Classicmag.net

On Fri, Aug 11, 2000 at 05:37:50PM -0400, Jim Oaks wrote: Have you found a good technique for scanning them? It's labor-intensive flipping the pages by hand. Also, the ongoing problem I've had with half-tone images is that the dots beat with the sample dots of the scanner and create a moire pattern. In 1994 I worked with an high-end Arcus scanner which could corrrect this beautifully; most likely it was done in software. But every time I ask supposedly knowledgeable people how to do this in software I get lame answers like "just scan at a higher resolution" or "scan at the same resolution as the dot pitch of the screen" or "use Gaussian blur to smooth the dots together". The first preserves the screen very well, but that is not the goal; the goal is to recreate the original unscreened photo as accurately as possible. The second does not take into account the fact that scanners do not adjust their optical resolution on demand.... a fundamentally 300DPI CCD told to scan at 133 DPI is still going to beat with the halftone dots. The third throws away a lot of information. I suspect the right solution involves a really high-resolution scan, so that each halftone dot is an image in itself; and then use some software technique. The maximum recoverable resolution is probably the same as the dot pitch... or maybe a bit more with the use of edge detection or something like that. I doubt Acrobat solves this problem, but alas, it's not free software, and it runs only on Macs and Windows machines, and costs significant cash so I've never gotten around to trying it out... no doubt I would be disappointed anyway. The Arcus scanner driver required you to specify the screen pitch. I think most likely any software which does not ask you for this information, is not going to do a very good job on screened images. Anyway... the ideal scanner would be able to accept a stack of unbound magazine pages, hundreds at a time, and churn through them without misfeeding; and there would be image processing software to get rid of the moire patterns and make smooth photos of any areas which are screened, always detecting those areas correctly (as opposed to text areas); while also doing Acrobat's tricks of trying to OCR the text, and substituting bitmap areas when that's not possible. I haven't started this project myself because I can't find a method that doesn't suck. Oh... and even if you had all this, some magazines have "sidebars" which are text printed on top of a screened color background; and those usually get detected as images by OCR software, so the text ends up not being searchable. I have tried this using Omnipage, and its image/text differentiation is usually wrong several times per page. Meanwhile, there is a little known image format called DejaVu which I have successfully used; it doesn't try to do any OCR, but it does manage to store a surprisingly good image in a small amount of space. The license terms for it are also not perfect but at least there is a Linux version. You need a free browser plugin to view the images. More info at http://www.djvu.att.com/ For example, check out the Radio Shack DX300 shortwave receiver service manual at http://gw.kb7pwd.ampr.org/manuals/DX300/ Oh and in the end the majority of publishers would probably object to this anyway... especially since they're such big conglomerates, one solid complaint could destroy the biggest share of your work. I'm interested in putting my small collection of Heathkit manuals online too, but those copyrights are owned by a company which sells reprints, and no doubt pursues copyright violations vigorously, since the reprints are their main profit center. Maybe Freenet will enable distribution of this stuff. -- _______ Shawn T. Rutledge / KB7PWD ecloud(a)bigfoot.com (_ | |_) http://www.bigfoot.com/~ecloud kb7pwd(a)kb7pwd.ampr.org __) | | \________________________________________________________________ Get money for spare CPU cycles at http://www.ProcessTree.com/?sponsor=5903