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UBC Theses and Dissertations

Automatic back-up registration for digital thermal halftone proofing Chiu, Peng-Yang Steven

Abstract

Proofing in the printing industry is a vital process of predicting and thus reducing the costs of errors that may show up in the final prints. Digital thermal halftone proofs are produced off-press and offer dot-for-dot match to the press sheet. To produce such proofs with images on both sides of the proof sheets accurately aligned, however, is typically done with skillful manual labor to control and compensate for the thermal expansion of the images due to the step of laminating images to the paper. The alignment of the images is called backup registration. With the introduction of the second generation of thermal proofing media known as direct-to-paper, the lamination step is unnecessary, thus, it is possible to design an automatic backup registration method that can be integrated into many of the existing digital thermal proofing devices. This thesis proposes a novel approach to automatic backup registration by detecting the orientation of the proof sheet (geometric detection), and then adjusting the images on both sides (geometric correction). The geometric detection uses the surface reflectivity differences between the proof sheet and its background to determine the edge positions of the sheet. The geometric correction shifts and rotates the images according to the detected edge positions and various other factors. The proposed algorithm is developed and implemented on Creo Products Inc.'s Spectrum proofing device and numerous two-sided proof samples have been produced to evaluate the precision of backup registration. Since all the samples have demonstrated backup registration within the required 1mm precision and the algorithm is implemented without additional hardware, there is a high possibility of commercial application for the proposed method.

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