1. Introduction
1. Research motivation and purpose
The quality control of traditional printing has been developed to a very mature stage, whether it is SWOP (Specifications for Web Offset Publication), SNAP (Specifications for Newspaper Advertising Production) or GRACoL (General Requirements for Applications in Commercial Offset Lithography). Some specifications are for reference in the control of printed output. The development of versionless digital printing in recent years can be said to be extremely rapid, but the quality control standards for its output are not yet at a mature stage. This study will use the "ISO / IEC l3660 standard for measuring the quality and attributes of output images" as the basis for experimental design, and select the two standards Graininess and Mottle for empirical discussion.
2. Research process
3. Research Framework
4. Research scope and limitations
â‘ "ISO / IEC l3660 for output image quality and attribute measurement standards" has many inspection items, which are limited by the lack of experimental equipment. In this study, only Graininess and Mottle are selected for discussion.
â‘¡Because there are many kinds of Paper materials, two papers with obvious surface differences are selected in this study: Type A mold paper and Type B glossy photo paper as the output media.
Second, the quality assessment items of ISO13660
1. Image quality evaluation items and methods
Image quality assessment methods can be basically divided into two categories: one is objective quantitative analysis, which belongs to physical, optical or chromatic aspects, such as resolution, density, color difference, etc. When comparing physical quantities, it is based on The measured value is used as the basis for quality judgment. The other type is based on the visual perception of the human eye and is more subjective. It belongs to psychophysical quantities and is related to personal preferences.
ISO-13660 is an international standard for digital copy quality evaluation. The purpose of this standard is to define and explain the procedures and methods for measuring the quality attributes of digital prints. The quality evaluation items are shown in Table 1, which are basically divided into two major items: one is characters and lines. ) The definition and measurement procedures of quality evaluation items, the second is the definition and measurement procedures of large area quality evaluation items, and the so-called large area (Largearea) refers to the area larger than 21.2mm × 21.2mm . The main items of the text and line quality evaluation of the former include 1. Blurrihess 2. Raggedness 3. Line width (1ine width) 4. Text darkness (character) 5. Contrast 6. Fill level (fiil) 7. Extraneous marks (character field) outside the text area 8. Background haze (character field) between the background and the text. The major areas of quality assessment include 1. Darkness (large area) 2. Background haze 3. Graininess 4. Mottle 5. Background excess The stains (extraneous marks. Background) 6. voids (voids).
3. Research Design
1. Experimental process
â‘ Type A and Type B paper are used to output the test guide, and the concentration value of 576 cells on the test guide is measured by a spectrometer.
â‘¡The 576 blocks take 36 cells as a unit, a total of 16 units, and calculate the standard deviation and average of the concentration of each unit.
â‘¢ Find the Graininess value of 16 units of two kinds of paper ... and Mottle value ... stdev (mi) and make a comparative analysis.
â‘£Use Type B glossy photo paper as the output paper of experiment 2, and output test guide table with two different resolutions of 300idp and 600idpi respectively.
⑤Measure the density value of 576 color patches on the guide table with a spectrodensitometer.
â‘¥ Also take 36 cells as a unit, a total of 16 units, and calculate the average of the concentration of the unit.
⑦ Find the Graininess values ​​of two different resolutions as before and make a comparative analysis.
2. Description of test guide (such as attachment)
On the left side of the guide table is the test guide table provided by QEA for reference. At the upper right, 5% to 100% is the dot concentration percentage. The lower right is a square guide with a side length of 12cm × 12cm. Due to the limitation of experimental equipment, the guide can only be divided into a minimum of 0.5cm × 0.5cm with a total of 576 cells to meet the measurement of X-Rite 528 spectrodensitometer Aperture size.
3. Research tools
â‘ Test Guide
â‘¡Printer: HP PSC l210
â‘¢Measurement instrument: X-Rite 528 spectrophotometer
â‘£Drawing software: Photoshop CS
4. Analysis and discussion of experimental results
1. Comparison analysis of Mottle and Graininess of different paper types A and B
After measuring and comparing the two output papers, although the type B glossy photo paper has a larger color saturation as expected, the colors presented are also more vivid, but the experimental data in Table 2 shows that its Mottle value It reaches 0.1457, which is larger than that of Type A O.002, indicating that Type B glossy photo paper exhibits greater noise than Type A mold paper. This result shows that when smoother paper is used, its Noise will have a higher sensitivity. In addition, the Graininess of Type A and Type B are 0.0011 and 0.0038, respectively. There is no significant difference between the two papers. The analysis may be because the sampling number of 576 points is still too small, and the measurement aperture of the concentration meter is 0.5cm. The sampling unit (0.5cm × 0.5cm) cannot be further cut. If more precise and automated measurement tools are used, whether there is a significant difference is needed for further research.
2. Graininess comparison of Type B paper with different resolutions
This experiment uses two different resolutions of 300dpi and 600dpi, and uses Type B paper as the common output medium for comparison and discussion of Graininess. As shown in Table 3, the experiment found that the higher the resolution of 600 dpi, the lower the Graininess value (0.0020), indicating that the graininess is less obvious, and it is expected to have a better output effect when outputting in a large area.
V. Conclusions and recommendations
Based on the above analysis and discussion, the conclusions and recommendations of this study are as follows:
1. Conclusion
①Graininess (moisture) and mottle (mottle) are the key items of digital printing for large-area quality evaluation to evaluate the uniformity of image density. The lower the value, the smaller the noise, and the higher the noise. Good uniformity. The type B glossy paper in this study has larger values ​​of mottle and graininess, which means that it exhibits higher noise. This may indicate that the higher the smoothness, the more susceptible the paper is to interference from printers. The influence of variables, as to what kind of interference variables are affected, needs further study.
â‘¡ Although resolution is not the only determinant of quality spoiling, in this study, higher resolution presents smaller graininess than lower resolution, indicating that it has less noise. In terms of this attribute, Higher resolution can have better quality.
â‘¢If you want to make a more accurate digital copy output quality assessment based on ISO 13660, basically it should include three main items: 1. image capture device (image capture device) 2. analysis evaluation software (evaluation software) 3. Quality standards and sampling plan. The number of samples in the sampling plan of this study can not be increased because of the equipment, which may cause a large experimental validity and standard deviation. However, this study provides a digital printing quality evaluation model, which can be used as a future digital printing quality evaluation and selection output Paper reference.
â‘£The quality assessment based on IS0 13660 is still based on objective quantification, but the observer's subjective preference of the image (preference) can not be ignored. The former can be viewed as a micro view image quality assessment, while the latter is a macro view image quality assessment, the two should still complement each other.
2. Suggestions for follow-up research
There are many test items for digital prints, which are also different from the traditional print test items. This research hopes to have the effect of introducing bricks and jade. The following opinions are provided for reference in subsequent research.
â‘ This study uses only two different paper materials as the research target, and uses smoothness as the difference comparison. It is recommended to increase the type and difference of paper materials for a more extensive discussion.
â‘¡It is recommended to increase the number of measured samples within the scope of equipment permission.
â‘¢This experiment only discusses the phenomenon of mottle with 300dpi and 600dpi. It should be possible to increase the output of more resolutions and expand the discussion of the influence of resolution on the mottle.
â‘£Whether there are differences between Graininess and Mottle in different colors, it is worth further discussion.
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