Evaluation of print quality

The wide variety of prints and their wide variety of uses make it difficult to define print quality in a rigorous manner. Most researchers believe that it is appropriate to define the quality of printed matter as "the comprehensive effect of various appearance characteristics of printed matter." What methods are used to judge the quality of printed matter and to determine the quality characteristics that govern the comprehensive effects of various appearances of printing are of great significance for improving the printing technology.

First, the quality characteristics of the overall effect of controlling printed matter

There are many researchers who have published various opinions on the quality characteristics that govern the comprehensive effect of printed materials. It is expected that these quality characteristics will be measured by instruments and finally expressed as numerical values.

P.Flik divides the printed matter into two categories: dot-printing, text, lines, and print. The quality characteristics of the dot-printing products proposed are: 1 tone reproducibility; 2 uniformity; 3 network loyalty. The quality characteristics of text, lines, and field prints are: 1 contrast; 2 uniformity; 3 faithfulness.

In addition to the above main features, the characteristics that have an impact on print quality include gloss, print penetration, overprinting, and dirt on the back.

R. Buchdahl believes that the quality characteristics that dot-printing should evaluate are: 1 Tonal reproducibility; 2 Uniformity (ie to prevent drastic changes). The quality characteristics that should be evaluated in field prints should be: 1 contrast; 2 uniformity; 3 gloss.

J.G.W. Jorgensen proposed the following main features to determine the quality of printed products: 1 Sharpness (clarity); 2 Tonal reproducibility; 3 Color reproducibility; 3 Inhomogeneity.

The above-mentioned several researchers have put forward a certain representativeness of the print quality characteristics.

The tone of the image print is transmitted through the dot. Therefore, the dot print actually refers to the image print. Its quality characteristics are more complex and typical than those of text, lines, and field prints. Therefore, most of today's research focuses on the quality characteristics of image prints. This chapter also focuses on the quality of image prints.

At present, it is generally believed that the quality characteristics of image prints take into account the following four points: 1 tone reproducibility; 2 color reproducibility; 3 image clarity; 4 print inhomogeneity.

These quality characteristics do not affect the quality of image prints independently, but interfere with each other. When the reproducibility of tone changes, the reproducibility of colors also changes. Even if the image is reproduced in the same tone, when the sharpness changes, the tone changes as the image quality changes.

Second, the method of evaluating print quality

Judging the quality of printed matter is generally based on the use of the printed matter and the visual effects that the printed matter causes people to evaluate.

Different uses of prints, their quality requirements are not the same. For example, trademarks, product samples, etc., in order to attract the attention of consumers, gloss is a must have features. In newspapers, books, and other printed materials, the gloss makes people's eyes tired, the reading efficiency drops, and the luster becomes an unwanted characteristic.

Advertisements, posters, calendars, etc. have certain ornamental value. Most of these prints are based on the representation of the subject matter of the image to determine the quality of the print. For example, in the theme-based printing, the skin color of the face is slightly deviated, and it will become a defective product. The background color is quite different, but it does not matter in assessing the printing quality. Even with the same printed matter, because the observer's main area of ​​interest (ie, the focus of attention) of the image is different, the conclusion of quality assessment is difficult to unify.

It is generally believed that the quality of printed matter is the combined result of various factors related to the quality of printing, various materials, various technologies, and quality evaluation personnel. However, due to the different living conditions and cultural accomplishments of the evaluators, the quality of the printed media is not the same, which results in a certain difference in the evaluation results of the print quality.

The method of evaluating printed materials includes subjective, objective and comprehensive evaluation.

1. Subjective evaluation of printed matter. The subjective evaluation is based on the manuscript of the copy, and the proof is evaluated against the evaluator's psychological feelings. The result of the evaluation varies greatly depending on the identity, gender, and taste of the evaluator. Therefore, at the time of evaluation, it is necessary to evaluate the quality characteristics of the printed matter in terms of the individual's identity and divide it into groups to evaluate the quality of printed matter. Therefore, the subjective evaluation method is often dominated by the psychological status of the evaluator. The evaluation result may be uniform for the quality of a certain part of the printed matter, but it is difficult to obtain a unified opinion on the overall quality of the comprehensive product. The reason is that the subjective evaluation cannot objectively reflect the quality characteristics of the printed matter. Factors that influence subjective evaluation include lighting conditions, observation conditions and environment, and back-light color. For example, the same print, viewed under different background colors, gives people different feelings, and the addition of color factors is even more complicated. Therefore, the printed matter should be observed under the following recommended conditions so that the subjective evaluation can yield better results.

1 lighting conditions. The light source used to observe the prints should produce a uniform diffuse light illumination on the viewing surface, with an illuminance range of 500 to 1500 lx, depending on the lightness of the print being viewed. Observed surface illumination should not be abrupt, and the uniformity of illumination should not be less than 80%.

2 observation conditions. When observing the printed matter, the light source is perpendicular to the surface of the printed matter. Observe that the right angle forms an angle of 45° with the surface normal of the print (0/45 illumination observation conditions), as shown in Figure 9-1(a). As an alternative observation condition, it is also possible to illuminate with a light source at an angle of 45[deg.] to the normal of the print surface, and to observe the surface of the vertical print (45/0 illumination observation condition), as shown in FIG. 9-1(b).

3 Ambient and background colors. The ambient color surrounding the observation plane should be neutral gray (N6/~N8/) with a Munsell brightness value of 6-8. The smaller the chroma value, the better, and generally should be less than 0.3 of the Munsell chroma value. Observe the background of the print should be dull Munsell color N5 / ~ N7 /, the color value is generally less than 0.3, for high color matching and other occasions, the color value should be less than 0.2.

The subjective assessment of print quality depends mainly on visual inspection. The tools used are mainly magnifiers (magnification of 10 to 25 times).

2. Objective evaluation of printed matter. The objective evaluation is to use certain detection methods to test the quality characteristics of the printed matter and use numerical values.

3. Comprehensive evaluation of printed matter. The comprehensive evaluation is based on the objectively evaluated values ​​and is compared with various factors of subjective evaluation to obtain a common evaluation standard. At present, it is necessary to further study the need to comprehensively confirm these test values ​​so as to become a standard for controlling print quality.

The evaluation of printed materials is subject to many subjective and objective factors. It is not easy to really judge quality. At present, the commonly used method is to consider the factors that affect print quality, such as reflection density, inhomogeneity, and clarity, as an index consideration, and to obtain specific values ​​through test instruments and standard materials, namely, so-called printing. Adaptability index method.

In addition, you can also use mathematical statistics methods to rank the prints to be evaluated in a subjective and objective order, and finally take the relevant numbers as the index of the best printed matter to assess the printed matter.

Reproduced from: Wins