Digital press characterization and artifacts prediction and reduction
Abstract
In this dissertation we look at two problems in variable data printing: press characterization and artifacts reduction. Variable data printing (VDP) has become a new solution available for many markets and applications. However, press characterization and artifacts reduction in this new environment bring many challenges. Skew effect can significantly affects the accuracy of the characterization and moire artifacts is a very visually disturbing pattern on printed document. We propose an analytical model of the skew effect in digital press characterization. Digital press characterization gives critical information based on which one can predict how a certain layout, images, and text will be rendered by the press on a particular substrate. Modulation Transfer Function (MTF) analysis characterizes the digital press of interest using MTF test patches designed with different spatial frequencies, tone levels, angles, and colors. These patches are printed and then scanned. However, at high spatial frequencies, a small mis-registration in the scanned image can produce large distortion. Skew is a common image mis-registration introduced in image analysis processes due to the imperfect alignment between the scan target media and the scanning device. The conventional method of de-skewing by rotating the scanned image is not desirable because of the large amount of data in high resolution scans. We present a strategy for rejecting skewed images based on the skew angle and the error tolerance so that they can be rescanned and also a simple procedure to correct the skew effect based on our analytical model. With the introduction of digital press in recent years, the cost of short-run printing jobs has decreased. Traditional proofing methods in print shops focus on human visual inspection of one hardcopy among thousands of print out. However, in variable data printing (VDP), each instance of the same template could use different texts, fonts, and images obtained through various capturing devices. Visual inspection of every copy is not cost efficient. In this dissertation, we first analysis the relationship between the halftone image spectrum and the halftone screen design and then present a scheme to automatically predict the presence of artifacts in the print-out before the actual printing take place. Only the images that may induce artifacts with respect to the targeted press will be identified and adaptive image processing can be applied to eliminate the potential artifacts.
Degree
Ph.D.
Advisors
Allebach, Purdue University.
Subject Area
Electrical engineering
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