Analysis of Factors Affecting the Quality of Greeting Cards Printing by Observation Conditions

Analysis of Factors Affecting the Quality of Greeting Cards Printing by Observation Conditions

Observation conditions

　　 The appearance and color of Greeting Cards printed matter and other objects are largely affected by the observation conditions. Therefore, all judgments on color must be made under repeatable conditions. To achieve this goal, everyone involved in color reproduction must use standard observation conditions. The term "standard observation conditions" refers to an environment in which the following conditions must be carefully controlled:

　　●The color of the light source

　　 The intensity of the light source

　　●The influence of spectral reflectance

　　●Ambient color

　　●The influence of non-standard ambient light sources

　　●Visual adaptation of the observer

　　The environment that meets the above conditions can be obtained through the equipment designed and provided according to ISO3664. Observation racks or observation decks require regular maintenance to ensure that their conditions meet the standards to be maintained. The maintenance schedule should include the following tasks:

　　●All neutral-colored surfaces, fluorescent tubes and partitions should be cleaned at least once a month, and the cleaning materials used should not cause damage to these surfaces.

　　●Fluorescent tubes should be replaced after 2000 hours of use.

　　 The color temperature of the light source under standard observation conditions is 5000K. Some people suggest that the user’s observation conditions are more appropriate. There are two important reasons that make this impractical:

(1) It is impractical to combine every possible light source. (2) The goal of many printed materials is to coordinate cooperation and synchronize input. This input comes from people with different divisions of labor, who are in their respective companies or even their respective countries. , Thus having a different environment. Standard observation conditions ensure that all participants, no matter where they are evaluated, can be consistent with the environment at the starting point.

The only non-standard lighting conditions that should be used is when the observation conditions of the main environment have been determined and controlled. A typical example of such conditions is in retail locations, such as supermarkets, for packaging or display materials reserved for supermarkets or shopping malls. The final assessment should be carried out under the lighting conditions related to the shopping mall environment.

　　 For many printing companies, seeking an observation environment that can faithfully express the color of the original manuscript has identified a very troublesome problem. A manuscript that is being copied in production, what kind of environmental conditions must be inspected to make the evaluation standard enough so that there will be no color difference?

　　The light source changes with time and environment. Objects have different color rendering under different light sources. If you want to produce printed matter suitable for observation under different light sources, cost and manpower will cause unnecessary waste. Therefore, we must develop an objective and standard environment to ensure that uniform observation conditions can be used throughout production. [next]

　　 5000K misunderstanding

　　Some manufacturers say that the light source they use for the color correction is already 5000K color temperature light source. Why does the color of the manuscript still have an error when the light source environment of 5000K is also used by the guests? In fact, 5000K only describes the color temperature of the light source, and does not represent all the light source. Correctly speaking, the light source emitted by the D50 standard illuminator is the recognized light source indicator for the printing process. Everyone must be clearly aware that in addition to the appropriate color temperature, the light source must have sufficient color rendering.

Let’s talk about the origin of the 5000K color temperature. We heat a standard black body that can completely absorb and radiate energy. When the temperature gradually rises, the color of the light source will also change. The 5000K color temperature is to heat the black body to 5000K. When the light color changes to white, and the spectral energy distribution is measured, the band energy in the blue, green, and red regions is in an isoenergetic state, that is, the most ideal white light with the lowest color cast, so this type of light source is used in the printing process.

  in addition. It is the issue of color rendering. Color rendering refers to the degree of color matching of an object under sunlight and artificial light sources. The color of an object in sunlight is the most accurate, because the spectral energy distribution in sunlight is the most comprehensive, and it can also fully express the color of the object (this The color rendering index of daylight is the highest at 100. However, due to different materials, the spectral energy distribution of artificial lighting is still very different from that of daylight. However, even if the color temperature of the illuminating body has reached 5000K artificial white light, the color of the object is still the same as that of daylight. Seen below is different. Most of the problems are that artificial light sources often lack certain monochromatic light components, and their color rendering index is also lower than 100. The level of the color rendering index represents the distortion of the object. But there is A high color rendering index does not mean that there is no color cast. The color temperature and color rendering of the light source must cooperate with each other. The color temperature is an indicator of the color of the light source, and the color rendering is an indicator of light quality. The CIE D50 standard illuminating body is set, that is It shows that the quality and hue of the light source should be standardized.

　　Standard illuminator and standard light source

　　 CIE International Lighting Standards Association has different degrees of color influence on objects according to different light sources, so it stipulates the following standard illuminators and specifies their spectral energy distribution.

　　 However, the above-mentioned standard illuminating body can be realized by different light source combinations (simulating spectral energy distribution), but different substances have different stability, so C! E recommends a series of standard light sources (artificial light sources) to match the above-mentioned standard illuminators. [next]

　　ISO3664 standard observation conditions

　　 Speaking of so many light sources and lighting materials, what is the most ideal environment for color matching? The ISO International Standards Certification Association has proposed "ISO3664 Illumination Conditions for Observation of Color Perspective Films and Reproductions" (the new version is ISO3664: 2000), which mentions the observation conditions in the printing and reproduction process, see the following four points: 1. Illumination light source The spectral energy distribution of the light source, 2. The degree and uniformity of the light source, 3. Observe the environmental conditions, 4. The stability of the lighting environment.

　　In fact, ISO3664:2000 has more stringent requirements for lighting sources. It takes into account the new color imaging technology and drafting system proposed today. It also limits the problem of metamerism of materials under different light sources and formulated this standard.

　　 Illuminance

　　Another important factor is that it recommends two illuminance standards to be used in the following situations:

　　1. High illumination 20001±500IUX-used to evaluate and compare images, when strictly evaluating printed products.

　　2. Low illumination 5001±25IUX-used to distinguish the dark details of the image under similar final observation conditions.

　　 observe the environment

The observation environment may be a neglected part of the printing industry. I believe you must have seen it. There are a lot of things around the observation environment in the workshop, such as posters, ink, cigarette packs, mobile phones, etc., and some color drafts are still on the windowsill. Some of the neighbors are more dusty, and there are the following tips in the ISO standard:

　　 1. Minimize the surrounding environment interference.

　　 2. After entering the observation environment, the printed products should not be judged immediately, so that workers have time to adapt to the environment.

　　 3. No extra light should enter the observation range (including reflection).

　　 4. There should be no strong colors around (workers' overalls).

　　 5. The periphery of the observation range should be a color patch with neutral gray matt and reflectivity less than 60%.

　　 In fact, the above mentioned are all issues that the printing plant should pay attention to. These conditions are just a signal. Being able to implement it can not only improve the drafting environment, but also improve the quality of production and enhance the professional image of the plant. [next]

　　How to choose the right light source equipment

　　The easiest way is to buy a light box that meets the ISO standard. In addition to meeting the requirements of iSO, there are also a variety of light sources to choose from, such as D65, D50, UV, TL84, A, etc., which are suitable for different industrial needs. The following points can be referred to when purchasing:

　　 1. There are many brands of light tubes on the market that indicate that it is 5000K (unfortunately, CIE has not yet stipulated the standard light source application for D50 standard photographs), but they may not meet the requirements specified by ISO: color temperature 5000K, color rendering index ≥9.

2. As long as the panel material can be close to the ISO limit, such as the chromaticity is medium gray-the color index of the surface of the material can be measured by a spherical spectrodensimeter, which is close to Lab-50, 0, 0, and the reflectance is measured by a gloss meter. The reflectivity is 60%.

  test method

　　 It is generally sufficient to measure the change of color temperature during production, because the stability of the illuminating body will change with time and environment. There is a cheaper way to check the color temperature on a daily basis, a sticker called the light source labeling sticker (GATF/RHEM) (produced by GATF, sold by the Hong Kong Graphic Arts Society), when we put the indicator in the observation environment, when the color temperature changes It will warn the operator if it is necessary to replace the light pipe. [next]

　　 Metamerism in color printing

　　 Metamerism is a common phenomenon in nature. Simply put, it refers to colors that look the same in appearance, but whose spectral composition is not the same. In other words, the two color samples have different spectral reflectance curves, but have the same visual effect under a certain light source.

　　 Metachromatic colors are common in the field of color reproduction, and often encounter color matching problems in work, that is, the same color as the sample is required. It is difficult to achieve the same color appearance and the same spectral characteristics, so most of them are metachromatic colors.

　　The color materials used in the color printing process cannot be exactly the same as the color materials used in various color manuscripts, such as Chinese painting pigments and watercolor paints used in various painting manuscripts. Therefore, the process of color printing and copying uses the phenomenon of metachromatic color to achieve the purpose of color reproduction.

　　 Metamerism is conditional, it must be under the same observation conditions, mainly the same light source. Experiments show that the two metachromatic colors no longer maintain the same color due to changing the lighting source. In most cases, accurate metamerism color matching is difficult to achieve, and generally only approximate metamerism matching can be achieved. In color printing, there will be a certain color difference when the three primary colors are mixed with spot color inks or the three primary colors are overprinted to reproduce various colors. In actual production, the color difference between the reproduction and the manuscript should be allowed when doing metachromatic matching, but as a reproducer, the color difference should be controlled as far as possible within the allowable range specified by the standard.