In the printing process, continuous tone and halftone images are adjusted by the density of the dots. By mixing CMYK four-color dots, you can express an infinite number of colors. There are two main types of dots currently used in the printing process: AM dots and FM dots.
Amplitude modulation outlets are currently the most widely used outlets. Its dot density is fixed, and by adjusting the size of the dots to express the depth of color, so as to achieve the transition of tones. In printing, the use of amplitude modulation dots mainly needs to consider factors such as dot size, dot shape, dot angle, and line accuracy.
The dot size is determined by the coverage rate of the dot, also known as the ink rate. It is customary to like to use "come" as the unit of measurement, for example, the outlets with a coverage rate of 10% are called "10% outlets", and the outlets with a coverage rate of 20% are called "two% outlets." Of the outlets are called "out of the net", and the outlets with a coverage rate of 100% are called "on the ground".
The tone of the printed matter is generally divided into three levels: bright tone, middle tone, and dark tone. The coverage rate of the bright tone department is about 10% ~ 30%; the coverage rate of the middle tone department is about 40% ~ 60%; the dark tone department is 70% ~ 90%. The department of net and field are divided separately.
The shape of the dots in printing is not just a circle that everyone imagines. It is divided by the shape of the dots at 50% inking rate. It can be divided into three types: square, round, and diamond.
The square dots are in a checkerboard shape at a 50% coverage rate. Its particles are relatively sharp and have a strong ability to express levels. Suitable for the performance of lines, graphics and some hard-tuned images.
Circular dots are independent between dots in bright tones or midtones. Only dark tones are connected by departments. Therefore, for the poor performance of the mining level, it is rarely used in four-color printing.
The diamond-shaped dots combine the hard tone of the square dots and the soft tone of the round dots. The natural color transition is suitable for the expression of general images and photos.
In printing plate making, the choice of dot angle plays a crucial role. Choosing the wrong dot angle will cause interference fringes.
Common dot angles are 90 degrees, 15 degrees, 45 degrees, and 75 degrees. The 45-degree dots perform best, without being cluttered and not looking stiff; the angles of 15 degrees and 75 degrees are less messy, but the visual effect is also not stiff; the 90-degree angle is the most messy, but The visual effects are too dull and have no beauty.
When two or more kinds of dots are set together, there will be mutual interference. When the interference is severe enough to affect the beauty of the image, the commonly known as "turtle" appears.
Generally speaking, when the angle difference between the two dots is between 30 degrees and 60 degrees, the overall interference fringe is still beautiful; the second is the angle difference between the dots at 45 degrees; when the angle difference between the two dots is 15 degrees and 75 degrees At this time, the interference fringes will damage the image.
Number of dots
The number of network lines determines the fineness of the image, similar to the resolution. Common line number applications are as follows:
10-120 lines: low-quality printing, posters, posters and other large-area printed materials viewed from a distance, generally printed on newsprint and offset paper, and sometimes using low-gram matte paper and coated paper.
150 lines: ordinary four-color printing generally adopts this precision, all kinds of paper are available.
175-200 lines: exquisite picture books, pictorials, etc., mostly printed on coated paper
250-300 lines: the most demanding picture books, etc., most of them are printed with high-quality coated paper and special paper.
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