manuals in pdf (resolution, compression)

Tom> On Saturday, June 26, 2004, Al Kossow, wrote: Tom> I was doing 150dpi greyscale jpegs. I've changed to 400dpi 1bpp Tom> tiffs, and now I'm ending up with each page about 700K... (scan Tom> as greyscale tiff (unknown compression), convert to 1-bit with Tom> lzw compression, save as pdf in Photoshop). Tom> Using tiffcp to change the compression from lzw to g4 more than Tom> doubles the size to 1.6 MB. That's for a single page. Tom> Surely this is too large? Quite possibly the scan is "dirty". Ideally you'd want the letters to be black and the rest of the page white. More typically, the scan process will put a scattering of black pixels elsewhere on the page, for example due to "bleed through" from the text on the reverse side. If the pages are pretty consistent in quality and color, you can tweak the scan settings to help this, or you can achieve the same result by post-processing in Photoshop or a similar tool. If it has "automation" features (as Photoshop does) you can process lots of pages quickly. The trick is to look for a threshold setting for the black vs. white threshold that results in minimal pixels on the page, but not so high that the letters lose their shape. This is a compromise -- the edge of a printed letter is not really sharp in a scan, so as you raise the threshold some of the outer pixels change from black to white -- your letter gets "thinner". If you can't get both a clean page and an acceptable letter shape, then the source material isn't good enough to support bitonal scanning. If so, you'll need a grayscale scan and you'll have to put up with the larger file sizes that result. paul