There are three factors that affect the quality of printed images:

(1) Aesthetic factors Prints are visual products. When people evaluate print quality, the first impression is the aesthetic effect of prints. Font selection, color design, art patterns, image placement, layout layout, and selection of paper and ink are all related to the aesthetics of the print.
(2) Technical factors Technical factors are the factors affecting the quality of printed products in various processes of printing production. In the limited range of platemaking, printing equipment and printed materials, as far as possible faithfully reproduce the design content. The technical characteristics of print quality include image clarity, color and tone reproduction, gloss, and texture.
(3) Consistency factors The main question involved in the consistency factors is how much variation can be allowed between the printed sheets. This is a major issue in the quality stability of printing. The printing time was extended accordingly, or the printing plate was changed in the middle, or due to the failure of paper, blankets, printing presses, etc., resulting in mid-stream shutdown, which would cause the ink-water balance to be disturbed. Once the ink balance relationship changes, the print quality may be inconsistent.

Several requirements for the method of evaluation There are the following requirements for the method of evaluating the quality of printed matter:
(1) To distinguish and identify different parameters by human vision:
(2) The importance of each parameter should be estimated by each evaluator;
(3) It is necessary to convert the response of each evaluator into a common format;
(4) To estimate the response deviation of each evaluator;
(5) Maintain the potential print quality relationship between experimental samples.

Classification methods of evaluation methods The printing industry often classifies print quality evaluation methods into subjective evaluation and objective evaluation. Subjective evaluation usually refers to quality judgement by people rather than instruments. Visible, "objective" and "subjective" can be regarded as "instrumental" and "non-instrumental" synonymous. The two evaluation methods combined to form a comprehensive evaluation method.
The subjective evaluation method requires the assessors to evaluate according to their subjective impressions, in which paired comparison methods, multidimensional classification methods, scale evaluation methods, limit methods, etc. have been formed.
The objective evaluation method is essentially to quantify the image quality with the appropriate physical quantity or quality characteristic parameters, so as to provide the basis for effective control and management of the printing quality. The main contents of color image print quality evaluation include color reproduction, tone reproduction, definition and resolution, microscopic quality of the dot, and quality stability. Densitometers, spectrophotometers, control strips, and image processing methods can be used. Out these quality parameters.
The comprehensive evaluation method is to give "weighted value" to non-independent print quality parameters that have different effects on image quality. These weights can be calculated using multivariate regression analysis and fuzzy mathematics. Subjective evaluation methods can also be used for objective evaluation methods to determine variable issues that are difficult to resolve.
Quality parameter classification

1 The non-information surface of the printed image The surface of the printed matter can be divided into two parts according to its function: information surface and non-information surface.
The information surface of a printed matter contains information or images to be expressed by the printed matter, and the non-information surface usually forms a background, and the information surface is rendered against the contrast or the desired atmosphere.
The non-information side of printed matter can be divided into three types: unprinted paper (or other unprinted printing surface), solid printing surface, or uniform mesh surface. The general characteristic of a non-information surface is that the entire area has a uniform appearance.

2 The basis for judging the image goodness The fundamental goal of research quality is mainly to determine the degree of "good" sample, that is, to evaluate the "goodness" of printing quality. The basis for the evaluation is generally three cases: (1) the criteria for evaluation are ideal, and the best print is the basis for comparison; (2) the objectives to be achieved for the product are used as a basis for identification. This objective may be a proofing sample. Or the original line manuscript, then the quality of the judgment mainly from the size of the deviation; (3) aesthetics, that is, the impact of print on the viewer, this situation is mainly focused on the evaluation of printed products, not focused on Compare the originals.

3 Printed image information surface The function of printing image information surface is to convey the information to be expressed in the print, which usually contrasts with the background part. The information plane may be a line image, or it may be a monochrome halftone image and a multicolor halftone image. Both the text and the line-drawing manuscript reproduced images belong to the line image, which transmits the image information through the shape and layout of the image information face. This image usually has a high enough color intensity but no hierarchy, and it is generally expected that it contrasts with the background to form a clear contrast.

The second method of transmitting information on prints is to use a mesh density level to produce images. Mesh prints should have a good "uniform mesh" characteristic and expected density distribution in order to achieve the desired effect of the image.

The third method uses color changes to convey more information in addition to the density level. This ability is obtained by overprinting several different colors of halftone images. Satisfactory printing colors can be obtained with trichromatic inks, the purpose of using black ink is just to get better quality. The quality parameters of such prints are much more complex than the previous ones, and it also involves complex color balances and other issues.

Subjective evaluation method

1 Multidimensional scaling Multidimensional scaling is a scaling technique based on mathematical statistics. In the case of pair-wise comparison of differences between samples or determination of sample satisfaction, multidimensional scaling methods can be used to analyze and identify the main parameters used in people's assessment. When judging a printed sample in this way, the relative importance of the main parameters of the printing quality can be determined; the value obtained from the evaluation can make the subjective evaluation and the objective evaluation or intrinsically related to the nature of the paper; the quality of each print can also be obtained. The reliability of the evaluation, the consistency of each evaluation staff (such as printing, papermaking experts, readers, advertising staff, etc.) and the evaluation team's evaluation and other information.

Multidimensional scaling technology was proposed by Tokosson. Its content is: If there is a perceived difference between two elements, then the difference can be expressed in a geometric distance. If this difference is recorded on a scale, the scale on the scale shows this distance, and then the distance can be used to create more than one-dimensional geometric models that reflect the relationships between the samples.

An important feature of multidimensional scaling technology is that it can be used to multidimensionally scale the subjective psychological factors of the judges. The role of each parameter in an evaluation can be represented by a desired vector.

2 Pairs of comparisons The judges have subjective characteristics when judging the quality of printed matter. Different people will make completely different conclusions. This kind of objective inconsistency cannot be regarded as bias or randomness and ignored. Even if there is a reference that can be used as a benchmark for comparison, there will be inconsistencies in the evaluation results, and the inconsistencies in the subjective evaluation cannot be regarded as deviations and randomness, either.

In many cases, there is no reference that can be used as a benchmark. At this time, only internal comparisons can be made between the objects being evaluated. There are two commonly used methods: (1) arrange the judged samples in a certain order; (2) put a set of judged samples in each sample Samples are compared with other evaluated samples one by one, scored on the basis of comparison, and judged according to points. This is the pairwise comparison method. It belongs to a subjective evaluation method.