Same color difference preview
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
Customer complaints
"Our products are printed by myself personally. Every edition is the first one that I confirm the color and signed the 'OK'. The color that I confirmed on the shop floor is very high, the color effect is also very good, I am also very Satisfied, but now the color of the product I received and the color of the digital sample are far from each other. What is going on here? How do you manage quality?"
Similar complaints from customers like this, I believe that many printing companies have received it, and customers have never even returned. In fact, this is not the printing master did not match the good color, not the process quality control is not good, "metachromatic" is the culprit.
problem analysis
When shopping in a mall in real life, you feel like the color of a certain product, hat, etc. under the fluorescent light, but the color seen under the incandescent lamp is not the same when you buy it home. If you are a printing buyer, the color of the printed products confirmed by the printing company at the time of printing will be observed in your own office environment, and the color perception of the printed matter may be biased.
The formation of color is inseparable from the spectrum, and any object has a specific spectral reflectance curve. When the spectral tristimulus values of two objects of different spectral reflectance curves are equal, the two colors are considered to be conditionally equal colors. Since the energy distribution of each light source is different, once the light source changes, the generated spectral tristimulus values are no longer equal, and the color results are also different.
The generation of color sensation requires four major elements: light source, color object, eye and brain. Any one element is uncertain or changes during observation. The color result of feedback will change, and the observer can not accurately judge the final color effect. Therefore, in reality, factors affecting the color evaluation result in addition to the observer itself, as well as the light source, the size of the object, the angle of the observer, and the background color of the target observation object, etc. Table 1 visually shows the color results of these factors. Impact.
The reproduction of a color has a certain relationship with the characteristics of the light source for observing the color. Two objects present the same color under one light source, but under another light source, they have different colors. This phenomenon is called "same color". The phenomenon of heterogeneity. In fact, the process of color printing reproduction is to use the phenomenon of metamerism to achieve the purpose of reproducing color. However, the result of color matching is extremely easy to break in the case where the coloring conditions change. The color matching of the printing process often only achieves the homochromatic matching under a certain lighting condition.
Color and density measurements are a common method of controlling the quality of an item's reproduction in printing. In the printing process, we usually compare the copied image with the original image to determine the degree of color reduction, so as to obtain the faithfulness of the original image. Although we try to take quantitative indicators to avoid the influence of human factors on the degree of image reduction, the observation of human eyes still plays an important role in image restoration, so it is obvious that the error in color observation in the printing field is controlled. Especially necessary.
Because the light source and observation conditions are different, there are also differences in the color development of each material (such as paper and ink), which directly affects people's judgment on the final effect of the printed matter. To avoid misunderstanding of the color reproduction effect, ensure the reproduction and final observation of the printed matter. There is a uniform observation condition in the link. The ISO 3664 standard has strict regulations on the color evaluation of the printing industry, as shown in Table 2. The following is a brief introduction to some of the indicators in the regulations.
The color of a light source, called the color temperature, is expressed in terms of the absolute temperature Kelvin (K) by the different colored lights emitted by the black body to different temperatures. The color temperature of the light source determines the color characteristics of the light source. The color temperature of the light source depends on the relative energy ratio of light of different wavelengths in the light emitted by the light source. The higher the K value, the more the color appears to be white-blue; the lower the K value The color of the appearing tends to be yellowish red.
The illuminance is the intensity of the light. The higher the illuminance, the brighter the light source; the lower the illuminance, the darker the light source. For printing applications, there are two main use cases. One is to use high-illuminance light source illumination, so that you can find every detail of the print, which is used when strictly comparing the prints, but for the highlights of the highlights. The effect is greater and may result in loss; the other case is the use of relatively appropriate illumination as a daily inspection of the printed matter.
The color rendering index Ra is a measure of the ratio between the color that can be seen by a certain light source and the color that can be seen under natural light. The closer Ra is to 100%, the smaller the difference between the color developed and the color developed under natural light illumination. For the printing industry, the higher the color rendering index, the higher the degree of reduction in color observed therein; the lower the color rendering index, the lower the degree of color reduction. Generally, Ra ≥ 90%.
The metamerism index (ultraviolet light region) is less than 1.5, preferably less than 1.0. Paper mills add fluorescent whitening agents to the paper in order to increase the whiteness of the paper. The UV spectrum in the light source will excite the fluorescent component in the paper, causing errors in the resulting color results. The higher the UV spectrum content, the greater the color difference.
Solution suggestion
First of all, whether it is printing production or the final color visual evaluation of printed matter, it must be carried out under a uniform light source that conforms to the ISO 3664 standard. Otherwise, metamerism will occur, eventually leading to visual differences in visual perception. The D50 standard light source is the first choice for color visual evaluation.
Secondly, when the customer wants to visually evaluate the color and there is no standard light source available, if the weather is good, the customer may be advised to take the sample to the outdoor natural light for visual evaluation of the color, so that the color error will be reduced a lot, but keep in mind It is necessary to remember that the color visual evaluation should not be carried out in the morning or evening time, and that the sunlight is not directly reflected on the target evaluation sample.
Finally, since there are scientific methods, there are unscientific methods, and sometimes unconventional methods can help us solve or cope with immediate problems. In reality, it is inevitable that you will encounter customers who are smashing, so that you can't reverse their thinking, insist on visual evaluation of colors according to their own non-standard light source conditions, and customers are core customers, and can't afford to offend, what should I do? It is a temporary measure to meet the customer's requirements by temporarily installing the same type of light source as the printing process on the printing machine's sample platform. However, companies still must constantly implement standard methods for customers to train and guide customers to manage and evaluate colors in the right way. It must not make "non-standard" become "standard."
Of course, the best way to color evaluate is to use a standard instrument for data measurements. The instrument is not affected by the mood, and there is no judgment difference caused by human sensory differences. It is the most scientific and objective color evaluation method.
The phenomenon of "metachromatic" is one of the principles of printing technology. It is a double-edged sword. On the one hand, it enables the reproduction of printing colors, and on the other hand, it brings limitations to the color evaluation of replicas. Light source conditions for color reproduction and evaluation. In the color management process, the standard light source plays a vital role, and it is the most easily overlooked. Whether it's a printing company or a print buyer, it's important to remember that a standard must be based on one or more standards.