Standard observation conditions in printing The latest ISO 3664 introduction

Color and density measurements are common methods for controlling copy quality in printing. But for an image, these related test methods cannot replace the human eye's ultimate evaluation of the effect of color quality reproduction. In print copying, we mainly compare the copy images with various graphic plaintiffs to determine the degree of reduction of color reproduction. For example, in the evaluation of the color quality of a duplicated color image, a common method is to compare the original image with the plaintiff's loyalty degree.
Undoubtedly, the best observation conditions for controlling the reproduction of printed materials in the printing process should be consistent with the final observation environment of the printed products. If the final observation environment is very clear, the quality of printed matter can be monitored under the same conditions. However, this situation is generally not possible. It is particularly important that the final observation conditions do not allow us to make direct comparisons between the originals, photographs, or the same sheets and final printed items. Because in the light source and related observation conditions, the color of each material directly affects the final image effect. Their performance is often different. In order to avoid misunderstanding of the effect of color reproduction, it is necessary to use stable observation conditions during product reproduction.
Observing the surroundings of the environment or the surface of existing objects, their color and brightness pages greatly influence the viewer's perception of the node's color perception. Advantages, people use the standard observation box for observation. But the general observation deck is in some part of the house. Therefore, the control of the observation environment is very important.
In order to ensure the use of uniform observation conditions in all replication links, it is imperative to recommend uniform observation standards. For viewing conditions for color prints and photos, the recommended standard is ISO 3664. The latest version will be launched in 1999.
Prior to the introduction of the new standard, there have been two standards, the 1975 “Illumination Conditions for Observing Color Photography and Reproductions of ISO 3664” and ANSI “PH2.30-1989 Print, Photo, Color Print, Projection Laser Image Replica. Observation conditions." They are very similar in their recommendations for observation standards, but they are not exactly the same. The revision of the new ISO 3664 standard began in late 1994. The ANSI Association stated that the standard for zinc is ANSI.
In the printing and copying process, to ensure stable and consistent observation conditions, there are several key factors:
1. The spectral energy distribution of the illumination source 2. The luminous intensity and uniformity of the illumination source 3. Observe the environmental conditions (including the observation environment and the lighting environment)
4. Stability of the lighting environment The new version of ISO 3664 includes all the required recommendations. At the same time, the zinc plate standard also makes recommendations for image observation on a color screen, and the conditions for picture display and appreciation. This standard will also be used in the printing press industry.
Table 1 describes the key items in the observation standard of ISO 3664.
(1) This parameter is recommended to define the light energy distribution of the light source other than the reference display of the color display, and the color display tolerance of the white point is specified in parentheses. These instructions are based on visual observations of the 1976u'10'10 UCS system.
(2) The ratio of the illuminance of the transmitted light source to the illuminance of the observation plane of the equivalent print is 2 (+-.2):1 when comparing the transmitted text with the printed article.
(3) The ambient lighting of the color display should be less than or equal to 32 lx, and generally <= 64 lx can be used.
Calibration of Light Sources This standard recommends basic observation lighting as the CIE D50 standard light source, which actually assigns the lighting to a spectral distribution with a correlated color temperature of 5000K. It is said that one of the reasons for using D50 initially was that his energy distribution in the blue, green, and red bands of the spectrum was nearly equal. Manufacturers of light sources have tried their best to use a variety of materials for fluorescent lamps and color filters to obtain light sources with D50 effects. However, it is the illuminant effect of focusing and not having a lamp that perfectly matches the CIE standard illumination body D50. Therefore, the corresponding parameters are recommended in the standard to compare the actual observation light source with the theoretical light source. Table 1 Specified viewing conditions in ISO ISO viewing conditions Reference lighting and color difference (1)
Illumination color rendering index (according to CIE13.2 standard)
Metameric index (according to CIE51)
Lighting uniformity (min:max)
Ambient lighting reflectance/illuminance/luminance identification of prints Comparison conditions (PI)
D50 standard light source (0.005)
2000 lx+-500 lx (ideally +-250 lx)
Conventional index:>=90 Specified index of 1-8: >=80
Visual effects: C or better: Ideally B or better UV: Plane above 1mX1m>=0.75 Plane over 1mX1m>=0.6
Transmission Direct Observation (TI)
D50 standard light source (0.005)
1270+-320 cd/m^2 (ideally 160cd/m^2) (2)
Conventional index:>=90 Specified index of 1-8: >=80
Visual effects: C or better: B or better >= 0.75
5% -10% of the brightness level (extends in each direction should be neutral gray, and extends outward 50mm)
Practical evaluation of printed products (P2)
D50 standard light source (0.005)
500+-125 lx
Conventional index:>=90 Specified index of 1-8: >=80
Visual effects: C or better: Ideal for B or better UV: >=0.75
Transmissive film projection observation (T2)
D50 standard light source (0.005)
1270+-320 cd/m^2
Conventional index:>=90 Specified index of 1-8: >=80
Visual effects: C or better: Ideal for B or better >= 0.75
Brightness level is 5% -10% (neutral gray and extends 50mm in all directions)
Chromaticity of color display D65 light source (0.025)
75 cd/m^2 (ideally >100 cd/m^2)
_____
_____
_____
Neutral gray, dark gray or black (3)
In this standard, the basic observational lighting is recommended as the CIE D50 standard light source. In fact, the lighting is specified as the spectral distribution of the correlated color temperature at 5000K. It is said that one of the reasons for using D50 initially was that his energy distribution in the blue, green, and red bands of the spectrum was nearly equal. Manufacturers of light sources have tried their best to use a variety of materials for fluorescent lamps and color filters to obtain light sources with D50 effects. However, it is the illuminant effect of focusing and not having a lamp that perfectly matches the CIE standard illumination body D50. Therefore, the corresponding parameters are recommended in the standard to compare the actual observation light source with the theoretical light source.
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 illuminance standards are recommended in the new brightness standard, high illumination (P1) 2000+-500 lx for use in evaluating and comparing images; low illumination (P2) 500+-25 lx for simulating similarity and final viewing conditions The image tone 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 final observed quality, it is best to use typical normal viewing lighting conditions. Simulate normal viewing conditions to ensure that the dark details of the image can be resolved. The P2 condition meets 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, it is necessary to specify an observation condition suitable for high brightness (2000 lx) and suitable for low illumination.