Hello, For any list members that are interested in making high-quality scans of halftone material from books and publications, I will now report on a free utility that may be of great use.
High resolution scans (600 dpi) of material that was originally printed with the halftone process will generally preserve the annoying and distracting halftone pattern. Some scanners may offer a "descreening" option to ameliorate this pattern, but most do not. The SANE software also has no descreening provisions. One alternative would be to load a scanned image into the GIMP and then employ the fourier plug-in to remove the low frequency spatial components. Although this method can give excellent results, its use is cumbersome and very time consuming as each image must be processed manually. What is needed is an automatic approach. After some Internet searching, I did discover an automatic tool that will effectively eliminate the halftone pattern from high resolution scans. The source code, which is free and without restrictions, is available here: http://www.picturel.com/halftone/ In conjunction with the SANE package, this utility can produce very fine results. However, there are a few limitations. The code is relatively old (ca. 1998), and can handle only 8-bit images. Also, the utility is meant for grayscale images only. (Because of the nature of color halftoning, decomposing an image into its red, green, and blue channels, followed by descreening and recombining, will give poor results.) However, if these limitations are not that important to you, then by all means you should give this utility a try. The code compiles on 32-bit Linux. (It will compile on x86_64 but will not execute successfully. It apparently is not 64-bit clean.) Perhaps the SANE developers would like to give this code an evaluation for possible inclusion into SANE. Regards, Frank Peters Detroit, Michigan USA
