Empirical Research on Quality Control of Digital Inkjet Output——Discussion on Graininess, Mottle
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First. Introduction
1. Research motivation and purpose
The quality control of traditional printing has evolved 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 control reference of the printed output. The development of non-print digital printing in recent years can be said to be extremely fast, but the quality control standard of its output is still not really mature. This study will use "ISO/IEC l3660 for output image quality and attribute measurement standards" as the basis for experimental design, and select the two criteria of Graininess and Mottle for empirical discussion.
2. Research process
3. Research structure
4. Research scope and restrictions
4.1 "ISO/IEC l3660 for the quality and attribute measurement of output images" has many requirements for testing. Due to the lack of experimental equipment, this study only chose Graininess and Mottle for discussion.
4.2 Due to the variety of paper materials, the papers with two different surface differences were selected: Type A mold paper and Type B glossy photo paper as the output medium.
Second, ISO13660 quality assessment requirements
1. Image quality evaluation items and methods
Image quality assessment methods can be basically divided into two categories: one is objective quantitative analysis, and the comparison is physical, optical or chromatic, such as resolution, concentration, chromatic aberration, etc. When comparing physical quantities, The measured value is used as the basis for quality judgment. The other is based on the visual perception of the human eye. The comparison is subjective and belongs to the psychophysical quantity and is related to the individual's preference.
ISO-13660 is an international standard for digital copy quality assessment. 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. They are basically divided into two major items: one is text and line (Character and Line) The definition and measurement procedure of the quality assessment items, the second is the definition and measurement procedure of the quality assessment of the large area, and the so-called large area (Largearea) refers to the area of the area larger than 21.2mm × 21.2mm. . The text and line quality assessment requirements of the former include 1. blurrihess 2. raggedness 3. line width (1ine width) 4. text darkness (character) 5. contrast (contrast) 6. Filling degree (fiil) 7. Extraneous marks (character field) 8. Background haze (character field). The large-area quality assessment items include 1. large darkness (large area) 2. background haze 3. graininess 4. mottle 5. background Stain (extraneous marks.background) 6. voids (voids).
Third, research design
1. Experimental procedure
1.1 The test guides are outputted in Type A and Type B papers respectively, and the concentration values of 576 cells on the test guide are measured by a spectroscopic concentration meter.
1.2 576 blocks with 36 cells as a unit, a total of 16 units, calculate the standard deviation and average of each unit concentration.
1.3 Find the Graininess value of l6 units of the two papers... and compare the Mottle value...stdev(mi).
1.4 Type B glossy photographic paper is used as the output paper of Experiment 2, and the test guides are output at two different resolutions of 300 idp and 600 idpi, respectively.
1.5 Measure the concentration values of 576 color patches on the guide by a spectrophotometer.
1.6 Similarly, 36 cells are used as a unit for a total of 16 units, and the average of the unit concentrations is calculated.
1.7 Find the Graininess values of two different resolutions before and compare them.
2. Test guide (such as attachment) description
The left side of the guide is the test guide provided by QEA for reference. The upper right is 5% to 100% of the dot concentration percentage. At the bottom right is a square guide with a side length of 12cm × 12cm. Due to the limitations of the experimental equipment, the guide can be divided into only 576 cells with a side length of 0.5cm × 0.5cm to meet the X-Rite 528 spectrometer. The size of the aperture.
3. Research tools
3.1 test guide
3.2 printer: HP PSC l210
3.3 measuring instrument: X-Rite 528 spectrophotometer
3.4 drawing software: Photoshop CS
Fourth, the analysis and discussion of experimental results
1. Comparative analysis of Mottle and Graininess of different paper types Type A and Type B
After measuring and comparing the two output papers, the Type B glossy photographic paper has a larger color saturation as expected, and the color presented is more vivid. However, the experimental data of Table 2 shows that the Mottle value Up to 0.1457, which is larger than Type A's O.002, indicating that the type B glossy photographic paper presents a greater noise than the Type A mold. This result indicates that when using smoother paper, the pair Noise has 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 types of paper. The reason for the analysis may be that the number of samples of 576 points is still too small, and the measurement aperture of the concentration meter is 0.5 cm. The sampling unit (0.5 cm × 0.5 cm) cannot be further cut. If a more elaborate automated measuring tool is used, whether there is a significant difference, this is for further study.
2. Comparison of Graininess of Type B Paper with Different Resolutions
This experiment is based on two different resolutions of 300dpi and 600dpi, and uses Type B paper as the common output medium for the comparison of Graininess. As shown in Table 3, the experiment found that the higher resolution of 600 dpi, the lower Graininess value (0.0020), indicating that the granularity is less obvious, it is expected to have a better output effect in large-area output.
V. Conclusions and recommendations
Based on the above analysis and discussion, the conclusions of this study are proposed as follows:
1. Conclusion
1.1Graininess and mottle are the main points of quality evaluation for digital printing for large-scale printing to evaluate the uniformity of image density. The lower the value, the smaller the noise, which means that there is a comparison. Good parity. The type B glossy photographic paper of this study has a larger value of mottle and graininess, which means higher noise. This may indicate that the higher the smoothness of the paper, the easier it is to be interfered by the printer. The influence of variables, as to what kind of interference variables are affected, is for further study.
1.2 resolution is the only determinant of quality spoilage. In this study, higher resolution shows less graininess than low resolution, indicating that it has less noise. For this attribute, Higher resolutions have better quality.
1.3 To make a more accurate digital copy output quality evaluation based on ISO 13660, basically three items should be included: 1. Image capture device 2. Analysis software 3. Quality standards and sampling plan. The number of samples in the sampling plan of this study cannot be increased, which may result in greater experimental validity and standard deviation. However, this study provides a quality evaluation model for digital printing, which can be used as a future digital quality evaluation and selection output. Reference for paper.
1.4 The quality assessment based on IS0 13660 is still based on objective quantification. Only the observer's subjective preference for images can not be ignored. The former can be regarded as the image quality evaluation of the micro view, while the latter is the image quality evaluation of the macro view, and the two should still complement each other.
2. Suggestions for follow-up studies
There are many testing items for digital prints, which are different from the traditional printing test items. This study hopes to have the effect of throwing bricks and jade, and provides the following opinions for reference.
2.1 In this study, only two different paper materials were used as the research target, and the smoothness was used as the difference comparison. It is suggested that the paper types and differences can be increased for more extensive discussion.
2.2 It is recommended to increase the number of samples measured within the scope of the equipment license.
2.3 This experiment only discusses the mottle phenomenon at 300dpi and 600dpi. It should increase the resolution output and expand the influence of resolution on the mottle.
2.4 Whether the different colors are different between Graininess and Mottle is worthy of further discussion.