In the previous standard, the matching degree was specified using the CIE's color rendering index. It reflects the degree of similarity between the color of a series of standard color patches under the theoretical D50 light source and the display color under the actual observation light source.
If the color we're dealing with has a spectral emission curve, and the UV Polishing effect page doesn't affect it, then we can use the 1795 standard without changing it.
Currently, color imaging and proofing systems use many new technologies in the creation of images: dye sublimation, thermal transfer, inkjet, electrostatic imaging, and more. The use of these methods is gradually increasing the color contrast of the image. Most of the primary fuels used in these technologies are matched with photos or inks to print color effects, and their reflection curves will have abrupt changes in some places relative to their matching color curves. This is called metamerism. The negative effect of metamerism matching is that the color is very sensitive to changes in lighting conditions. In this way, it is not enough to use the color rendering index to describe the characteristics of the light source.
The new standard retains the feature of color rendering index while adding two new standard parameters: visibility and UV discoloration index. These two indices are from the CIE Edition Standard No. 51, 1981 - Methods for evaluating the quality of light sources. These parameters use more sophisticated matching criteria. A calibration may, as the case may be, calibrate the UV portion of the spectrum to more strictly distinguish the actual light source from the CIE D50 ideal illumination.
That is, if the new standard is met, the observation device will provide more stable observation conditions. This will reduce problems that arise from the sensitivity of new materials or fluorescent lights to paper and ink.
Preliminary tests showed that most of the observing equipment considered to be better in the old standard also conformed to the new standard. Equipment that was defined by standards in the early days may have many problems and need to be updated so it is not feasible to explain which recommended indicator is feasible, and those who need further work.
A light source indicator called GATF/RHEM can warn the observation environment when the observation conditions are not correct. It is very convenient if the device is directly assembled under working conditions to remind the staff to observe the environment. However, it should be noted that GATF/RHEM cannot explain the correctness of observation conditions.
Two new illuminances are recommended in the new luminance level standard, with high illumination (P1) 2000+-500lx for use in evaluating and comparing images; low illumination (P2) 500+-25lx for simulating similar and final viewing conditions Tonal observation. Changes in the evaluation and comparison of early standards are necessary. For example, comparing the effect of originals and proofs, or comparing subtle color differences between identical sheets and printed images during the printing process, applies to this recommendation.
Thus, despite the fact that the observation conditions have a certain degree of adaptation, the change in the illumination level has a very significant effect on the performance of the image. To simulate the final image viewing environment, use the recommended low light level (P2). Although the lighting conditions in the daily observation process are also changing, the choice of the standard illumination conditions is the most typical lighting situation that we usually observe.
In the industry, the recommendation of low-light level should be highly controversial. It has been suggested that too much illuminance recommendation may cause confusion. So, after the standard, the following hints are attached for explanation:
Note: When “emphasizing the details of image comparisons†is performed at a higher illuminance than usual observations, this will facilitate the observation of nuances between images. For example, a combination of the same sheet and a printed sheet can be easily distinguished. Therefore, the quality comparison of all two or more images must be performed under P1 conditions. However, it is better to perform the tone reproduction and the actual quality evaluation of a single image under the conditions consistent with the final observation conditions. This is consistent with the reader's observation of the image. However, we may not know what the final observation conditions are. Without understanding the quality of the final observation,...
2 conditions meet this condition.
Mr. David McDowell (one of the authors) believes that the following practical problems should be emphasized: "I have recently observed the same image in several different lighting conditions. The picture includes a very delicate lace, The color is very close to the background.My observation under the standard observation table is not as good as the effect in the office environment.The very beautiful image seen in the office is pale when viewed under the observation table, just like water soaked After some time, I met an advertisement drawing about a large-scale wholesale process.The picture was colored, the content was a picture of a black lawn construction worker and lawn mower against a black background.My first reaction was that How can this kind of image be reproduced? We can hardly see anything above, but when I look under the standard observation table, even the shadows of the images can be resolved without any problem. Maybe we also often come across this kind of image. Situation, try to pay attention."
In addition to viewing the matching of the copied image with the original on the observation platform, we can also observe the image in a hall, office or other low light place. This change in lighting conditions cannot be controlled in terms of brightness levels or color characteristics. If we are using this kind of changing lighting for proofing, especially for some new materials, we will be forced to adjust the color effect of the image. Therefore, specifying a low-lighting observation condition suitable for both high-brightness observation conditions (2000lx) and low-illumination observation conditions will be a very favorable thing. In this way, the tone reproduction effect of the image will be judged more realistically. More importantly, we can simulate this observation condition in other places to obtain the same observation effect.
The standards also specify the observation criteria for the transmitted and projected drawings. For direct observation, the central illumination of the transmitted document illumination should be 1270cd/m2+-cd/m2, and the surrounding environment should be provided with a neutral gray state at least at an area 50mm wide from each side, and the illuminance should not exceed 10% of the image observation plane. If the translucent document has an opaque border, there is no need to remove the border.
Observing the environment During the observation, the surrounding conditions also have a great influence on the observation effect. In the new standard, the following conditions are prompted:
1. The observation environment should minimize the interference of image observation. In order to avoid other conditions affecting the judgment of the transmitted document or the printed matter, it is necessary to avoid immediately starting the evaluation after entering the observation environment. The human eye needs at least a few minutes to adapt to the environment.
2. Extra light, whether emitted from other light sources or reflected from the surface of other objects, affects observation or other image lighting.
3. In the observation environment at that time, there should be no intensely colored surfaces (including clothing).
Note: Observing strong colors in the market is a potential problem because they may produce unavoidable reflections. Reflective ceilings, walls, floors, or other surfaces in the field of view may discolor the neutral gray block with less than 60% reflectivity.
The new standard also states that the surrounding environment with neutral light and no light on the edge of observations should extend at least 1/3 of the observation space on all sides. The reflectance of the surrounding environment is less than 60%, preferably less than 20%. The new standard also states that the contrast image should be placed on the opposite side.
Maintain the stability of the light source In general, observers do not have corresponding test equipment to test the distribution of illuminance and spectral energy on the observation platform. So the routine use of the observation environment maintenance method is to replace the bulbs regularly. The standard states that the manufacturer should explain the shelf life of the equipment or instrument and remind the user to perform maintenance on schedule unless the user has sufficient reason to explain that the equipment is in normal working condition. It recommends that the observation equipment be equipped with appropriate time-of-use test equipment or other instruments with attenuation indicators. Some manufacturers use the lamp for 2500-5000 hours a year to illustrate the use of the lamp. However, it has not been proposed that the observation table should be kept clean and tidy.
Display viewing conditions The industry has not recommended any conditions for viewing images on the display. If people do not need to rely on the on-screen display to judge the final image, it will not be a problem. We do not have to argue whether the observation method is feasible. However, in order to obtain stable observations, it is necessary to provide a stable observation condition. The new standard includes standard screen observations that differ from any other form of copy. Of course, the specified observation conditions should be effective for simultaneous observation of hard-copy images or screen images. Another standard, ISO12646 "Standards for Color Profiling Using Color Displays for Printing Technology," is under development. It was developed by ISO's Graphics Technology Association TC130 and includes more recommendations on the details of observations for direct screen comparison of images.
ISO 3664 includes the following instructions for monitor viewing:
1. The white color of the display screen is close to the standard of D65; the brightness of white must be greater than 75cd/m2, generally greater than 100cd/m2.
2. For any display or observation surface, the ambient illumination should be less than 64lx, preferably less than 32lx. The ambient lighting color temperature must be <= the color temperature of the monitor's white point.
3, the area around the display image should be neutral, preferably the lowest flicker of gray or black, chroma value close to the white point of the display.
4. The monitor must be placed in an area of ​​observation without strong color reflections (including clothing). Because strong colors may reflect on the display. Ideally, all walls, floors, and furniture in the business should be grey or free of placards, signage, images, text, or other effects that are observable.
5. Other light sources or spots should be avoided in the environment. Because they have caused a reduction in image quality. The display should be left without direct lighting, windows, etc.
For a light source with a correlated color temperature different from 5000K, the color rendering index and the color rendering index specified in the standard do not apply. In this state, the user must understand the similarity of the spectral distribution of the tungsten lamp with the theoretical full radiator. If the spectral distribution is very close, the chromaticity, conditional color tea, and color rendering will be very close.
Other content ISO 3664 also includes test conditions and experimental data on the validity of the certification standard.
Because "in the process of judging the content of an image or displaying a picture, a person's subjective impression is a very important criterion for judgment." This standard includes an appendix "Standard for observing and displaying pictures."
(This standard applies to both prints and color photos). Table 2 lists the recommended conditions for viewing conditions in this appendix.
Table 2 Recommendations: Observation Conditions for Observations and Exhibition Pictures
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