Fourth, the determination of markings
From an image analysis chart, in the phenomenon of marking we think, at least by two independent factors, the process acts like a non-linear way at the same time, and finally gives us the feeling of marking. Based on our definition of speckles, assuming that we divide the printed image into dark regions (lower than the average reflectance) and bright regions (above the average of the reflectivity), the speckle is the amount of change between the two groups of images. For the sake of clarity, we identify those spots in the image that are brighter or darker than the average background area as "spots." Sometimes these areas are also known as smearing, agglomeration, low quantification areas (fibers, flocs).
However, these spots can be described in two ways: size and reflectivity. We can feel the differences between bright spots and dark spots and their surrounding areas from the image. The size and contrast of these spots are referred to as the “particle morphology” of the markings.
We noticed that when the brightness decreased, we also reduced the feeling of markings or the severity of the markings. If we extend this trend further, we assume that the contrast of bright spots and dark spots is reduced sufficiently low, or the size of the spots is reduced sufficiently, we do not feel the appearance of markings. Also assume that the area of the spot is large enough to wrap around the entire printed area so that our eyes do not feel that they are segmented, and we will not call it a zebra. The actual situation is that - all printing areas have produced a certain level of markings, but due to the small area of the pattern or the low contrast, we do not feel the appearance of markings. So when the contrast is lower, the size of the bright areas and spots is not important. In other words, when the area of the spots is small, the eyes feel that the spots are integrated with the printed content of the whole block. For example, a halftone pattern is considered a brighter color. Therefore, the size and contrast of the spot are the direct factors that affect human vision.
Fifth, the test method to determine the markings
IGT, a Dutch company, used the printability instrument it produced to develop methods to determine the markings. Stripping and Wet-stretching The wet-resistance marking test was performed on an AIG2-5 printability tester. The peel-off speckle test was also performed on a CI-type printability tester. Wet pull resistance temperature test has been discussed in another article.
principle
The paper to be measured is printed with a special spectrophotometer. With the first method of measurement, the ink on the printed test strip is transferred to a clean printing plate. The test was transferred four times, each time using a clean printing plate.
Due to the irregularity of the ink absorbed by the paper, ink that has not been fully absorbed is transferred to the printing plate. With this method, the effect of markings has been strengthened, making assessment of results easier.
The second method is to print an inked printing plate onto five clean papers respectively, during which the printing plate does not need to be inked again. This method is faster but the test accuracy is poor.
the first method
The 50 mm blanket printing disc was inked with a speckle marking ink using conventional methods. The test strip was printed on AIC2-5. No padding is used for printing. The speed is 0.2m/s and the pressure is 500N. After printing for 10 seconds, the plate was printed again with 500N using another clean 50mm blanket printing plate. The ink on the paper is transferred to the printing plate. Every 10 seconds, print on the next clean print plate. A total of four stripping.
The test can also be carried out on C1 with a printing plate width of 35 mm and a pressure of 450 N. Volume is not all types of paper and paperboard suitable for testing on C1, the results can not be compared with the results obtained on AIC2-5. Please note.
The amount of ink used is based on the type of paper and board, but it is generally recommended to use 1cm3 for AIC2-5 and 0.3cm3 for C1.
The second method
The 50 mm print tray was inked and then printed on the AIC 2-5 at 0.2 m/s, 625 N. After 10 seconds, change a piece of paper and print it again. Use a clean strip of paper and print it 5 times, 10 seconds apart. If the type C1 is used, the pressure is set to 450N, and a printing cloth like a leather cloth is used. The ink is 0.3 cm3 on AIC2-5 and 0.5 cm3 on C1.
Test result evaluation
The method of assessment generally uses prefabricated, splined strips that represent a certain print quality.
This assessment method can only be used by the user. Unless comparison proofs can unify or use a speckle index table, they cannot exchange data with other units.
The zebra index is based on two conditions that influence the evaluation of zebra patterns: the perimeter of bright and dark spots and their density contrast. Larger areas and contrasts are easier to observe. With a scanner, the effective perimeter of bright and dark spots can be measured and expressed, and density changes can be calculated as Coefficient, Of Variables.
With the above two variables, the speckle index is obtained:
In the high-variable coefficient (large contrast) and small effective circumference (large spots), the speckle index increased, which is consistent with the results of visual assessment.
The relationship between printing quality and parameters related to the marking index can be expressed by the following table:
MI=COV/(SP)1/2
COV
SP
MI
Good print quality with less speckles
General printing quality spots large contrast low and some stripes small
General print quality, small spots, high contrast, some stripes, large middle
Poor print quality, large spots, high contrast, large, heavily striped, large
Speckle analysis is not a blind test on only a few samples. It is very important to clearly set goals and how to achieve them.
Source: BISENET
