An investigation of print quality defects: Psychophysical evaluation of content masking, development of web-based troubleshooting tools, and analysis of sharp roller bands
The current dissertation aims to discuss three research topics within the field of print quality defect. The first topic concerns a new psychophysical experiment to investigate the visibility of fine pitch halftone banding, and the second topic introduces web-based print quality troubleshooting tools for printer users to self-solve print quality issues of their HP printers. The third topic, which constitutes the main part of this dissertation, is pertinent to assessment of the presence of isolated large pitch periodic and aperiodic bands in laser Electrophotographic printer output. In addition, to improve the robustness and efficiency, two updated methods for estimating the repetitive interval for periodic bands are discussed. Observing and evaluating print defects represents a major challenge in the area of print quality research. Visual identification and quantification of these print defects have become a key issue for improving print quality. However, the page content may confound the visual evaluation of print defects in actual printouts. To address this important issue, Chapter 1 of the present research is focused on the banding in the presence of print content in the context of commercial printing. In this chapter, a psychophysical experiment is described to evaluate the perception of the bands in the presence of print content. A number of banding defects are added through simulation to a selected set of commercial print contents to form our set of stimuli. The participants in the experiment mark these stimuli based on their observations via a graphical user interface (GUI). Based on the collection of the marked stimuli, our research demonstrates general consistency among different participants. Moreover, the results show that the likelihood of an observer perceiving the banding defect in a smooth area is much higher than in a high frequency area. Furthermore, our results indicate that the luminance of the image may locally affect the visibility of the print defects to a certain degree. In the end of this chapter, we introduce a data analysis method that, for each stimulus, a banding severity level map is generated, which summarizes the banding severity evaluation across all subjects. To improve printer user’s experience and lower customer service cost, web-based print quality troubleshooting (PQTS) tools are developed and introduced in Chapter 2. With detailed instructions in the tool, printer user would be able to diagnostic print quality issues. The easy-to-understand information of most likely causes and troubleshooting suggestions are provided, with pictured step-by-step procedures. Statistics show that our PQTS tools would generate thousands of hits per month. Laser electrophotographic printers are complex systems with many rotating components that are used to advance the media and facilitate the charging, exposure, development, transfer, fusing and cleaning steps. Irregularities that are constant along the axial direction of a roller or drum, which are localized in circumference, can give rise to distinct isolated bands in the output print that are constant in the scan direction. In some occasions, this may be observed to repeat at an interval in the process direction that corresponds to the circumference of the roller or drum responsible for the artifact. In Chapter 3, an image processing and analysis pipeline is designed, which can effectively identify the presence of isolated periodic and aperiodic bands in the output from laser electrophotographic printers. The algorithms that comprise the image processing and analysis pipeline are discussed in detail, and the efficacy and robustness of the pipeline are illustrated with example results. Then, this chapter is concluded with elaboration on the design of a viewing tool which makes it easier for researchers to understand the results. Since the data are corrupted by the presence of aperiodic bands, missing periodic bands and noise, it is necessary to improve the accuracy and robustness for estimating the repetitive interval. A new algorithm based on cost function is designed and discussed in Chapter 4. The effectiveness of this method is illustrated with example results. Lastly, in Chapter 5, a probabilistic model-based method for estimating the repetitive interval is designed and discussed to conclude this research topic. In this chapter, a probabilistic model is designed in detail, and the estimation is examined using simulated data to prove the accuracy and robustness.
Allebach, Purdue University.
Computer Engineering|Electrical engineering
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