Line and DPI

"Line" and "DPI"
For designers who enter the printing house, the understanding of line and DPI is very vague, especially for the understanding of line, even some predecessors in the printing industry, it is difficult to have an accurate understanding. In the printing industry, especially in the color printing industry, many people are at a loss how to sort out the relationship. I uncover the truth and solve the mystery for you.
In ancient times, printing should have developed from seals. Later, people made the text or pattern into a letterpress similar to a seal, painted with ink, covered with paper, and then brushed with a brush on the back of the paper to obtain the desired print, the pixels of which appeared in the form of lines or block colors.
With the development of printing, people wanted to reproduce pictures (or photographs) with tones, so there was the current dot printing, which is often called halftone printing.
Early dot printing came in the form of AM dots. It is the difference in the size of the dots and the different sizes of the dots to compose the various levels of the graded picture. These dots are the pixels that are imaged. These pixels, regardless of their size, are equally spaced apart from their centers.
From this, I conclude that the larger the dots, the larger the area covered in the same divided area, and the darker the colors we see; The smaller the dots, the smaller the area covered by the ink, and the more exposed the white background of the paper is in the same divided area, the lighter the color appears (because the center distance is equal).
Due to the difference in the size of the dots, our vision perceives the change in the color of the picture. We often say that the offset printing 175 line, that is, it is divided into 30,625 points per square inch (note: 175×175=30,625 squares), and these 30,625 points are the "pixels" that make up a square inch of the picture. The so-called 175 line refers to the division of 1 inch (length) into 175 parts, which is what we usually call "line".
DPI stands for resolution and is the number of dots scanned per inch. The resolution of the FM network generally reaches 2400dpi, that is, 2400 points can be arranged in one inch. In other words, divide a square inch of picture into 2400×2400=5760000 small squares. Resolution can also be referred to as the imaging accuracy (scanning accuracy or output accuracy) of the picture.
Since the size of the ink dots in each small square is the same, to solve the problem of the shade of the picture, the only way to distinguish between the number and the amount of ink dots is to distinguish between the number and the amount of ink dots. In a square inch, where there are many ink spots, the color is thick, and where there are few ink spots, the color is light.
In the process of computer operation, not every small square in every square inch has ink spots, but according to the intensity of each square inch to determine the number and amount of ink spots. Therefore, in the case of the same resolution, where there are more ink spots, the color coverage will be more, and the chromaticity will be darker; Where there are fewer ink spots, the color coverage is less, the white of the paper is more exposed, and the color looks lighter. These dots of ink, which make up the shades of color, are what we call the "pixels" of the FM dots.