De-Screening Low Resolution Halftone Printed Portrait Images

In this paper, one effective descreening method has been proposed for reconstructing continuous tone images from the low screen resolution half-toned (HT) printed document images. This descreening method is much more useful for portraits, engraved, and old historic HT images where screen resolution and dot-shape are important issues. Restructured image quality for descreening or inverse half-tone technique (IHT) greatly depends on these parameters. Conventional IHT generally use high-resolution dispersed-dot HT images, but screen, tonal frequency, shape of halftone dots, and also removal of noise are not seen in broad observation. If even limited halftone patches are present in the HT image or a limited number of HT images are available, then these processes become very difficult or impossible to achieve a good accurate outcome. In this study, we have introduced an improved descreening method or IHT, considering those facts and applied it to various low-resolution half-tone printed images that are usually seen from offset, screen, or lithographic printing. Using two sequential processes, our proposed method converts a low line-tone screen to a continuous tone. A one-inverse half-toning algorithm has been proposed for the first stage, and bilateral filtering and low-pass filtering techniques are used for morphological image decomposition in the second stage to focus on extra smoothing and noise removal. Finally, the reconstructed images have been compared with the original images in terms of standard image quality metrics such as PSNR and SSIM. This study also points to the comparative analysis of IHT for different low-level screen resolution HT images. Our proposed method achieved 0.84 SSIM on 50 lpi HT portrait images.