- From: David Woolley <david@djwhome.demon.co.uk>
- Date: Thu, 20 Dec 2001 22:54:08 +0000 (GMT)
- To: w3c-wai-ig@w3.org
> maybe I'm wrong but isn't pdf a "photograph" of the page rather than > actual letter codeing, sort of like a fax vs teletype machine?? You are wrong. PDF is essentially PostScript without the programmability (not that many people realise that PostScript is a programming language, these days - it integrates near pixel perfection and a scripting language long before (presentational pseudo-) HTML and JavaScript!). It does have additional navigations features, which have been enhanced for the accessibility features. (Instead of having graphics primitives with variable parameters, and control flow and assignments, PDF is the result of running all the scripting and outputting just the primitives with the final computed numeric and string parameters.) It's somewhat similar to static SVG, except that static SVG doesn't, I believe, support multi-page documents in a single file, and requires separate files for significant bitmaps. PDF is capable of coding text in a way that is easy to recover, but is usually used to postprocess Word documents these days. Word plus the Windows PostScript drivers does extensive microspacing, resulting both in bloat of the PDF file and words being broken up and word spaces not being physically present. That is a fault of the original, generally non-Adobe authoring tools; I expect exactly the same fault in SVG documents produced with the same tools. PDF can be used with legacy documents to take a scanned image and make it look, at first *sight*, as though it is the same as a document prepared from the machine readable source. In my experience, some design consultancies don't understand PostScript and PDF and output bitmaps of brochures and then code them to PDF, but that's a wetware problem. For real scanned images, I believe that Adobe sell a tool that will underlay the scanned image with an OCRed version of the text, so that you can cut and paste the text (and presumably screen read) but still have the accurate rendition of the legacy documentation, visually. > LYNX or at least my version of it chokes on pdf That's because you don't have Acrobat reader or ghostscript in your mailcap file. That those tools may not be good for the blind is a different issue. Note that, by default, PDF is compressed, which is why a plain text viewer will see gibberish, but PDF is actually, like SVG, a basically textual format, and one can have valid PDF documents that are purely textual. This is a fragment of PDF, prepared with groff, which doesn't go overboard with microspacing, although some kerning does break the flow, and with an early version of ghostscript, which doesn't compress (later versions can be forced not to compress). The actual text is in the parentheses. The kerned words are "facings" and "garages". -300.456 -36 Td(1. Summary)Tj /R8 10 Tf 1.318 Tw 25 -15.6 Td(Replace or repair as necessary unsound materials in the f)Tj 1.317 Tw 239.201 0 Td(acings to the g)Tj 3.817 Tw 61.9509 0 Td(arages. Replace)Tj 1.317 Tw 70.3839 0 Td(or repair)Tj
Received on Thursday, 20 December 2001 17:55:11 UTC