Ink color matching technology (2)
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In the last issue, we have introduced a series of required equipment and the advantages and disadvantages of traditional artificial color matching. It is the best way to share the computer color matching with the new generation color matching principle.
A new generation of color theory
Database establishment
In fact, many people think that when you buy a lot of equipment, you can apply it right away. This is a wrong concept. Because the software itself is just a computer with a preset formula, how can the calculation be calculated without substituting the number into the calculation! These numbers are the ink materials we use for color matching. First, we must build a complete library of ink data. The database is the core of the entire color matching system, and all data for future calculations will be searched from this. We use the spectrophotometer to input the color of dozens of inks into the computer, and the computer converts it into visible spectrum data. The stability and accuracy of the data play an important role. If the actual material does not match the input data, then there is no The meaning is ok. Therefore, this database must be built according to the materials used by the company for daily use.
As mentioned in the previous issue, inks are produced by different companies or different regions, and their color changes and printing characteristics are different. In addition, the printing conditions used by each printing company are also different. In other words, what we do is tailor-made. Customized database. For example, the company has a large number of orders and often has to do post-process processing of varnish. In the past, the masters had to consider two factors in production:
1) Change in color tone after the print is dried
2) Change in color tone of printed matter after passing through oil
In order to balance these factors and control the quality of production, Masters often spend a lot of time and waste a lot of materials to adjust the color tone of the print. In fact, when we use computer color matching, we can take these two factors into consideration. When building a database, input a data with varnish effect. In this way, whenever a varnish effect is required, the computer will calculate the formula containing the varnish effect data, and Master will not spend a lot of resources to adjust the ink color. If the user or the customer does not have confidence in direct production, they can pre-test the test and use the IGT printability tester for pre-press testing.
Therefore, it is derived from another problem. Since the effect of varnish treatment can be expected, can the color of the paper be counted? of course can. Calculate the color of the paper and the degree of penetration of the ink, because it is considered in the color matching software whether the ink/pigment used by the user is transparent. If the printing method relies on the substrate to develop color, then when calculating the formula, it will Consider the background color of the substrate.
On the other hand, different papers have different absorption properties. However, this variable affects the results of our final print. Especially in the case of book paper, when the masters print such papers, they often worry about the change of color after the ink is dried, and often the color is much deeper than the printed sheets just produced. Therefore, the color matching system also takes this into consideration, that is, while the database is being built, it is processed separately by two types of paper (see the following figure). They are coated paper database and uncoated paper database.
In summary, the database we have established must match the needs of the plant:
Ink type
Substrate type
Post-process type
Once the complete database is complete, it can be put into production. At the same time of production, it is also necessary to consider a suitable database to prepare the target ink.
produce
Everything is ready, this time with an example to share the entire color matching process. This time, we chose to blend a grass green color (Figure 1).
First, use the spectrometer to input the color data into the software, and then click the color matching function. At this point, the computer asked us to select the database (Figure 2, A). According to the paper used for the sample, select the uncoated database of coated paper (Fig. 2, B). Then select the number of colors used (Fig. 2, C), enter the recipe window, and enter the paper materials for production.
When finished, click on the recipe operation. After a while, the computer displays the results of using different color inks to formulate the target.
If possible, the computer will calculate up to 50 recipes. Since it is possible to formulate the target color using different ink combinations, why can we choose the most suitable formula?
Selection formula
In the case of offset printing, we can rely on:
1) Delta E (DE) - color tolerance
2) Metamerism Index (MI) - metamerism index;
3) Curve Fit Index (CFI) - curve coincidence index;
4) Cost - The cost factor considers how to choose a recipe.
Color tolerance refers to the difference between the computer-calculated formula and the target standard. It is calculated under a single illumination source. The smaller the value, the higher the accuracy. However, it should be noted that it only represents the color comparison under a certain light source and fails to detect the deviation under different light sources.
The metamerism index represents the case where two samples are discolored under different light sources. In digital terms, the lower the value, the less the color change is. Considering the △E color tolerance, it is a valuable quality verification data.
The curve is consistent with the index. Colors, like humans, have their own unique indices, and spectral curves are the indices of their colors. If the spectral curves of the two samples are identical, they can be said to be the same color, CFI=0. CFI refers to the sum of the enclosed areas when the spectral curves of the two samples overlap.
Cost is a reference index that we can input at the same time when inputting ink data. When the computer calculates the formula, the formula cost is calculated together, so that the customer can consider a low-cost and desirable formula to produce.
In addition to the four reference values mentioned above, there are a number of factors worth considering, such as the Correctability Index (CRI) - Modify Index, Opacity (%OP) - opacity. Of course, the computer displays multiple indexes at the same time for the user's reference, so that the user can find the most suitable formula.
White ink and transparent ink
In general, the traditional color matching method, Master will add a lot of white ink to dilute the color concentration, or easier to control the color change when adjusting the ink; another purpose is to increase the ink hiding power, the common is to add a lot of white ink with pink or emulsified color Color, but in fact does not need to add white ink. Another advantage of computer color matching is that it can reduce the amount of white ink used, or even use it. This depends on the color of the substrate when matching colors. The use of white ink is of great benefit to the printing house. Since the white ink pigments are thicker and harder than the particles of the general ink pigments, the printing plate will be lost during production, and sometimes the printing of the ink itself will be reduced. Sex, such as abrasion resistance, drying time, etc. On the other hand, white ink is generally more expensive than transparent ink, and the cost is therefore increased, so we all recommend using a clear ink instead of white ink for color matching.
In this issue, we have briefly introduced the process of color matching. I believe that everyone has a preliminary understanding of computer color matching. The next issue will be the final summary of the remaining features and functions of computer color matching. Please pay attention.