Standardization of soft proofing

First of all, there are "environmental conditions for soft proofing of the screen" in international standards. This is the standard established in the 1990s. In our country's industry applications, there are many defects in the soft proofing of the screen. The main defect is the display problem of the screen itself. The structural lighting principle of the fluorescent screen itself cannot be used as a basis for customers to sign, but this is a trend. .

Then I first introduce the relevant content of this standard.

Display the required environmental conditions:

Ambient light should be neutral. For example, the colors of curtains, walls, and the color of the operator's clothes may affect the screen. The background light requirement is that the light diffusely reflected by diffused glass is most suitable. Our regular fluorescent tube is not strictly diffuse, it requires a diffusion plate.

The illumination of the environment should be moderate. Illumination is not as bright as possible. The illuminance of the environment is too bright will affect the display effect. Therefore, the international standard requires that the monitor must be equipped with a hood, which is to reduce the light around the interference to a small extent. After adding the hood, the color is completely different, the contrast is improved, and the color is also pure. This is because the interference light source is reduced.

The second standard related to our monitors is what China has now. We referenced the European standards for standard light sources in the early 1990s and related standards in the United States and developed an industry standard called “color evaluation”. This is the CY/T3 industry standard. This is an industry standard that has been transformed from an international standard. This standard involves four requirements:

The first aspect: color temperature

The color temperature is the most important condition of the standard light source. The national standard was the D65 light source used at that time. The color temperature was the absolute temperature 6500K, K is the absolute temperature, and it was 273.12 degrees Celsius temperature difference. According to the information we received in October, The new international standard is now being revised. It has a technical report in which the D50 light source is recommended as a new international standard, but the original D65 standard also serves as a reference standard. Now Roland and Heidelberg are already D50 light sources. The feature of this light source is that the D50 should be warmer than the D65. Our human eyes will not feel too comfortable to see colored originals and printed materials under the light source of the D65, which is the white point. The D50 is a bit more comfortable. We prefer the D50 light source to the color temperature. We have not changed this standard because the official text of the international standard has not yet come. Now both of these light sources can be used in a coexistence state.

The second aspect: color rendering coefficient

To be greater than 90%, which is equivalent to its spectral composition similarity under natural light conditions, then the real natural light refers to sunny morning 9:30-11:00, 2:00-3:30, not daylight In the case of direct radiation, it is completely reflected by the sky. This kind of natural light, natural light, is difficult to simulate. After we have collected and analyzed the natural light's spectral components, our standard light source will simulate natural light conditions. The degree of simulation is expressed by a color rendering coefficient, which is found in many reference books because the color rendering coefficient of our ordinary fluorescent lamp is still relatively high, and the general color rendering coefficient can reach 93%. The fluorescent lamps, such as Panasonic's, it's up to 95%.

The third aspect: illumination

They are now doing a lot of art reproduction, so the illumination of his light source has become a very important condition, although our standard light source uses 1000Lux, plus or minus 500 Lux, and the US standard is 1500, plus or minus 500, Its central value is 1500, and we are 1000. This is when we set the standard when we consider that our country's energy is relatively tight, so we set the standard lower. So what is the concept of 1000, is the four 36W Philips fluorescent lamps, its color temperature is closer to the D65 light source, the lamp and lamp spacing is 10 cm, the lighting distance is about 1 meter 2 and we can use a luminaire to four The fluorescent lamp shades together, so it is better to use a waste PS plate to turn it into a reflection lamp. Under such conditions, we use the illuminometer to measure about 1000 Lux. The illuminance is directly related to the distance from the light source. The closer the illuminance is, the greater the illuminance is, the farther it is, the smaller the illuminance is, so the illuminance is not only the luminous power of the lamp. It is related to the luminous coefficient and has a direct relationship with its distance.

The fourth aspect: observation conditions

The angle of incidence (angle between the beam and the normal) is "0 degrees", the angle of reflection is "45 degrees", or the angle of incidence is "45 degrees", and the angle of reflection is "0 degrees." We have recently done high-fidelity experiments in companies, and rainbow copying works of art all have this problem. If we observe an inconsistent angle, the color of the same print or digital proof will appear to be inconsistent with the color you are chasing, or close to it. The degree is not the same. This is what we call metamerism or isospectral heterogeneity. Both of these possibilities may exist. In addition, some of our prints are glazing, some are not glazing, some have good gloss after printing, and some inks are more dirty, which will affect our visual judgment. So we found that many international standards include the determination of the Pantone color standard, the determination of the 23 basic colors in the international standard, and the tristimulus value XYZ that our colorimeters use to simulate human eyes. These are the simulated human eyes. The acquisition of these simulation data and the simulation curve are simulated by the visual effects of a large number of experienced people. The main simulation is the human eye. Therefore, the Lab color space can be done regardless of the device. The densitometers like ours are firstly associated with color filters. The density values ​​obtained by different filters are very different. But there are still a few differences between the few brands of densitometers or chroma timings, such as Glinda, X-Rite, and Germany's Contac, but the difference is already small. Therefore, the observation environment, the observation angle, whether it is specular reflection or diffuse reflection, will bring many problems to the observation print. For example, we are now using laser digital proofing, there are two kinds of toner used, one containing a very high silicone oil, very bright after finish curing, a little containing silicone oil, looks closer to the effect of printing ink, so The effect of heat curing after the two toners is also different, which leads to a difference in color judgment.

Another standard is the standard of the file format. At present, the national standard is still being worked out. Now the TIFF format is used. Although there are many branches of the TIFF format, the TIFF format introduced from the international standard is relatively complete. Now we are working on the PDF standard. Because of the large number of applications of the Internet, the need for long-distance transmission requires the use of the PDF format. The original PS format used by PageMaker has not become an international standard, but has become an industry standard. Mature PDFX1, X2, X3, we are also developing the corresponding national standards.

Then the ICC document is actually the document format of the International Color Consortium. The judgment of the color of his document format also uses the method of chromaticity value, so there is no standard in itself, because the chromaticity value and the chromaticity space have become international standards. . There are many ways to describe color, such as CMYK to describe it, and chromaticity space to describe it. Of course, the benefits of color space are not related to the device. Of course, it is still described in RGB, and it has become popular, and the suggestion file is being Before RIP processing, all are described by RGB, because the description of CMYK is nonlinear to the judgment of the eye, and the depth of the color represented by the percentage of dots is exponentially related to the observation of the human eye, or conversely, the judgment of human eyes on color. It is a logarithmic relationship. At this point, RGB and the human eye are closer to the judgment of the color, and its greatest advantage is that it is perfectly matched with the computer bus, because RGB is represented by gray scale, so in terms of industrial processing of image files, Many aspects have been expressed using RGB. The benefits of RGB are many. For example, if the scanned file is already in RGB format, it needs to be corrected and then converted to CMYK. Now digital cameras directly record RGB files. Plus, the monitors we use today are also RGB files. There are many proofing systems that can directly output them. The source files used by high-fidelity technology in the world are also RGB, so the RGB format is likely to become the mainstream of future image colors. And now the JPF format from CIP3 to CIP4 not only controls graphic and text information, but also control information and management information. Such a file has an advantage and will become an international standard. Once it becomes an international standard, we will bring it back to us. International standards.



Source: Ke Yin Network

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