Введение в новые условия просмотра по стандарту ISO 3664 в печати

Color and density measurement is a common method for controlling reproduction quality in printing. But for a single image, these related test methods cannot replace the human eye's final evaluation of the color quality reproduction. In print reproduction, we mainly compare the reproduced image with various graphic originals to judge the degree of fidelity of the color reproduction. For example, to evaluate the color quality of a reproduced color image, a commonly used method is to reach a conclusion about the fidelity of these images to an original image and to the original.

Undoubtedly, the best viewing conditions for controlling print reproduction during the printing process should match the final viewing environment of the printed product. If the final viewing environment is very clear, printing staff can monitor the quality of the printed product under the same conditions. But this situation is generally unlikely, and more importantly, the final viewing conditions do not allow us to make a direct comparison between the original, the photo or the contract proof and the final printed piece. This is because under the light source and the related viewing conditions, the way each material renders color directly affects the final image effect. Their appearance is often different. To avoid misunderstanding of the color reproduction effect, it is very necessary to use stable viewing conditions during the product reproduction process.

The surrounding objects in the viewing environment, or the surfaces of the objects present there, their colors and brightness also greatly affect the observer's perception of the color of the object being viewed. For this reason, people use a standard viewing booth for observation. But an ordinary viewing station is built in some part of a room. So control of the viewing environment is very important.

To ensure uniform viewing conditions in all reproduction steps, it is imperative to recommend a unified viewing standard. For the viewing conditions of color prints and photographs, the recommended standard is

ISO3664

. The new version will be issued in

Before the new standard was issued there were already two standards,

ISO3664

Viewing Conditions for the Illumination of Color Transparencies and Reproductions》and

PH2.30-1989

Viewing Conditions for Printed Matter, Photographs, Color Prints and Projected Laser Imaging Reproductions》. They are very similar in their recommendations on viewing standards, but not entirely identical. The new

ISO3664

standard's revision began in

at the end of the year,

The association stated that the new version of the standard is

In the printing and reproduction process, to ensure stable and consistent viewing conditions, there are the following key factors:

, the spectral energy distribution of the illumination source

, the luminous intensity and uniformity of the illumination source

, the viewing environment conditions (including both the viewing environment and the illumination environment)

, the stability of the illumination environment

ISO3664

The new version includes all the required recommended standards. At the same time, the new version of the standard also makes recommendations for image viewing on color screens and for the conditions of picture exhibition and appreciation. This standard will also apply to the printing and photographic industries.

ISO3664

the key clauses in the viewing standard are introduced.

) This parameter recommendation specifies the light energy distribution of the light source for reference illumination other than color displays; for color displays, the color rendering tolerance of the white point is indicated in parentheses. These descriptions are all obtained from

visual observation by the system.

) When comparing a transparency with a printed piece, the ratio of the illuminance of the transparency's light source to the illuminance of the equivalent printed viewing plane is

) The ambient illumination of color displays should be less than or equal to

=64 lx

may all be used.

In this standard, the basic viewing illumination is recommended as

CIE D50

standard light source; in practice, the illumination is specified as having a correlated color temperature of

in daylight spectral distribution. It is said that one reason for initially using

is that its energy distribution in the blue, green and red bands of the spectrum is close to an equal-energy state. Light source manufacturers have tried every means to use various materials to make fluorescent lamps and color filters in order to obtain

light sources with that effect. However, in fact no lamp's light output matches

it completely. Therefore, corresponding parameters are recommended in the standard to compare the degree of matching between real viewing light sources and theoretical light sources.

the specified viewing conditions in

Reference illumination and color difference

CIE13.2

Metamerism index

CIE51)

(min:max)

Reflectance of ambient illumination

Conditions for the appraisal and comparison of printed matter

(0.005)

2000 lx -500 lx (

-250 lx)

the specified index is

or better UV:<4

>=0.75

should be neutral gray and non-reflective

Transparency direct viewing

(0.005)

1270 -320 cd/m^2 (

160cd/m^2)(2)

the specified index is

>=0.75

5%-10%

extending in all directions should be neutral gray

Practical appraisal of printed matter

(0.005)

500 -125 lx

the specified index is

>=0.75

ideally neutral gray and non-reflective

Projected viewing of transparencies

(0.005)

1270 -320 cd/m^2

the specified index is

>=0.75

5%-10% (

neutral gray and extending in all directions

(0.025)

75 cd/m^2 (

>100cd/m^2)

neutral gray, dark gray or black (

In this standard, the basic viewing illumination is recommended as

CIE D50

standard light source; in practice, the illumination is specified as having a correlated color temperature of

in daylight spectral distribution. It is said that one reason for initially using

is that its energy distribution in the blue, green and red bands of the spectrum is close to an equal-energy state. Light source manufacturers have tried every means to use various materials to make fluorescent lamps and color filters in order to obtain

light sources with that effect. However, in fact no lamp's light output matches

it completely. Therefore, corresponding parameters are recommended in the standard to compare the degree of matching between real viewing light sources and theoretical light sources.

In earlier standards, the degree of matching was specified using

the color rendering index. It reflects the degree of similarity between the colors shown by a series of standard color patches under a theoretical

light source and the colors they display under the actual viewing light source.

If the colors we deal with have a spectral emission curve, and

the varnishing effect of the varnish will not affect it in any way, then we can use

the standard of that year without any modification.

Color imaging and proofing systems, when creating images,

use many new technologies

dye sublimation, thermal transfer, inkjet, electrostatic imaging and so on. The use of these methods is gradually increasing the color contrast of images. The primary colorants used by these technologies, mostly when matching photographic or ink-printed color effects, show abrupt changes in their reflectance curves at certain points relative to the color curves they match. This is called metameric matching. The negative effect of metameric matching is that colors are very sensitive to changes in viewing conditions. In this way, using only the color rendering index to describe the characteristics of a light source is no longer enough.

The new standard retains the characteristic of the color rendering index while adding two new standard parameters: visibility and

the color shift index. These two indices come from

1981--

methods of evaluating light source quality. These parameters use more complex matching criteria. One specifies the visibility situation, one specifies the situation of the spectral

part, so as to more strictly distinguish actual light sources from

CIE D50

ideal illumination.

That is to say, if it conforms to the new standard, viewing equipment will provide more stable viewing conditions. This will reduce problems arising from the sensitivity of new materials or fluorescent lamps to paper and ink.

Preliminary tests show that most of the viewing devices considered good under the old standard also conform to the new standard. Equipment defined by the earlier standards may have many problems

and need to be updated, so it cannot yet be used to show which recommended index is feasible, and those still require further work.

GATF/RHEM

light source indicator can warn about the viewing environment when the viewing conditions are incorrect. If this device is installed directly under working conditions to remind staff of the situation of the viewing environment, it will be very convenient. But note that

GATF/RHEM

cannot indicate the correctness of the viewing conditions.

The new standard recommends two illuminance levels: high illuminance

(P1) 2000 -500 lx,

for use when evaluating and comparing images; low illuminance

(P2) 500 -25 lx

, used for image tone viewing that simulates conditions similar to the final viewing conditions. The revisions to the earlier standard in terms of appraisal evaluation and comparison are very necessary. For example, comparing the effect of an original and a proof, or comparing subtle color differences between a contract proof and a printed image during printing, falls under this recommended standard.

Thus, although viewing conditions have a certain degree of adaptability, changes in illuminance level also have a very significant effect on how an image appears. In order to simulate the final image viewing environment, use the recommended low illuminance level

. Although the illumination conditions in everyday viewing also vary, the choice of the standard illuminance condition is the most representative illumination situation for our ordinary viewing.

In the industry, the recommendation of the low illuminance level aroused considerable controversy. It was pointed out that too many illuminance recommendations might cause confusion. Therefore, the following note was appended after the standard to explain:

Note: When "emphasizing the comparison of image detail effects," this should be carried out under illuminance higher than that of ordinary viewing, which will be favorable for observing subtle differences between images. For example: a contract proof and a printed proof can be easily compared and distinguished. Therefore, all quality comparisons of two or more images must be carried out under

these conditions. However, for the tone reproduction and true quality judgment of a single image, it is best to carry it out under conditions matching the final viewing conditions. This is consistent with the conditions under which readers view the image. However, what the final viewing conditions are like, we may not know. Without knowing the final viewing quality, it is best to use typical normal viewing illumination conditions. Simulating normal viewing conditions must ensure that the shadow detail of the image can be distinguished.

conditions meet this situation.

David McDowell

Mr. (one of the authors of this article) believes that the following practical application issues should be emphasized: "Recently, I observed the same image under several different lighting conditions. The picture content included a very delicate piece of lace, whose color was very close to the background. My viewing result under the standard viewing table was not as good as the result under the office environment. The very beautiful image seen in the office appeared pale when viewed under the viewing table, like a water-soaked effect. Some time later, I came across an advertisement picture about a large wholesale process. The picture was in color, and the content was a picture of black lawn-care workers and lawnmowers against a black background. My reaction was, how can such an image be reproduced? We could hardly see anything on it. But when I observed it again under the standard viewing table, even the shadows in the image could be distinguished without any problem. We probably encounter this situation often as well, so we might as well try to pay attention to it."

Besides viewing the match between the reproduced image and the original on the viewing table, we can also observe the image in a hall, an office or other low-illuminance place. Such changes in lighting conditions, whether in brightness level or in color characteristics, cannot be controlled. If we use this varying illumination for proofing, especially when using certain new materials, we will be forced to adjust the color effect of the image. Therefore, stipulating a low-illuminance viewing condition suitable both for high-brightness viewing conditions (

2000 lx

) and for low-illuminance viewing conditions will be a very advantageous thing. In this way, the tone reproduction effect of the image can be judged more truthfully. More importantly, we can simulate this viewing condition in other places, thereby obtaining the same viewing effect.

The standard also specifies viewing standards for transparencies and projected images. For direct viewing, the central illuminance of the transparency illumination should be

1270cd/m^2 -cd/m^2

, and it specifies that the surrounding environment should, at least in an area of the width away from each edge of

present a neutral gray state, with illuminance not exceeding that of the image viewing surface

. If a transparency is mounted with an opaque border, there is no need to remove the border.

During viewing, the surrounding conditions also play a very large role in affecting the viewing effect. In the new standard, the following conditions are noted:

, the viewing environment should minimize interference with image viewing. In order to avoid other conditions affecting the judgment of a transparency or printed piece, after entering the viewing environment, one should avoid immediately starting the evaluation work. The human eye needs at least a few minutes to adapt to the environment.

, extra light, whether emitted from other light sources or reflected from other object surfaces, will have an effect on viewing or on other image illumination.

, in the viewing environment at that time, there should be no strongly colored surfaces (including clothing).

Note: Strong colors in the viewing area are a potential problem, because they may produce unavoidable reflections. Reflections from the ceiling, walls, floor or other surfaces in the field of view may cause neutral gray patches with a reflectance lower than

to change color.

The new standard also points out that the neutral, non-glossy surrounding environment at the edge of the viewing range should extend beyond the viewing space on each side by at least

. The reflectance of the surrounding environment should be less than

. The new standard also points out at the same time that images to be compared should be placed side by side.

Maintaining the stability of the light source

Generally, observers do not have the corresponding test equipment to test the illuminance and spectral energy distribution on the viewing table. So the conventionally used method of maintaining the viewing environment is to replace the lamps regularly. The standard proposes that manufacturers should state the guaranteed service time of the equipment or instruments and remind users to carry out maintenance on schedule, unless users have sufficient reason to show that the equipment is in normal working condition. It suggests equipping viewing devices with corresponding operating-time test equipment or other instruments with attenuation indication. Some manufacturers use

2500-5000

hours, or one year, to state the service time of the lamp, but they do not propose that the viewing table surface should be kept clean and tidy.

Display screen viewing conditions

The industry has never recommended any conditions for viewing images on display screens. If people do not need to rely on what is shown on the screen to judge the final image effect, it will not be a problem, and we need not argue about whether the viewing method is feasible. However, to obtain stable viewing, a stable viewing condition needs to be provided. The new standard includes a description of screen viewing standards that is distinct from any form of copy. Of course, the specified viewing conditions should be effective for the simultaneous viewing of hard-copy images or screen images. Another standard

ISO12646

《Graphic technology — Standard for color proofing using a color display》is being formulated. It is by

the graphic technology association of

developed, and includes more recommended standards concerning the viewing details for direct on-screen image comparison.

ISO 3664

includes the following descriptions regarding display viewing:

, the white chromaticity on the display screen is close to

the standard; the brightness of white must be greater than

75cd/m^2

100cd/m^2

, when testing any display screen or viewing surface, the ambient illuminance should be lower than

. The color temperature of the ambient illumination must be <

the color temperature of the display's white point.

, the area surrounding the displayed image should be neutral, preferably gray or black with low flicker, with chromaticity values close to the white point of the display.

, the display needs to be placed in a viewing area without strong color reflections (including clothing), because strong colors may produce reflections on the display screen. The ideal state is that all walls, floors and furniture in the field of view should be gray or free of any posters, signs, images, text or other objects that affect the observer's vision.

, other light sources or light spots should be avoided in the environment, because they cause a reduction in the image quality effect. The display should be placed in an environment free of direct lighting fixtures, windows and other objects that produce reflections on the display screen.

For light sources whose correlated color temperature is different from

, the conditional color matching and the color rendering index of colors specified in the standard do not apply. In this state, users must understand the degree of similarity between the spectral distribution of the tungsten lamp and the theoretical perfect radiator. If the spectral distributions are very close, then the chromaticity, conditional color matching and color rendering will be very close.

ISO 3664

also includes test conditions and experimental data relating to the demonstration of the validity of the standard.

Because "in the process of judging the content of an image or exhibiting pictures, human subjective impression is a very important criterion for judgment." This standard includes an appendix, "Viewing standards for judging and exhibiting pictures."

(This standard applies to both printed matter and color photographs at the same time). Table

lists the recommended viewing conditions in this appendix.

Recommendation: Viewing conditions for judging and exhibiting pictures

Recommended viewing conditions

degree viewing angle, if a tungsten lamp is used, the correlated color temperature is

Transmitted image (direct viewing)

TI viewing conditions (diffused light)

degree viewing angle, if a tungsten lamp is used, the correlated color temperature is

, the illuminance level reaches

375 lx

Transmitted image (direct viewing)

viewing state (diffuse illumination), if a tungsten lamp is used, the correlated color temperature is

240cd/m^2

times below the hidden light spot luminance.

Note: Under typical direct viewing, the hidden light spot illuminance is approximately

0.0016

times the illuminance of stray light on the illuminated surface

Transmitted image (direct viewing)

viewing state, if a tungsten lamp is used, the correlated color temperature is

40cd/m^2

times below the hidden light spot luminance.

Note: Under typical direct viewing, the hidden light spot illuminance is approximately

times the illuminance of stray light on the projection surface

Color printing processes have yet to develop, and customers expect greater color stability and quality requirements. The printing industry is a highly fragmented process, and the reproduction of color images involves the participation of many different companies. Because of the characteristics of color perception, communication between different companies is very difficult. Therefore, the recommendation of standard viewing conditions for color observation is very important.

Visual communication of images under standard illumination conditions is a necessary process in printing. The new version

will help reduce errors during critical color processing or evaluation.

It provides and specifies complete and clear viewing conditions for the printing process. If we consciously use equipment conforming to

standard viewing equipment.

——This article is reprinted from China Packaging Network (pack.cn), original link: http://news.pack.cn/show-362245.html