Analysis of Common Problems in DTP Production Process

Since the DTP puts all prepress work from the original to the four-color film on the computer; since the DTP runs through everything from design to printing; due to the electronic pages described in pure mathematics on the computer, there is no alternative. This physical process of high-speed printing of ink on paper, so DTP will push computer designers to participate in the first line of printing plate.

This puts higher requirements on computer designers and requires them to require Other knowledge in addition to the professional design capabilities of the arts, especially in the printing of color separation, hanging nets, overprints, imposition knowledge, etc., in order to be able to accurately The original is faithfully reproduced.

The first one needs attention is color separation, hanging nets and other issues.

Computer designers should be aware that in the printing process, various colors are represented by superimposing different amounts of cyan, magenta, yellow, and black inks in the form of dots. As we look closely at a colorful newspaper, we can see that it consists of many points. In the darker areas, the points are larger; in the middle area, the points are moderate in size; in the lighter places, the points are smaller. However, the distance between the adjacent points is equal, and the distance between the adjacent points is determined by the screen hanging on the picture. This distance is called the number of screen lines. The number of screen lines is generally expressed as the number of one-way parallel lines per inch. The typical value of the number of screen lines used in newspapers is 80-100 lines per inch, the color prints such as magazines are 120-150 lines per inch, and the high-quality art albums are 175 lines and 200 lines per inch. In general, he stated that the resolution (dpi) of a color picture input with a scanner is based on the principle of twice the number of output screen lines. If you want to print the cover of a magazine on line 150, the dpi value of the scanned image should be 150 x 2 = 300 (dpi) during production. Therefore, the designer should first understand what the designed work is to be printed. It is a newspaper or an album to determine the dpi value of the image scan. Scan dpi value is set high, printed prints will be "paste", dpi value is too low, the work is not beautiful. The commonly used values ​​are:

Artwork carrier screen line scan dpi

Newspaper 80 -- 100 150 -- 200

Magazine 120 -- 150 250 -- 300

Photo album 175 350 350

In the four-color film, the dots of different colors are arranged at different angles so as not to overprint different colors of ink during printing. The angle between the vertical line and the horizontal line at the center of the screen is called the screen angle. These screen angles have been set in the phototypes, and they are based on a carefully selected and clever compromise: cyan is 15, magenta is 45, yellow is 90, and black is 75. Some daring designers will give up on these default perspectives and make their own choices. This should be carefully considered and trial-and-error so as to avoid the occurrence of “moiré” due to inappropriate screen angles. In order to accurately and faithfully reproduce the original, the increment of printed dots is also a problem that should be paid attention to. The so-called dot increment is a slight percentage change in the size of the dot of the printed matter compared with the dots in the original design. It is visually the depth and shade of the printed matter and the color has changed. Especially in the bright part.

The general network will generate increments in the following stages.

1) Image-setter generates dot gain on the output film

2) Exposure increments during exposure

3) Dot gain from printing ink

Of course, the type of printing machine, the type of paper is also an important factor in the creation of dot increments.

In order to obtain prints that are as faithful as possible to originals, dot gains have to be considered and overcome in designing. The increment of dots generated by the imagesetter can be overcome by regularly correcting the percentage of dots on the output film. The following set of grayscale meshes can be output regularly, measured by density, and then corrected for this set of values ​​for the imagesetter. This correction is very important.
The increment of printing outlets is about 10%. In the design, the dots to be designed should be 10% smaller than the actual outlets to be obtained in order to ensure that the printed materials can be faithful to the originals. The best method is for different printing plants. Different inks, after repeated experiments, determine the percentage increment of printing dots. And in the production of more accurate to overcome.

Percentage of mesh sites (%) 0 10 20 30 40 50 60 70 80 90 100

Density 0.00 0.05 0.10 0.16 0.22 0.30 0.40 0.52 0.70 1.00 3.50 (to be continued)