Print knowledge summary 5B
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Printing dot basic knowledge
In the printing process, the continuous blending of halftone images is adjusted by the density of the dots. By mixing CMYK four-color dots, you can display an infinite number of colors.
There are two main types of outlets currently used in the printing process: amplitude modulation (AM) and frequency modulation (FM).
AM outlets
AM sites are currently the most widely used network. Its density of dots is fixed, and the shades of color are expressed by adjusting the size of the dots, thus achieving the transition of tone. In printing, the use of AM sites requires consideration of network size, dot shape, dot angle, and cable accuracy.
Dot size
The dot size is determined by the coverage of the dot, also known as the ink rate. Generally speaking, it is customary to use "succeeding" as a unit of measure. For example, a 10% coverage network is called a "10% outlet", an outlet with a 20% coverage is called a "20% outlet", and an outlet with a coverage of 0% is called For "absolute network", the coverage of 100% of the network is called "in the field."
The tone of printed matter is generally divided into three levels: bright tone, mid tone, and dark tone. The dot coverage of the highlighted part is about 10% to 30%; the coverage of the halftone part is about 40% to 60%; and the dark part is 70% to 90%. The net and field parts are additionally divided.
Dot shape
The dot shape in printing is not only a kind of circular shape that everyone imagines. It can be divided into three types: square, round, and rhombus with the shape shown by dots at the 50% inking rate.
Square dots are shaped like chessboards with 50% coverage. Its granules are relatively sharp, and its ability to express levels is strong. Suitable for lines, graphics and some hard-coded images.
In the case of a circular dot, either in the bright tone or in the middle tone, the dots are independent and only partially connected. Therefore, the performance level for the mining level is poor, and it is rarely used in four-color printing.
The diamond-shaped dots integrate the hard-tone of the square dots and the soft-adjustment of the circular dots. The color transition is natural, which is suitable for the performance of general images and photos.
Dot angle
In the printing plate making, the choice of dot angle has a crucial role. Choosing the wrong dot angle will cause interference fringes.
The common dot angles are 90 degrees, 15 degrees, 45 degrees, and 75 degrees. The 45-degree network has the best performance, is stable and does not appear dull; the 15 degree and 75 degree angle stability is worse, but the visual effect is not rigid; the 90 degree angle is the most stable, but the visual effect is too rigid There is no beauty.
If two or more types of dots are put together, there will be mutual interference. When the interference is serious enough to affect the appearance of the image, the so-called “rhizard pattern” appears.
In general, when the angle difference between the two types of dots is 30 degrees and 60 degrees, the overall interference fringe is still more beautiful; the dot angle difference of 45 degrees is next; when the angle difference between the two dots is 15 degrees and 75 degrees When the interference fringes can damage the image.
Dot number
The number of screen lines determines the fineness of the image, similar to the resolution. The common line number is applied as follows:
Line 10-120: Prints of low quality, long-distance prints such as posters and posters are generally printed using newsprint paper or offset paper, and sub-powder paper and coated paper are sometimes used.
150 lines: Normal four-color printing generally use this accuracy, all types of paper have.
Line 175-200: exquisite albums, pictorials, etc., mostly printed on coated paper
250-300 lines: The most demanding albums, etc., are mostly printed on premium coated paper and specialty paper.
The following are the effect of pictures under several different line conditions (the effect on the screen is really bad, only for reference)
Screening dot point
The screen adjustment network point is a newly developed screening method since the 1990s. Its difference from the amplitude modulation network point is that the size of the network screen point of the screen adjustment network is fixed, and it is achieved by controlling the denseness of network points. The dots in the highlights are sparse, and the dots in the shadow tone are dense.
How many dots are seen from the webscope.
One-tenth of network: Just three similarly-sized dots are placed between the two corners of the network.
Zengcheng.com: Just two similarly sized outlets between the two outlets in the diagonal.
Three-tenths of nets: Just two 1.5-square-dot nets were placed between two corners of the diagonal.
Four-tenths of nets: Just 1.25 equally-sized nets are placed between two corners of the diagonal network.
50% of the net: Just two nets of the same size are placed between the two opposite corners.
One-tenth network corresponds to Jiucheng. The second part of the network corresponds to Bacheng. The 30% network corresponds to Qicheng. 40% of the net corresponds to 60% of the net. Only the size of the outlets is just the opposite of the distance between them.
(A bitmap with a resolution of 300, we know that he is saying that each inch consists of 300 square pixels in each direction. After the image is enlarged, it will be found that it is composed of numerous meshes of various sizes. Since the printed matter is composed of dots, the number of printed image lines refers to the number of screen lines per inch in the horizontal or vertical direction of the printed matter, that is, the number of screen network lines. The number of screen lines is called because the earliest printed network sites are wired. The unit of line number is Line/Inch, or LPI for short, for example, 150 Lpi means that there are 150 network lines per inch.To screen images, the larger the number of screens, the more the number of screens, the more dense the screens are. The greater the level of expression, the larger the dot, the deeper the color of the expression, and the darker the layer, and the smaller the dots, the lighter the color of the expression, the brighter the represented layer, the line accuracy (Lpi) and the resolution (Dpi). ) Corresponding to 1:1, such as 150 lines of the picture requires about 300Dpi resolution. Resolution is about twice the number of lines. If you do not pay attention to theory, it can be understood as the density of film or ink!)
Inter-color: The mixed color prepared by mixing two primary colors is called inter-color or secondary color. For example, R, G, B, M80%, Y70%, C20%, and Y80% can be called inter-color. Color is also called secondary color
Duplex color: The color produced by mixing the primary color with the inter-color, or the color produced by mixing the two inter-colors is called a polychromatic or tertiary color. In fact, the polychromatic color is a mixture of three primary colors, but it is based on a combination of primary colors.
Complementary color: When the two color materials are mixed, they are black, and the two colors are complementary. The color between any one of the three primary colors and the other two primary colors is a complementary color. For example, M and G are complementary colors. The two shades of light, if mixed to form white, are complementary to each other.
What is the trapping value based on? Where is the difference between Choke and Spread? What does Keep away mean?
(1) Trap control is performed at the interface where two colors are transferred. The shrinkage or expansion of its foreground (or background), hollowing out, or emptying are all called trapping values. In order to avoid glazing at the overlap, the trapping value should be slightly larger than the four-color registration accuracy of the printing press. Due to the different printing processes used in various color prints, as well as the precision of paper and printing machinery, the more precise the printed matter, the higher the precision of registration and the lower the trapping value. The United States Printing Service and printing plants have published typical trapping values. For example: sheetfed offset printing, the use of copperplate paper dot line number is 150lpi, the trapping value is 0.08mm; newsprint web offset, the number of lines is 100lpi, the trapping value is 0.15mm.
(2) Shrinkage is the increase in the area of the (light-colored) background so that it will intrude into the darker foreground (text or figure) at the boundary, while maintaining the shape of the foreground contour unchanged.
The expansion is to increase the foreground area of the lighter color, so that it will invade the background area with a darker color on the boundary, while maintaining the shape of the background outline.
(3) Let empty when the background is black, and the foreground is hollowed out, the three shades of CMY need to be dealt with when empty, so that the foreground contour is defined by the monochrome black version.
