Simulated proofing is a technique for simulating the printing process in the prepress field, which requires a certain amount of experience. In particular, the proofing machine is manually filled with ink and adjusts the amount of water. The printing pressure of the proofing machine needs to be adjusted by an experienced operator. So the editor will take you to discuss what are the main data indicators that affect the quality of proofing?
The main data indicators that affect the quality of proofing are as follows:
Proofing Solid Density Proofing solid density reflects the condition of paper receiving ink. When the ink is transferred from the printing plate to the blanket, and then the blanket is pressed onto the paper, part of the ink is absorbed by the paper fibers, and the other part of the ink will form the film surface of the ink layer on the surface of the paper. When offset paper is used as horse paper for printing, the paper absorbs more ink due to its looser fibers.
Therefore, the amount of ink required during printing will increase, and the film surface of the ink layer formed on the paper surface will become thinner. In addition, the surface smoothness of offset paper is low, so even if it absorbs more ink, the reflection density of the ink will not be very high. Under normal circumstances, we all use the ink reflection density on coated paper as the data control standard for proofing density.
The optical reflection density of yellow, magenta, cyan and black inks in the normal range is: yellow 9-1.1; magenta 1.3-1.4; cyan 1.5-1.6; black 1.8-1.9.
The above control data should ensure that the normal outlet status is valid during proofing. In the case where the dot state is not ideal, the ground density is meaningless. At the same time, the brands of inks used are different, and their reflection densities are also different. Under normal circumstances, if the hue purity of the ink is high, the reflection density of yellow, magenta, and cyan can be set lower.
Proofing network expansion value
Since the simulated proofing is to simulate the printing state of the printing press, it is a round flattening printing method after all. Even if the printing pressure is not as great as that of a printing machine during ink transfer, it still has printing pressure, so inevitably there is dot expansion. The dot expansion will vary depending on the paper. Due to the large amount of printing ink required for offset paper, and in order to adapt to the phenomenon of rough and loose surface structure of offset paper, the viscosity of the ink must be reduced. The ink with low viscosity and large amount is transferred to the PS plate and blanket, and when it finally reaches the paper, it will eventually cause the dot area to expand. Therefore, when offset paper is used as proofing paper, the dot expansion value is 20%.
The dots will expand excessively due to abnormal changes in printing pressure, blankets, etc. However, it is difficult to observe whether the expansion of dots meets the standards of data control with a magnifying glass. Therefore, it is beneficial to select the relative contrast value-K value as the method of measuring the expanded value of the proof dots. The expansion value can reflect the change state of the outlet in the area 75 which is easy to expand. Thus, it can representatively reflect the expanded state of the outlets. The larger the value of K, the better the dots in the dark areas. During the proofing process, the damage caused by the expansion of the dots will be the most serious in the dark and middle tone areas. The calculation formula of K value is:
K = field density- (75 density)
Field density When using 157g coated paper for proofing, the best data for the relative contrast value K of the yellow, magenta, cyan, and black plates is between 0.4-0.6. Controlling the K value to a higher value as much as possible is advantageous for reflecting the dark tone level of the picture.
Hue and purity of proofing ink
The hue of the proofing ink is directly related to the neutral gray balance and color formation. At present, four-color fast-drying inks for lithographic printing in China can be roughly divided into two sets of standards: one set is medium yellow, magenta, sky blue, and black; the other set is transparent yellow, magenta, sky blue, and black.
In these two sets of inks, magenta and magenta are the main differences. In some pictures with red as the main tone, as well as skin tones and large red areas, two different situations will appear: printing in magenta will show bright red, while the skin tone area, it is not a little more or less like magenta One point will be particularly sensitively reflected; when using a magenta set of inks, the magenta curve will exist in the neutral balance curve slightly higher than the yellow curve.
The difference between medium yellow and transparent yellow ink is that the medium yellow ink has a weak hiding power. Therefore, it is advantageous to express the color in the last color overprint when using it, which is also in line with the printing color sequence of the four-color machine.
When printing with different inks, there will be differences in the formation of color in the same dot area, so the balance of neutral gray will also bring difficulties to the scan quality and data. For this reason, under normal circumstances, the proofing operation always uses a set of inks, and will never arbitrarily change the brand and model of the proofing ink.
At the same time, in the process of color formation, the ink will also affect the normal performance of the color of the printed matter due to its purity. The main reason for affecting the purity of the ink during the proofing process is that: during the color changing process of the proofing machine, the ink roller is not cleaned, so that the hue of the ink is affected by the residual ink of the previous color. Therefore, it is very necessary to maintain the original hue and purity of the ink during the operation. It is an effective method to control the hue of the ink by using the reflection densitometer to measure the relevant data of the ink. Measure the density of the other two colors of pure ink with the standard three-color filters of reflection densitometer R, G and B. Actually, the hue error of the ink is calculated based on the data obtained from three different color filters of one color ink , Grayscale and color efficiency. However, in the actual operation process, in order to facilitate the operation, as long as the minimum density of the two color filters is controlled, the purity of the hue of the ink can be controlled. When measuring cyan ink, use G and B filters; when measuring yellow ink, use R and G filters; when measuring magenta ink, use B and R filters.
Simulated proofing is a technique for simulating the printing process in the prepress field, which requires a certain amount of experience. In particular, the proofing machine is manually filled with ink and adjusts the amount of water. The printing pressure of the proofing machine needs to be adjusted by an experienced operator. At the same time, in the proofing process, it is necessary to use a reflection densitometer and a high magnifying glass to control the ink density and dot quality to ensure the stability and accuracy of the proof. The table above shows the disadvantages and causes in the proofing process.
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