Descreening of Halftoning

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Dr. Elisa Barney-Smith


Halftoning is the process a printer uses to print color images using black in combination with three different colored inks: cyan, magenta, and yellow. The printer places dots on the paper at different angles, sizes and frequencies that when combined produce the range of colors that the human visual system can perceive. When a halftone image is scanned and reprinted, the image shows significant degradation due to halftoning artifacts. This can be resolved by filtering the entire image in one step, but the hardware in a printer can only handle 128 x 128 blocks of data. Therefore, the scanned image has to be windowed into small blocks, filtered individually in the frequency domain using a band reject filter, and then recombined before printing. Another problem arises because blocking artifacts are introduced to the image after the filtered windows are recombined. The purpose of this project is to create a model that descreens the scanned image of the halftoning artifacts and removes the blocking artifacts while maintaining the original image quality.

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