It is indeed a very troublesome problem to seek an observation environment that faithfully expresses the color of the original. An original manuscript that is undergoing production reproduction, under what environmental conditions, should the evaluation be sufficient, so that there will be no color difference?
Of course, in the production process, the best conditions for proofreading originals and reproductions are equivalent to the final observation environment of the printed matter. But all of our prints are not only copied to one customer, maybe thousands or even tens of thousands of people have access to our prints. So we have to design thousands of observation environments? It is well known that this is impossible. Because the light source changes with time and environment, the object has different coloring conditions under different light sources. If it is necessary to produce prints 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.
5000K misunderstanding
　　 Some manufacturers will say that they use the color source light source (it is already 5000K color temperature light source, why is the same 5000K light source environment to the guests, there is still error in the color of the manuscript?) We first eliminate the problem of printing quality, and then this The paragraph is split. First answer the question of the light source. In fact, 5000K only describes the color temperature of the light source, and does not represent the whole of the light source. Properly speaking, the light source emitted by the D50 standard illuminator is the light source indicator for the approved printing process. Please be sure to know that this light source must have sufficient color rendering in addition to the proper color temperature.
Let me talk about the origin of 5000K color temperature. We will heat a standard black body that can completely absorb and radiate energy. When the temperature rises gradually, the color of the light source will change accordingly. For example, the color temperature of noon daylight is 6500K, when the black body is heated to 6500K, its light source The color is equivalent to the color of the noon daylight, and we use this to quantify the color of the light source. The color temperature of 5000K is that when the black body is heated to 5000K, the color change of the light is white, and the spectral energy distribution is measured. The energy of the band in the blue, green and red regions is in an equipotential state, that is, the most ideal white light, and the color cast is the lowest. Therefore, the printing process uses a light source of 5000K color temperature, which does not emphasize which one is better than the other.
In addition, it is the problem of color rendering. Color rendering refers to the degree to which an object conforms to the color of sunlight and artificial light. The color of the object in daylight is the most accurate, because the spectral energy distribution in daylight is the most comprehensive, and it can fully express the color of the object. The color rendering index of daylight is the highest 100Ra). However, the artificial illuminating body has a large difference in spectral energy distribution depending on different materials. However, even if the illuminating body color temperature has reached 5000K artificial white light, the color of the object is different from that seen under daylight. Most of the problems are that some monochromatic light components are often missing from artificial light sources, and their color rendering index is also lower than 100Ra. The height of the color rendering index represents the distortion of the object.
However, having a high color rendering index does not mean that there is no color cast. Keep in mind that the color temperature and color rendering of the light source should match each other. The color temperature is an indicator of the color of the light source, and the color rendering is the quality index of the light. The definition of the CIE D50 standard illuminator is to standardize the quality hue of the light source.
Standard illuminator and standard light source
The CIE International Lighting Standards Association has seen that different light sources have different degrees of color effects on objects, thus specifying the following standard illuminators and specifying their spectral energy distribution.
However, the above standard illuminators can be realized by different combinations of light sources (simulated spectral energy distribution), but different materials have different stability, so CIE recommends a series of standard light sources (artificial light sources) to match the above standard lighting. body.
ISO 3664 standard observation conditions
　　 When talking about the data of so many light sources and illuminators, what is the most ideal color draft environment? In 1975, the ISO International Standards Accreditation Association has proposed "ISO 3664 to observe the lighting conditions of color transparency and reproductions" (new version is ISO 3664:2000), which refers to the observation conditions in the printing and copying process, see the following four points:
1. Spectral energy distribution of illumination source 2. Luminance and uniformity of light source 3. Observing environmental conditions—
i) Observing the environment -
Ii) Lighting 4. Stability of the lighting environment
In fact, ISO 3664:2000 has stricter requirements on lighting sources. It considers the new color imaging technology and proofing system proposed today, and also limits the problem of producing metamerism under different light sources, and on UV. The effect of photo-effects on prints is to develop this new standard. [next]
A. Illuminance
Another important factor is that it recommends two illuminance standards, which are used in the following situations:
1. High illumination 2000I ± 500lux - used to evaluate and compare images, when rigorous evaluation of prints.
2. Low illumination 500I ± 25 lux - used to distinguish image dark detail under similar final viewing conditions.
(Personally believe that high illumination is suitable for use in each print production process, while low illumination can be used when comparing the details of a single image.)
B. Observing the environment
Observing the environment may be a neglect of the printing industry. I believe you must have seen it. There are many things, posters, inks, cigarette packets, mobile phones, etc. around the observation environment in the workshop. Some of the places where the color drafts are still on the window sill Next to each other, some are more dusty, with the following tips in the ISO standard:
1. Minimize ambient interference.
2. After entering the observation environment, the printed products should not be judged immediately, so that the workers have time to adapt to the environment.
3. There should be no extra light entering the viewing range (including reflections).
4. There should be no strong colors around the (worker's overalls).
5. The surrounding area of ​​the observation range should be a neutral gray dull and a color block with a reflectance of less than 60%.
In fact, the above are all issues that the printing factory should pay attention to. These conditions are just a signal that can be implemented, which not only improves the environment of the manuscript, but also improves the quality of production and enhances the professional image in the factory.
The standard observation environment mentioned in ISO 3664:2000 is full of words. The above is just a few words. If the manufacturers are interested in improving the observation environment, please visit the ISO website and download the relevant documents of the standard. reference.
How to choose the right light source equipment
　　 The easiest way is to buy a light box that complies with ISO standards. Of course, if you pay for a penny, the small ones will generally cost more than 10,000 yuan, while the large ones will cost 30,000 yuan. How can the printing factory invest? However, in addition to meeting the ISO requirements, this type of color evaluation light box has a variety of light sources, such as D65, D50, UV, TL84, A, etc., suitable for different industrial needs. Interested manufacturers can visit the Print Materials Testing and Analysis Center. It is because of the relationship between the amount of investment that many manufacturers considering purchasing are deterred, and then they are looking for someone to order. We can also ask for some suitable materials to match the homemade light box.
1. Light pipe - There are many brands of light pipes on the market that indicate a total of 5000K (unfortunately, CIE has not yet specified the standard light source application of D50 standard body), but it does not necessarily meet the requirements specified by ISO, so we should pay attention to the following point:
i) Color temperature - 5000K
Ii) Color rendering index - ≧90Ra
Iii) Illumination - illuminance depending on the evaluation space (lux): lumens / square meter (Note: general light pipe label only indicates its lumens)
2. Panel material - as long as it can be close to the ISO restrictions such as:
i) The chromaticity is neutral ash - the color index of the surface of the material can be measured by a spherical spectrodensitometer, close to Lab -50,0,0
Ii) Reflectance - measure its reflectance by gloss meter ≦ 60%
test method
It is generally sufficient to measure the change in color temperature during production because the stability of the illuminator changes with time and environment. Although there are color temperature meters available on the market (purchased by professional photographic equipment companies), the price is not cheap, there is a cheaper way to check the color temperature on a daily basis, like a sticker called GATF/RHEM (made by GATF), When we put the indicator in the observation environment, when the color temperature changes, it will warn the operator whether it needs to replace the light pipe.
Conclusion
The complexity of the color printing process is well known. The production of a piece of printed matter is often completed in a dozen steps. The company, the staff involved, etc., have different evaluations of the printed matter in different environments and at different times. Therefore, we can only give the printer a subjective evaluation by limiting the external factors such as the environment. This is fair and objective, so as to reduce the disputes caused by the environment. Therefore, the standard lighting environment, the light source is a must. I hope that you can consciously improve and standardize your observation equipment.
It is indeed a very troublesome problem to seek an observation environment that faithfully expresses the color of the original. An original manuscript that is undergoing production reproduction, under what environmental conditions, should the evaluation be sufficient, so that there will be no color difference?
Of course, in the production process, the best conditions for proofreading originals and reproductions are equivalent to the final observation environment of the printed matter. But all of our prints are not only copied to one customer, maybe thousands or even tens of thousands of people have access to our prints. So we have to design thousands of observation environments? It is well known that this is impossible. Because the light source changes with time and environment, the object has different coloring conditions under different light sources. If it is necessary to produce prints 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.
5000K misunderstanding
　　 Some manufacturers will say that they use the color source light source (it is already 5000K color temperature light source, why is the same 5000K light source environment to the guests, there is still error in the color of the manuscript?) We first eliminate the problem of printing quality, and then this The paragraph is split. First answer the question of the light source. In fact, 5000K only describes the color temperature of the light source, and does not represent the whole of the light source. Properly speaking, the light source emitted by the D50 standard illuminator is the light source indicator for the approved printing process. Please be sure to know that this light source must have sufficient color rendering in addition to the proper color temperature.
Let me talk about the origin of 5000K color temperature. We will heat a standard black body that can completely absorb and radiate energy. When the temperature rises gradually, the color of the light source will change accordingly. For example, the color temperature of noon daylight is 6500K, when the black body is heated to 6500K, its light source The color is equivalent to the color of the noon daylight, and we use this to quantify the color of the light source. The color temperature of 5000K is that when the black body is heated to 5000K, the color change of the light is white, and the spectral energy distribution is measured. The energy of the band in the blue, green and red regions is in an equipotential state, that is, the most ideal white light, and the color cast is the lowest. Therefore, the printing process uses a light source of 5000K color temperature, which does not emphasize which one is better than the other.
In addition, it is the problem of color rendering. Color rendering refers to the degree to which an object conforms to the color of sunlight and artificial light. The color of the object in daylight is the most accurate, because the spectral energy distribution in daylight is the most comprehensive, and it can fully express the color of the object. The color rendering index of daylight is the highest 100Ra). However, the artificial illuminating body has a large difference in spectral energy distribution depending on different materials. However, even if the illuminating body color temperature has reached 5000K artificial white light, the color of the object is different from that seen under daylight. Most of the problems are that some monochromatic light components are often missing from artificial light sources, and their color rendering index is also lower than 100Ra. The height of the color rendering index represents the distortion of the object.
However, having a high color rendering index does not mean that there is no color cast. Keep in mind that the color temperature and color rendering of the light source should match each other. The color temperature is an indicator of the color of the light source, and the color rendering is the quality index of the light. The definition of the CIE D50 standard illuminator is to standardize the quality hue of the light source.
Standard illuminator and standard light source
The CIE International Lighting Standards Association has seen that different light sources have different degrees of color effects on objects, thus specifying the following standard illuminators and specifying their spectral energy distribution.
However, the above standard illuminators can be realized by different combinations of light sources (simulated spectral energy distribution), but different materials have different stability, so CIE recommends a series of standard light sources (artificial light sources) to match the above standard lighting. body.
ISO 3664 standard observation conditions
　　 When talking about the data of so many light sources and illuminators, what is the most ideal color draft environment? In 1975, the ISO International Standards Accreditation Association has proposed "ISO 3664 to observe the lighting conditions of color transparency and reproductions" (new version is ISO 3664:2000), which refers to the observation conditions in the printing and copying process, see the following four points:
1. Spectral energy distribution of illumination source 2. Luminance and uniformity of light source 3. Observing environmental conditions—
i) Observing the environment -
Ii) Lighting 4. Stability of the lighting environment
In fact, ISO 3664:2000 has stricter requirements on lighting sources. It considers the new color imaging technology and proofing system proposed today, and also limits the problem of producing metamerism under different light sources, and on UV. The effect of photo-effects on prints is to develop this new standard. [next]
A. Illuminance
Another important factor is that it recommends two illuminance standards, which are used in the following situations:
1. High illumination 2000I ± 500lux - used to evaluate and compare images, when rigorous evaluation of prints.
2. Low illumination 500I ± 25 lux - used to distinguish image dark detail under similar final viewing conditions.
(Personally believe that high illumination is suitable for use in each print production process, while low illumination can be used when comparing the details of a single image.)
B. Observing the environment
Observing the environment may be a neglect of the printing industry. I believe you must have seen it. There are many things, posters, inks, cigarette packets, mobile phones, etc. around the observation environment in the workshop. Some of the places where the color drafts are still on the window sill Next to each other, some are more dusty, with the following tips in the ISO standard:
1. Minimize ambient interference.
2. After entering the observation environment, the printed products should not be judged immediately, so that the workers have time to adapt to the environment.
3. There should be no extra light entering the viewing range (including reflections).
4. There should be no strong colors around the (worker's overalls).
5. The surrounding area of ​​the observation range should be a neutral gray dull and a color block with a reflectance of less than 60%.
In fact, the above are all issues that the printing factory should pay attention to. These conditions are just a signal that can be implemented, which not only improves the environment of the manuscript, but also improves the quality of production and enhances the professional image in the factory.
The standard observation environment mentioned in ISO 3664:2000 is full of words. The above is just a few words. If the manufacturers are interested in improving the observation environment, please visit the ISO website and download the relevant documents of the standard. reference.
How to choose the right light source equipment
　　 The easiest way is to buy a light box that complies with ISO standards. Of course, if you pay for a penny, the small ones will generally cost more than 10,000 yuan, while the large ones will cost 30,000 yuan. How can the printing factory invest? However, in addition to meeting the ISO requirements, this type of color evaluation light box has a variety of light sources, such as D65, D50, UV, TL84, A, etc., suitable for different industrial needs. Interested manufacturers can visit the Print Materials Testing and Analysis Center. It is because of the relationship between the amount of investment that many manufacturers considering purchasing are deterred, and then they are looking for someone to order. We can also ask for some suitable materials to match the homemade light box.
1. Light pipe - There are many brands of light pipes on the market that indicate a total of 5000K (unfortunately, CIE has not yet specified the standard light source application of D50 standard body), but it does not necessarily meet the requirements specified by ISO, so we should pay attention to the following point:
i) Color temperature - 5000K
Ii) Color rendering index - ≧90Ra
Iii) Illumination - illuminance depending on the evaluation space (lux): lumens / square meter (Note: general light pipe label only indicates its lumens)
2. Panel material - as long as it can be close to the ISO restrictions such as:
i) The chromaticity is neutral ash - the color index of the surface of the material can be measured by a spherical spectrodensitometer, close to Lab -50,0,0
Ii) Reflectance - measure its reflectance by gloss meter ≦ 60%
test method
It is generally sufficient to measure the change in color temperature during production because the stability of the illuminator changes with time and environment. Although there are color temperature meters available on the market (purchased by professional photographic equipment companies), the price is not cheap, there is a cheaper way to check the color temperature on a daily basis, like a sticker called GATF/RHEM (made by GATF), When we put the indicator in the observation environment, when the color temperature changes, it will warn the operator whether it needs to replace the light pipe.
Conclusion
The complexity of the color printing process is well known. The production of a piece of printed matter is often completed in a dozen steps. The company, the staff involved, etc., have different evaluations of the printed matter in different environments and at different times. Therefore, we can only give the printer a subjective evaluation by limiting the external factors such as the environment. This is fair and objective, so as to reduce the disputes caused by the environment. Therefore, the standard lighting environment, the light source is a must. I hope that you can consciously improve and standardize your observation equipment.
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