the stability of the work, and some imagesetters even if the four-color film continuous assembly error is very large, then you should consider the maintenance or update the machine.
2. Check the imprinting relationship of each color version against the original or proof. Occasionally, layout elements may be lost or misplaced due to personnel operations or machine failures. For books and magazines, the best way to check is to attach the film to the original or the proof. If there is any error, it will be clearly visible. Of course, in this process, care must be taken to avoid scratches on the film and affect the quality of the print.
3. Check if the film is dirty. Dirty film is a common problem in the output process. Generally speaking, the washing tank should be cleaned before starting the machine every day. Before the water injection, the water purification equipment of the external water supply switch should be turned on to prevent the sediment deposited in the pipeline from being carried into the washing tank, scratching or adhering to the film. Film quality. After the work is finished, empty the washing tank and carefully clean it.
4. Check the screen angle of the colored output film. In order to avoid hitting the net, in theory, there should be a difference of 22.5Â° between the four colors, and in actual production four-color printing uses 15Â°, 45Â°, 75Â° and 90Â° more. Among them, the yellow version has weak visual stimuli and poor visual perception, so it is generally set to 90Â°. Since human vision is most sensitive to 45Â°, the main color version of the original is generally set to 45Â°. The specific settings should be based on the design of the print product. The angle of the cable can be checked through the magnifying glass on the angle of the screen of each color version of the film, or can be measured using the cable angle measurement tool. In addition to customer special requirements, the general network cable angle setting should not be arbitrarily changed to avoid unnecessary losses.
5. Check the on-site density of the output film. Through the transmission densitometer to check the density of the film on the ground, it is generally required to be above 3.5, preferably around 4.2. If the density is too high, the phenomenon of stencil printing will occur. If the density is too low, the ink will be subdued and unrealistic for printed materials with text and on-site layout. At this time, it is necessary to consider replacing the fixing solution or cleaning the laser head to ensure the stability of the output film quality.
In summary, the pre-press output process is carefully and accurately checked, and corresponding measures are taken to control it. Not only can the quality of the photo-discharge film be improved, but also the production efficiency can be improved.
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